Producing alpha-olefins using polyketide synthases

This application is a continuation of U.S. application Ser. No. 13/876,727 filed Jun. 24, 2013, which is a national phase of PCT/US2011/053787 filed Sep. 28, 2011, which claims priority to U.S. provisional Application No. 61/387,435 filed Sep. 28, 2010, all of which are incorporated herein by reference in their entirety.

This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy and Award No. 0540879 awarded by the National Science Foundation. The government has certain rights in the invention

The Sequence Listing written in file SEQTXT_77429-011110US-0958337.TXT, created on Sep. 14, 2015, 237,019 bytes, machine format IBM-PC, MS-Windows operating system, is hereby incorporated by reference.

This invention relates generally to α-olefin production using polyketide synthases and so relates to the fields of chemistry, microbiology, and molecular biology.

Type I polyketide synthases (PKSs) are programmable, multifunctional enzymes capable of possessing all of the catalytic capacity of fatty-acid synthases (FASs). However, unlike the FAS enzyme, which iteratively extends and fully reduces the β-carbonyl generated with each extension of the hydrocarbon backbone, PKS systems utilize discrete sets of enzymatic domains for each extension and reduction of the nascent chain. These sets, commonly referred to as modules, can incorporate a variety of extenders units resulting in different side chains. They also can encode between zero and three of the reducing domains associated with FASs, respectively leading to a ketone, hydroxy, double bond, or fully saturated carbon at the beta position of the growing polyketide chain (Hopwood and Sherman. 1990. Annual Review of Genetics 24:37-66).

Due to their modularity, PKS systems have been extensively explored for production of “unnatural” natural products (Weissman and Leadlay. 2005. Nature Reviews Microbiology 3:925-936). Hundreds of these molecules have been produced, ranging from basic lactones to modified versions of drugs and drug-like compounds.

The present invention provides polyketide synthases (PKSs) capable of synthesizing α-olefins, recombinant expression vectors for producing them, recombinant host cells that express them and produce the desired alpha olefin, methods for making alpha olefins, and alpha olefins produced by the methods. The PKSs of the invention are not naturally occurring and so are referred to as “recombinant” PKS enzymes. In some embodiments of the invention, the α-olefin is not a compound synthesized by a naturally occurring PKS. In some embodiments of the invention, the PKS is a hybrid PKS comprising modules and/or portions thereof, from two, three, four or more naturally occurring PKSs. A hybrid PKS can contain naturally occurring modules from two or more naturally occurring PKSs and/or it can contain one or more modules composed of portions, including intact domains, of two or more modules from the same naturally occurring PKS or from two or more naturally occurring PKS, or both. In some embodiments of the invention, a recombinant nucleic acid comprising a CurM module or portion thereof, which may be either naturally occurring or recombinant, is employed.

The present invention provides recombinant nucleic acids that encode PKSs of the invention. The recombinant nucleic acids include nucleic acids that include a portion or all of a PKS of the invention, nucleic acids that further include regulatory sequences, such as promoter and translation initiation and termination sequences, and can further include sequences that facilitate stable maintenance in a host cell, i.e., sequences that provide the function of an origin of replication or facilitate integration into host cell chromosomal or other DNA by homologous recombination. In some embodiments, the recombinant nucleic acid is stably integrated into a chromosome of a host cell. In some embodiments, the recombinant nucleic acid is a plasmid. Thus, the present invention also provides vectors, including expression vectors, comprising a recombinant nucleic acid of the present invention. The present invention also provides host cells comprising any of the recombinant nucleic acid and/or PKS of the present invention. In some embodiments, the host cell, when cultured under suitable conditions, is capable of producing the α-olefin. These host cells include, for example and without limitation, prokaryotes such as E. coli species, Bacillus species, Streptomyces species, Myxobacterial species, as well as eukaryotes including but not limited to yeast and fungal strains.

Thus, the present invention provides a wide variety of host cell comprising one or more of the recombinant nucleic acids and/or PKSs of the present invention. In some embodiments, the host cell, when cultured, is capable of producing an α-olefin that it otherwise does not produce, or produces at a lower level, in the absence of a nucleic acid of the invention.

The present invention provides methods for producing α-olefins, said methods generally comprising: providing a host cell of the present invention, and culturing said host cell in a suitable culture medium under suitable conditions such that the α-olefin is produced.

The present invention also provides compositions comprising an α-olefin from a host cell in which the α-olefin was produced, and in some embodiments may include trace residues and/or other components of the host cell. Such trace residues and/or other components may include, for example, cellular material produced by the lysis of the host cell. The present invention also provides methods of purifying α-olefins and methods for converting them to other useful products.

The foregoing aspects and embodiments of the invention as well as others will be readily appreciated by the skilled artisan from the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings.

FIG. 1 shows an illustrative example of the modular organization of a biosynthetic pathway suitable for synthesizing 1-hexene in accordance with the invention. In this illustration, the proposed modules are sourced from the loading module of DEBS1 from the erythromycin PKS, module 5 from the nystatin PKS NysC, and CurM the terminal module of the curacin PKS. In another embodiment of the invention, the nystatin PKS module 5 is replaced with portions of modules 9 and 10 from the indanomycin PKS; this alternative embodiment has actually been used to produce 1-hexene.

FIG. 2 shows types of modules employed and corresponding precursors utilized for incorporation into polyketide chains. The loading module is designated S. While any suitable loading domain can be used (such as those loading acetate and benzoic acid), only two examples are illustrated in this figure. The remaining compounds represent the structures incorporated into the growing polyketide chain employing extender modules A-P. The dashed line indicates the C—C bond formed through Claisen condensation; atoms to the right of the bond and the C atom at the left of the dashed line represent the structures determined by the module employed. The R group represents the existing acyl chain prior to incorporation determined by the module.

FIGS. 3A-C show: ( FIG. 3A ) a PKS system that can be used to produce 1-hexene in accordance with the invention, ( FIG. 3B ) how additional modules can be added to yield longer, even-chain α-olefins, and ( FIG. 3C ) how changing the loading module to incorporate acetate (from malonyl-CoA) will allow access to the saturated, linear, odd-chain α-olefins in accordance with the methods of the invention.

FIG. 4A shows an embodiment of the invention that illustrates utilization of the avermectin PKS loading module. The side chains illustrated ( FIG. 4B ) are merely examples and do not constitute the entire pool of side chains that can be incorporated using the avermectin loading module (or similar loading modules) in accordance with the methods and teaching of the invention.

FIGS. 5A-B show, in part ( FIG. 5A ), an example of an illustrative pathway to 3-methylenepent-4-enoic acid, an example of the carboxylated butadiene derivatives accessible using PKSs in accordance with the methods of the invention and how the distance between the diene and carboxylate moieties can be increased via the use of additional PKS modules. FIG. 5B shows the proposed mechanism of the exomethylene biosynthesis from the jamaicamide pathway (see Edwards et al. 2004. Chem Biol. 11(6):817-33; incorporated herein by reference).

FIG. 6 shows a PKS for producing butadiene in accordance with the methods of the invention. While this invention is not to be limited in any manner by any proposed mechanism of action recited or shown herein, this figure, for simplicity, illustrates loss of the hydroxyl group as a water molecule, the enzymatic mechanism utilizes sulfate as a leaving group.

FIGS. 7A-G show a PKS for producing butadiene in accordance with the methods of the invention. FIG. 7A and FIG. 7B show the loading of the acrylyl-CoA using the DEBS propionyl-CoA specific loading domain modified to accept acrylyl-CoA. FIG. 7C shows the thiotransfer of the acrylate moiety to KS domain. FIG. 7D shows the binding of the malonyl-CoA and transfer to ACP domain. FIG. 7E shows KS catalyzing the condensation of the moiety with release of CO 2 . FIG. 7F shows KR catalyzing the reduction of the β-carbonyl group. FIG. 7G shows the final step and the release of the butadiene, CO 2 , and water (as in FIG. 6 , the loss of the hydroxyl group is illustrated with a water molecule, but the enzymatic mechanism utilizes sulfate as a leaving group).

FIG. 8 shows an enzymatic pathway accessible by the methods and materials of the invention to produce acrylyl-CoA comprising exogenously supplying propionate, and expressing PrpE and acyl-CoA dehydrogenase activities. A host cell comprising this system would be provided with propionate, which could be exogenously fed to, if not produced endogenously by, the host cell selected for production.

FIG. 9 shows an enzymatic pathway accessible by the methods and materials of the invention to produce acrylyl-CoA comprising exogenously supplying propionate and glucose. A host cell comprising this system would be provided with propionate, either through exogenous feeding or the introduction of propionate biosynthesis pathway, as above, and a suitable organic molecule that the host cell can directly or indirectly convert into a pyruvate. For example, if the host cell is E. coli , the suitable organic molecule can be glucose. This pathway utilizes the central metabolic intermediate pyruvate to produce lactate via a lactate dehydrogenase. Lactate is then converted to lacoyl-CoA by a lactate CoA trnasferase, utilizing propionyl-CoA as a cofactor and releasing propionate. Lactoyl-CoA is then dehydrated using a lactoyl-CoA dehydratase to yield acrylyl-CoA. One embodiment of this invention includes the lactate dehydrogenase, LdhA, from E. coli , the lactate CoA transferase, Pct, from Clostridium proponicum , and the lactoyl-CoA dehydratase enzymes, EI and EII, from C. proponicum . The introduction of this pathway into E. coli or yeast for diene (such as butadiene) production represents a novel application of these enzymes. An embodiment of this invention is use of this pathway for PKS-based acrylate production.

FIG. 10 shows an enzymatic pathway accessible by the methods and materials of the invention to produce acrylyl-CoA starting from the common metabolic precursor malonyl-CoA. This pathway generates malonyl-CoA using an acetyl-CoA carboxylase, acetyl-CoA and CO 2 . Malonyl-CoA is then reduced by a malonyl-CoA reductase releasing malonyl semialdehyde. Malony semialdehyde is converted to 3-hydroxypropionate using a substrate specific oxidoreductase. A 3-hydroxypropionate CoA ligase catalyzes the formation of 3-hydroxypropionyl-CoA. This intermediate is then dehydrated to acryalyl-CoA by the reverse reaction of 3-hydroxypropionyl-CoA hydratase. In one embodiment of the invention, these enzymes are the acetyl-CoA carboxylase complex (AccA/AccD) from E. coli , the malonyl-CoA reductase (The introduction of this pathway into E. coli or yeast for diene (e.g. butadiene) production represents a novel application of these enzymes and is a unique embodiment of this invention. An embodiment of this invention is use of this pathway for PKS-based acrylate production.

FIG. 11 shows an enzymatic pathway accessible by the methods and materials of the invention to produce isoprene via the mevalonate pathway.

FIGS. 12A-F show an example of an illustrative pathway accessible by a PKS provided by the invention for producing isoprene. FIG. 12A shows the loading of the acrylyl-CoA using the DEBS propionyl-CoA specific loading domain modified to accept acrylyl-CoA, and extension with malonyl-CoA to form the beta-keto ACP bound intermediate. FIG. 12B through FIG. 12F show the HMG-CoA-like mechanism involved in the replacement of the β-carbonyl group with a methyl group using PKS enzymes from the PKSX (Bacillaene) cluster from Bacillus subtilis (Butcher, et al. 2007. Proc Natl Acad Sci USA. 104(5):1506-9; incorporated herein by reference). This invention is not to be limited by any proposed mechanism shown herein. In this embodiment, the penultimate product is released as the free acid and subsequently decarboxylated to isoprene in accordance with the methods of the invention by either a decarboxylase, or extracellular chemical catalysis/pyrolysis.

FIG. 13 shows a PKS provided by the invention for producing (E)-penta-1,3-diene. This figure illustrates loss of the hydroxyl group as a water molecule, but the enzymatic mechanism utilizes sulfate as a leaving group.

FIG. 14 shows precursor supply pathways in E. coli for producing acrylyl-CoA, as described in previous figures, and [2S]-methylmalonyl-CoA. Each enzymes depicted can be expressed in a host cell wherein each enzyme can be independently either endogenous or native to the host cell, or introduced into recombinant

FIG. 15 shows methods and materials provided by the invention for maximizing precursor supply pathways in E. coli . The means to maximizing acrylyl-CoA can comprise one or more of “knocking out” (eliminating or reducing the expression of) PrpC activity, knocking out YgfH activity, exogenously feeding propionate (or producing propionate endogenously), overexpressing PrpE activity to increase cytosolic pools of propionyl-CoA. From this intermediate, the introduction of the propionyl-CoA carboxylase complex (AccA/PccB) will yield methylmalonyl-CoA (Pfeifer, et al. Science. 2001 Mar. 2; 291(5509):1790-2; incorporated herein by reference). This pool of propionyl-CoA can also be utilized in the pathways described in FIGS. 8 and 9 .

FIG. 16 shows an illustrative PKS provided by the invention to produce 3-hydroxy-1-octene. The PKS comprises the following elements: (i) Load module and KS1 from PikA1 (pikromycin), followed by (ii) Module 1 and KS2: AT-ACP segment from Module 5 and KS6 domain from the Nystatin PKS, (iii) Module 2: the hydroxymalonate-specifc AT and contiguous ACP domains from ZmaA (zwittermicin PKS) from Bacillus cereus , DH, ER and KR domains from nanchangmycin PKS Module 2, and (iv) Module 3: AT-TE segment of the CurM module (curacin PKS). For the production of the precursor hydroxymalonyl-ACP, enzymes ZmaD, ZmaG, and ZmaE are also produced by or provided to the host strain. This figure illustrates loss of the hydroxyl group as a water molecule, however, it should be noted that the enzymatic mechanism utilizes sulfate as a leaving group.

FIG. 17 shows an illustrative PKS provided by the invention to produce 1-decene. The PKS comprises the following elements: (i) Load module and KS1 from PikA1, followed by (ii) Module 1 and KS2: AT-ACP segment from Module 5 and KS6 domain from the nystatin PKS, (iii) Module 2 and KS3: AT-ACP segment from Module 15 and KS16 domain from the nystatin PKS, (iv) Module 3 and KS4: AT-ACP segment from Module 3 and K4 domain from the oligomycin PKS, and (v) Module 4: AT-TE segment from CurM. This figure illustrates loss of the hydroxyl group as a water molecule, however, it should be noted that the enzymatic mechanism utilizes sulfate as a leaving group.

FIG. 18 shows an illustrative PKS provided by the invention to produce 1-octene. The PKS comprises the following elements: (i) Loading Module and KS1 from PikA1, followed by (ii) Module 1 and KS2: AT-ACP segment from Module 5 and KS6 domain from the nystatin PKS Module 2, (iii) and KS3: AT-ACP segment from Module 15 and KS16 domain from the nystatin PKS, and then (iv) Module 3: AT-ST segment from the CurM module. This figure illustrates loss of the hydroxyl group as a water molecule, however, it should be noted that the enzymatic mechanism utilizes sulfate as a leaving group.

This invention is not limited to particular embodiments described, as such may, of course, vary. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, because the scope of the present invention will be limited only by the appended claims.

Where a range of values is provided, each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention.

Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in practicing the present invention, suitable methods and materials are now described. All publications cited are incorporated herein by reference to disclose and describe the methods and/or materials and/or results therein.

As used herein and in the appended claims, the singular forms “a”, “and”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an α-olefin” includes a plurality of such α-olefins, and so forth.

The term “even-chain α-olefin” refers to an α-olefin with a carbon backbone, which, disregarding any functional groups or substituents, has an even number of carbon atoms.

The term “odd-chain α-olefin” refers to an α-olefin with a carbon backbone, which, disregarding any functional groups or substituents, has an odd number of carbon atoms.

The term “functional variant” describes an enzyme that has a polypeptide sequence that is at least 70%, 75%, 80%, 85%, 90%, 95% or 99% identical to an enzyme described herein. A “functional variant” enzyme may retain amino acids residues recognized as conserved for the enzyme in nature, and/or may have non-conserved amino acid residues. Amino acids can be, relative to the native enzyme, substituted (different), inserted, or deleted, but the variant has generally similar enzymatic activity as compared to an enzyme described herein. A “functional variant” enzyme may be found in nature or be an engineered mutant (recombinant) thereof.

The objects, advantages, and features of the invention will become more apparent to those persons skilled in the art upon reading the details of the invention as more fully described below.

Polyketide Synthases (PKS)

The present invention provides recombinant polyketide synthase (PKS) enzymes capable of synthesizing an α-olefin. The PKS enzymes of the invention are not naturally occurring PKS. In some embodiments of the invention, the α-olefin is not a compound synthesized by a naturally occurring PKS. In some embodiments of the invention, the PKS is a hybrid PKS comprising modules, domains, and/or portions thereof, or functional variants thereof, from two or more PKSs. Such α-olefins include the diketides and triketides, and polyketides of more than three ketide units, such as 4, 5, or 6 or more ketide units. The α-olefin can further include one or more functional groups in additional to the double bond that characterizes them. Such functional groups include, but are not limited to, ethyl, methyl and hydroxy side chains, internal olefins, and ketones.

In some embodiments of the invention, the α-olefin is an even-chain α-olefin having the following chemical structure:

wherein each R 1 is independently —H or —CH 3 , each R 2 is independently —H or —OH, n is an integer, and αβ is a single or double bond, with the proviso that when an αβ is a double bond then the corresponding R 2 is H. In some embodiments of the invention, n is an integer from 1 to 10. n indicates the number of two-carbon-chain subunits in the carbon backbone of the α-olefin. The R 1 , R 2 , and αβ within each two-carbon-subunit of a multiple subunit α-olefin is independent of the R 1 , R 2 , and αβ of any other two-carbon-subunit in the molecule. In some embodiments, however, one or more, up to all, subunits have identical R 1 , R 2 , and αβ.

In some embodiments of the invention, the α-olefin has the following chemical structure:

wherein n is an integer from 0 to 10.

In one embodiment, the invention provides methods, host cells, and nucleic acids for making the C3-alpha olefins propylene (propene) and polymers and products derived therefrom, including but not limited to: polypropylene, acylonitrile, propylene oxide, alcohols, cumene, acrylic acid, injection molded plastics, electronics, electrical appliances, housewares, bottle caps, toys, luggage, films, fibers, carpets, clothing, ropes, pipes, conduit, wire, cable, elastomeric polymers, acrylic fibers, nitrile rubber, acrylonitrile-butadiene-styrene (ABS) resins, styrene-acrylonitrile (SAN) resins, acrylamide, adiponitrile, polyether polyols, polyurethanes, flexible foams, rigid foams, insulation, propylene glycol, polyester resins, antifreeze, de-icing fluids, propylene glycol ethers, paints, coatings, inks, resins, cleaners, isopropanol, cosmetics, pharmaceuticals, food, ink, adhesives, 2-ethylhexanol, phthalate plasticizers, phenol, acetone, polycarbonate, phenolic resins, epoxy resins, methyl methacrylate (MMA), and acrylic esters.

In one embodiment, the invention provides methods, host cells, and nucleic acids for making the C4-alpha olefin butene and polymers and products derived therefrom, including but not limited to: polybutylene, copolymers with ethylene and/or propene, hot-melt adhesives, synthetic rubber, diesel fuel, and jet fuel.

In one embodiment, the invention provides methods, host cells, and nucleic acids for making the C4 diolefin butadiene and polymers and products derived therefrom, including but not limited to: styrene butadiene rubber (SBR), polybutadiene rubber, acrylonitrile butadiene styrene (ABS), styrene butadiene (SB) copolymer latex, nitrile rubber, adiponitrile, chloroprene, butanediol, tetrahydrofuran, tires, adhesives, coatings, high impact polystyrene, thermoplastic resins, engineering nylons (from C12 lactam), paper coating, gaskets and seals, hoses, gloves, nylon fibers, polymers, wet suits, electrical insulation, polybutylene terephthalate, spandex, and binders. Butadiene has the following chemical structure:

In one embodiment, the invention provides methods, host cells, and nucleic acids for making the C5 α olefin: 1-pentene and polymers and products derived therefrom, including but not limited to: gasoline, polymers, adhesives, sealants, diesel fuel, and jet fuel.

In one embodiment, the invention provides methods, host cells, and nucleic acids for making the C6 α-olefin (see FIG. 1 , example): 1-hexene and polymers and products derived therefrom, including but not limited to comonomer, polyethylene, polymer, high density polyethylene (HDPE), linear low density polyethene (LLDPE), 1-heptanal, heptanoic acid, resin, film, plastic pipe, containers, diesel fuel, and jet fuel. 1-hexene has the following chemical structure:

and an illustration of a 1-hexene producing PKS is provided in FIG. 1 .

In one embodiment, the invention provides methods, host cells, and nucleic acids for making the C10 α-olefin: 1-decene and polymers and products derived therefrom, including but not limited to: detergent formulations, linear alkyl benzene (LAB), linear alkyl benzene sulfonate (LABS), polyalphaolefin synthetic lubricant basestocks (PAO), heatshrink materials, electrical insulation sleeves, rash guards in clothing, polyolefin elastomers (POE), flexible foams, footwear, seat cushions, armrests, pillows, radar coolants, strings, polyol esters, detergent alcohols, plasticizer alcohols, specialty chemicals, epoxides, derivatives thereof, comonomer, intermediate in production of epoxides, amines, oxo alcohols, synthetic lubricants, synthetic fatty acids, alkylated aromatics, emulsifiers, performance waxes, cosmetic formulations, viscosity controller, solvent, decene butene copolymer, binder, film forming, decene/PVP copolymer, food additives, glazing agent, anti-foaming agent, anti-dusting agent, white mineral oil substitute, polishing agent, well fluids, alpha olefin oligomers, and the like. 1-decene has the following chemical structure:

In one embodiment, the invention provides methods, host cells, and nucleic acids for making the C8 aromatic α-olefin: styrene and polymers and products derived therefrom, including but not limited to: homopolymers, copolymers, polystyrene, expandable polystyrene (EPS), acrylonitrile-butadiene-styrene (ABS), resins, styrene-acrylonitrile (SAN), acrylonitrile-styrene-acrylate (ASA), styrene butadiene, styrene butadiene rubber, copolymer with maleic anhydride, terephthalate, unsaturated polyester resins, containers, closures, lids and vending cups, construction; electrical and electronic parts; domestic appliances and housings; household goods and home furnishings; and toys, sporting goods and recreational articles, packaging, thermoplastics, cutlery, CDs, insulating materials, polymer bonded explosives, consumer products, renewable plastics, renewable products, hardhats, tires, etc. In some embodiments of the invention, the aromatic α-olefin has the following chemical structure:

wherein R 3 is —H, —OH, —NH 3 , or —NO 2 .

Alpha olefins are commonly used in the cosmetics and skin care industry, and the present invention therefore provides useful starting materials for making cosmetics and skin care products. For example, alpha olefin sulfonate, sulfate free personal cleaners, soap, copolymer maleic acid, and the like are all used in these industries and provided by the invention. Alpha olefins provide by the invention can also be used in the flavor and fragrance industry. For example, 3-hydroxy-1-octene and 3-oxo-1-octene can be made using the methods and materials of the invention and are used in applications where a mushroom flavor/fragrance is desired.

The present invention can also be used to generate intermediates useful in the synthesis of pharmaceuticals. These olefins can be coupled via olefin metathesis to one another or other olefin intermediates obtained via traditional chemical syntheses to yield bioactive molecules useful as drugs.

In some embodiments, the α-olefin produced in accordance with the invention is (E)-deca-1,5-diene, which has the following chemical structure:

In some embodiments, the α-olefin produced in accordance with the invention has the following chemical structure:

wherein R is one of the following structures:

In some embodiments, the α-olefin produced in accordance with the invention is a polyolefin having chemical structure (I) and comprising at least two, three, four, five, or more C—C double bonds. Such α-olefins include, but are not limited to, diolefins, such as diolefins with two C—C double bonds on the carbon backbone. Such diolefins include, but are not limited to, butadiene, isoprene, and penta-1,3-diene. Butadiene has the chemical structure shown in [0043], above.

In some embodiments, the α-olefin produced in accordance with the invention is isoprene, which has the following chemical structure:

In some embodiments, the α-olefin produced in accordance with the invention is penta-1,3-diene, which has the following chemical structure:

Complex polyketides comprise a large class of natural products that are synthesized in bacteria (mainly members of the actinomycete family; e.g. Streptomyces ), fungi and plants. Polyketides form the macrolactone component of a large number of clinically important drugs, such as antibiotics (e.g. erythromycin, tylosin), antifungal agents (e.g. nystatin), anticancer agents (e.g. epothilone), immunosuppressives (e.g. rapamycin), etc. Though these compounds do not resemble each other either in their structure or their mode of action, they share a common basis for their biosynthesis, which is carried out by a group of enzymes designated polyketide synthases.

Polyketide synthases (PKS) employ short chain fatty acyl CoAs in Claisen condensation reactions to produce polyketides. Unlike fatty acid synthases that utilize acetyl CoA as the starter and malonyl CoA as the extender units, and use a single module iteratively to produce the nascent acyl chains, PKSs are composed of discrete modules, each catalyzing the chain growth of a single step. Modules can differ from each other in composition, so that, overall, a number of different starters (e.g. acetyl CoA, propionyl CoA) and extenders, some of which contain stereospecific methyl (or ethyl) side chains can be incorporated into a polyketide. In addition, PKS modules do not always reduce the 3-carbonyl formed from condensation but may leave it either unreduced (ketone), partially reduced (hydroxyl, 2,3-ene), or fully reduced (3-methylene). Many PKSs employ malonyl CoA or [S]-2-methylmalonyl CoA as the starter for polyketide synthesis. In such cases, the terminal carboxyl group is usually removed by a decarboxylase domain present at the N-terminus of the loading domain of the PKS. Thus, the structure (and chirality) of the α-carbon and β-carbonyl is determined by the module of the PKS employed in the synthesis of the growing chain at each particular step. Because of the correspondence between the modules used in the synthesis and the structure of the polyketide produced, it is possible to program PKS synthesis to produce a compound of desired structure by selection and genetic manipulation of polyketide synthases.

FIG. 2 shows the various modules and the precursor utilized by each module for incorporation into the corresponding nascent acyl (polyketide) chain to give rise to a range of compounds of interest. Table 1, below, provides illustrative PKS sources for each module in FIG. 2 . Each PKS source (amino acid sequence and corresponding coding sequence) is well-known to one skilled in the art and readily available. In addition, for each module in Table 1, there are other modules from other PKS (or from recombinant DNA technology) that can be used. In addition, other structures can be incorporated in the ketide or polyketide that are not shown in Table 1 and FIG. 2 . For example, useful loading modules includer the benzoate loading module of soraphen PKS, the isobutyrate loading module of the lipomycin PKS and bafilomycin PKS, and the acrylate loading module from the dificidin pathway. The acrylate loading module from the dificidin PKS loads and dehydrates a hydroxypropionate molecule by the use of enzymes difA-E to yield a PKS with an arylyl-ACP (Chen, 2006, J. Bact. 188:4024-4036; incorporated herein by reference).

The present invention also contemplates the use of functional variants of PKS modules, domains, and portions thereof. In one important embodiment, the invention provides a variety of recombinant modules that carry out the same enzymatic reactions conducted by the CurM module.

All extender modules carry the β-acyl ACP synthase (commonly called the ketosynthase or KS) domain, which conducts the decarboxylative condensation step between the extender and the growing polyketide chain, and the acyl carrier protein (ACP) domain that carries the growing acyl chain and presents it to any cognate reductive domains for reduction of the β-carbonyl. Modules can differ from each other in composition so that a number of different starter and extender units, some of which contain stereospecific side chains (e.g. methyl, ethyl, propylene) can be incorporated. The acyltransferase (AT) domain of each module determines the extender unit (e.g. malonyl CoA, methylmalonyl CoA, and the like) incorporated. In addition, PKS modules do not always reduce the β-carbonyl formed from condensation but may leave it either unreduced (ketone), partially reduced (hydroxyl, 2,3-ene) or fully reduced (3-methylene), as shown in FIG. 2 . The ketoreductase (KR) domain reduces the ketone to the OH function (stereospecifically); the dehydratase (DH) domain removes water from the α and β carbons leaving an α,β trans-double bond; the enoylreductase (ER) domain reduces the double bond to a β-methylene center; the reductive state of the β-carbonyl, therefore, is determined by the presence of functional reductive domains in the corresponding module. Less commonly, modules may contain an additional C-methylation domain (yielding an additional α-methyl side chain, as in epothilone).

The Curacin A Chain Termination Module is annotated as CurM. CurM catalyzes an extension of the nascent polyketide molecule with acetate (from malonyl-CoA). The resulting beta carbonyl is reduced to a hydroxyl group by a KR domain. The resulting beta hydroxyl group is then sulfonated by the ST domain (from the common metabolic precursor 3′-phosphoadenosine-5′-phosphosulfate). The TE domain releases the 3-sulfo polyketide which then undergoes loss of sulfate and a decarboxylation to form a terminal olefin moiety. The chain termination module of the PKS of the present invention can comprise the ST and TE domains of the CurM Chain Termination Module and variants thereof with similar activity. Additional PKS modules carrying the combination of a sulfotransferase (pfam00685)/thioesterase have been identified in nature and can be used in additional embodiments of the invention. One such olefination module (Ols) has been characterized from Synechococcus sp. strain PCC 7002 (Mendez-Perez et al. 2011. Appl. Env. Microbiol. 77:4264-4267 2011). Others include, but are not limited to, PKS enzymes from Cyanothece sp. PCC 7424, Cyanothece sp. PCC 7822, Prochloron didemni P1-Palau, Pseudomonas entomophila L48, and Haliangium ochraceum DSM 14365. The present invention also provides consensus sequences that differ from these naturally occurring sequences but encode similar enzymatic activities.

The makeup of the PKS, therefore, determines the choice of starter and extender acyl units incorporated, the extent of reduction at each condensation step, and the total number of units added to the chain. The wide diversity of structures of polyketides seen in nature is thus attributable to the diversity in PKS enzymes.

A partial list of PKS amino acid and corresponding nucleic acid coding sequences that can be used in the PKSs of the present invention includes, for illustration and not limitation, Ambruticin (U.S. Pat. No. 7,332,576); Avermectin (U.S. Pat. No. 5,252,474; MacNeil et al., 1993, Industrial Microorganisms: Basic and Applied Molecular Genetics, Baltz, Hegeman, & Skatrud, eds. (ASM), pp. 245-256; MacNeil et al., 1992, Gene 115: 119-25); Candicidin (FRO008) (Hu et al., 1994, Mol. Microbiol. 14: 163-72); Curacin A (Chang et al., 2004, J. Nat. Prod., 67 (8), pp 1356-1367; Gu et al., 2009, J. Am. Chem. Soc., 131 (44), pp 16033-16035); Epothilone (U.S. Pat. No. 6,303,342); Erythromycin (WO 93/13663; U.S. Pat. No. 5,824,513; Donadio et al., 1991, Science 252:675-79; Cortes et al., 1990, Nature 348:176-8); FK506 (Motamedi et al., 1998, Eur. J. Biochem. 256:528-34; Motamedi et al., 1997, Eur. J. Biochem. 244:74-80); FK520 or ascomycin (U.S. Pat. No. 6,503,737; see also Nielsen et al., 1991, Biochem. 30:5789-96); Jerangolid (U.S. Pat. No. 7,285,405); Leptomycin (U.S. Pat. No. 7,288,396); Lovastatin (U.S. Pat. No. 5,744,350); Nemadectin (MacNeil et al., 1993, supra); Niddamycin (Kakavas et al., 1997, J. Bacteriol. 179:7515-22); Oleandomycin (Swan et al., 1994, Mol. Gen. Genet. 242:358-62; U.S. Pat. No. 6,388,099; Olano et al., 1998, Mol. Gen. Genet. 259:299-308); Pederin (PCT publication no. WO 2003/044186); Pikromycin (Xue et al., 2000, Gene 245:203-211); Pimaricin (PCT publication no. WO 2000/077222); Platenolide (EP Pat. App. 791,656); Rapamycin (Schwecke et al., 1995, Proc. Natl. Acad. Sci. USA 92:7839-43); Aparicio et al., 1996, Gene 169:9-16); Rifamycin (August et al., 1998, Chemistry & Biology, 5: 69-79); Soraphen (U.S. Pat. No. 5,716,849; Schupp et al., 1995, J. Bacteriology 177: 3673-79); Spiramycin (U.S. Pat. No. 5,098,837); and Tylosin (EP 0 791,655; Kuhstoss et al., 1996, Gene 183:231-36; U.S. Pat. No. 5,876,991); each of the foregoing references is incorporated herein by reference. Additional suitable PKS coding are readily available to one skilled in the art (e.g., by cloning and sequencing of DNA from polyketide producing organisms or by reference to GenBank).

Of the more than one hundred PKSs studies and reported on in the scientific literature, the correspondence between the modules used in the biosynthesis of, and the structure of, the polyketide produced is understood both at the level of the protein sequence of the PKS and the DNA sequence of the corresponding genes. The organization of modules and correspondence with polyketide structure can be identified by amino acid and/or nucleic acid sequence determination. One can thus clone (or synthesize) DNA sequences corresponding to desired modules and transfer them as fully functioning units to heterologous hosts, including otherwise non-polyketide producing hosts such as E. coli (Pfeifer, et al., Science 291, 1790 (2001); incorporated herein by reference), and polyketide-producing hosts, such as Streptomyces (Kao et al., Science 265, 509 (1994); incorporated herein by reference).

Additional genes employed in polyketide biosynthesis have also been identified. Genes that determine phosphopantetheine:protein transferase (PPTase) that transfer the 4-phosphopantetheine co-factor of the ACP domains, commonly present in polyketide producing hosts, have been cloned in E. coli and other hosts (Weissman et al., Chembiochem 5, 116 (2004); incorporated herein by reference). While it is possible to re-program polyketide biosynthesis to produce a compound of desired structure by either genetic manipulation of a single PKS or by construction of a hybrid PKS composed of modules from two or more sources (see Weissman et al., supra), the present invention provides the first means for making an alpha-olefin by a recombinant PKS.

Recombinant methods for manipulating modular PKS genes to make the PKSs of the present invention are described in U.S. Pat. Nos. 5,672,491; 5,843,718; 5,830,750; 5,712,146; and 6,303,342; and in PCT publication nos. WO 98/49315 and WO 97/02358; each of which is incorporated herein by reference. A number of genetic engineering strategies have been used with various PKSs to demonstrate that the structures of polyketides can be manipulated to produce novel polyketides (see the patent publications referenced supra and Hutchinson, 1998, Curr. Opin. Microbiol. 1:319-329, and Baltz, 1998, Trends Microbiol. 6:76-83; incorporated herein by reference). In some embodiments, the components of the hybrid PKS are arranged onto polypeptides having interpolypeptide linkers that direct the assembly of the polypeptides into the functional PKS protein, such that it is not required that the PKS have the same arrangement of modules in the polypeptides as observed in natural PKSs. Suitable interpolypeptide linkers to join polypeptides and intrapolypeptide linkers to join modules within a polypeptide are described in PCT publication No. WO 00/47724, incorporated herein by reference.

The vast number of polyketide pathways that have been elucidated to date and the present invention in combination provide a variety of different options to produce α-olefins in accordance with the invention. While the products can be vastly different in size and functionality, all employ similar methods for preparing the PKS and corresponding coding sequence and for producing the desired α-olefin. The interfaces between non-cognate enzyme partners can be optimized on a case-by-case basis. ACP-linker-KS and ACP-linker-TE regions from the proteins of interest will be aligned to examine the least disruptive fusion point for the hybrid synthase. Genetic constructions will employ sequence and ligation independent cloning (SLIC), or other sequence independent cloning techniques, so as to eliminate the incorporation of genetic “scarring”.

In some embodiments, the PKS that produces the α-olefin of interest comprises the sulfotransferase (ST)-thioesterase (TE) domains from Lyngbya majuscula CurM or similar domains from another naturally occurring PKS or one of the recombinant domains provided by the invention. The α-olefins capable of being produced by the invention include, but are not limited to, the diketides propylene, 1-butene, and styrene and the triketides 1-hexene and 1-pentene. In one aspect of the invention, the host cell is fed or exogenously provided or endogenously produces acrylate and so produces diolefins such as 1,5-hexadiene and butadiene. In another aspect, feeding or exogenously providing or endogenous production of benzoic acid to the host cell comprising a PKS of the invention enables the production of styrene derivatives.

In some embodiments, host cells that are capable of producing diolefins are also capable of producing acrylate or acrylyl-CoA/ACP, thus eliminating the need for exogenous acrylate. By coupling one of many PKS thioesterase domains to the module loading acrylate from these precursor pathways, the PKS system is capable of producing acrylic acid. Acrylic acid can also be obtained from acrylyl-CoA or acrylyl-ACP by use of a non-PKS hydrolase in accordance with the invention. In some embodiments of the invention, host cells that are capable of producing diolefins are also capable of producing benzoate.

L. majuscula CurM ST-TE domains comprise the following amino acid sequence:

L. majuscula CurM ST domain comprises the following amino acid sequence:

L. majuscula CurM TE domain comprise the following amino acid sequence:

In some embodiments, the PKS of the present invention comprises a naturally occurring sulfotransferase-thioesterase (ST-TE) domains, or ST or TE domain, functionally similar, but not identical, to L. majuscula CurM. In some embodiments, the PKS of the present invention comprises the amino acid sequences of the ST and/or TE of any of the proteins/peptides described in Tables 2-4, or functionally variants thereof. One skilled in the art can identify such L. majuscula CurM-like ST and/or TE domains using available bioinformatics programs. For example, the L. majuscula CurM ST-TE can be split in two separately functional portions by relying on its crystal structure and annotation of catalytic boundaries with programs like protein BLAST, and the sequences can be homology-modeled to get a better grasp of the boundary of catalytic domains, using L. majuscula CurM ST-TE as an anchoring template. Together, such methods can be employed to make solid predictions about catalytic activity and responsible amino acid regions within a larger protein.

In some embodiments, ST and/or TE domains, or functionally variants thereof, comprise one or more of the following amino acid residues (using L. majuscula CurM as a reference sequence): R205, H266, S100, E124, N211, and N267. In some embodiments, ST and/or TE domains, or functionally variants thereof, comprise the following amino acid residues (using L. majuscula CurM as a reference sequence): R205 and H266, and optionally one or more of S100, E124, N211, and N267. In some embodiments, the PKS comprises a ST domain and a TE domains that are derived or obtained from two different organisms or sources.

In some embodiments of the invention, a precursor molecule, such as propionate or acrylate, is provided to the PKS to produce a polyketide of interest. The precursor molecule can be fed or exogenously provided to or endogenously produced by the host cell comprising the PKS, or the host cell can produce the enzymes capable of biosynthesizing the precursor molecule from a simpler molecule that can be fed or exogenously provided to the host cell or the host cell naturally endogenously produces. For example, Streptomyces species produces propionyl-CoA as part of its innate metabolism, thus eliminating the need for exogenous propionate provision.

In some embodiments of the invention, the PKS capable of producing an α-olefin of interest comprises CurM, the terminal PKS from the curacin biosynthesis pathway (Chang, 2004) or a similar module. CurM is a monomodular PKS protein containing an unusual sulfotransferase domain. This domain sulfonates the beta hydroxyl group of the penultimate product and the combination of the ST-TE domains catalyze a decarboxylation and functional dehydration (with sulfate as the leaving group) to yield the terminal olefin. FIG. 1 illustrates how domains from CurM can be coupled to other PKS enzymes to produce an α-olefin, such as 1-hexene, in accordance with the methods and materials of the invention. In the example shown in FIG. 1 , first PKS ORF encodes a loading module specific for propionate (via the CoA) and an extension module that incorporates acetate (via malonyl-CoA) and fully reduces the β-carbonyl. In this example shown in FIG. 1 , the loading domain is from the erythromycin PKS (Donadio et al. 1991. Science 675-679; incorporated herein by reference) and module 5 is from the nystatin PKS (Brautaset et al. 2000. Chemistry & Biology 7:395-403; incorporated herein by reference), but there are other modules that can be used to provide the same product. The second and third proteins that constitute the multi-subunit PKS in this example come from the curacin PKS and corresponding gene cluster (see Chang et al. 2004. Journal of Natural Products 67:1356-1367; sequence updated in Gu et al. J Am Chem Soc. 2009 Nov. 11; 131(44):16033-5; both of which are incorporated herein by reference). Using this PKS, the first two modules can be replaced with any of several well characterized modules to yield several dozen different α-olefins. Increasing the number of upstream modules to three or more increases the number of different products into the hundreds and higher.

To ensure appropriate interactions between the two PKS proteins in this and related examples, one can use the acyl-carrier protein (ACP) and C-terminus from CurM's native enzyme partner, CurL. In general, native C- and N-terminal docking partners can be used in the combinatorial PKS enzymes of the invention. Other cognate domains from different PKS enzymes can also be used.

FIG. 3A shows an exemplary PKS for producing a triketide α-olefin. FIGS. 3B and 3C show exemplary extensions of this model, demonstrating how additional modules can be employed to yield longer, fully saturated, linear α-olefins.

Incorporation of the avermectin loading domain into a PKS of the invention provides access to a number of other α-olefins. Some examples of this aspect of the invention to make both known and novel α-olefins are shown in FIG. 4 .

In some embodiments, the PKS of the invention produces a butadiene with a pendant acid moiety, such that the butadiene is suitable for subsequent crosslinking FIG. 5 shows such a PKS that comprises a set of enzymes comprising an HMG-like system found in several PKS enzymes and corresponding gene clusters. This system converts the β-carbonyl to a number of different chemical moieties, most pertinently an exomethylene. Briefly, one of the previously described systems for incorporating an acrylate starter (DEBS (Donadio et al. 1991. supra) or difficidin (Chen et al. 2006. J Bacteriol. 188(11):4024-36; incorporated herein by reference) loading module) can be fused to an HMG-like module, such as JamE from the jamaicamide cluster (Edwards et al. 2004. Chem Biol. 11(6):817-33; incorporated herein by reference), and a TE domain at the C-terminus. Such a bimodular PKS enzyme can be co-expressed with the genes encoding accessory proteins required for the incorporation of the desired chemistry. In this example these enzymes are JamH, JamG and JamI (Edwards et al., 2004, supra).

In some embodiments of the invention, the PKS comprises a CurM chain termination module of Lyngbya majuscula CurM or functionally equivalent module. In some embodiments of the invention, the PKS comprises the ST and TE domains of the curM chain termination module and sequences derived from a different CurM module or another PKS entirely. In some embodiments of the invention, the PKS comprises the KR, ACP, ST and TE domains of the CurM chain termination module and sequences derived from a different CurM module or another PKS entirely. In some embodiments of the invention, the PKS comprises the AT, KR, ACP, ST and TE domains of the CurM chain termination module and sequences derived from a different CurM module or another PKS entirely.

In some embodiments, the PKS of the invention comprises an acrylate loading module, such as the acrylate loading module from the dificidin PKS (Chen et al., 2006, supra), which incorporates the acrylyl moiety from a hydroxypropionate precursor involving the enzymes difA-E.

The present invention also provides a PKS comprising an acrylate loading module coupled to a thioesterase domain, wherein the PKS is capable of producing acrylate (acrylic acid). The erythromycin PKS, for example and without limitation, includes suitable such modules and domains.

The following depict the amino acid sequences of SEQ ID NO:1-9

L. majuscula CurM (GenBank: ACV42478.1) has the following amino acid sequence (SEQ ID NO:1):

HexORF1 has the following amino acid sequence (SEQ ID NO:2):

HexORF1′ has the following amino acid sequence (SEQ ID NO:3):

HexORF2 has the following amino acid sequence (SEQ ID NO:4):

The amino acid sequence of a PKS capable of producing 1-butene has the following amino acid sequence (SEQ ID NO:5):

The amino acid sequence of a PKS capable of producing propene has the following amino acid sequence (SEQ ID NO:6):

The amino acid sequence of a PKS capable of producing styrene has the following amino acid sequence (SEQ ID NO:7):

The amino acid sequence of a PKS (pentene ORF1) capable of producing pentene has the following amino acid sequence (SEQ ID NO:8):

The amino acid sequence of a PKS (pentene ORF2) capable of producing pentene has the following amino acid sequence (SEQ ID NO:9):

MSNEEKLREYLRRALVDLHQARERLHEAESGEREPIAIVAMGCRYPGGVQ DPEGLWKLVASGGDAIGEFPADRGWHLDELYDPDPDQPGTCYTRHGGFLH DAGEFDAGFFDISPREALAMDPQQRLLLEISWETVESAGMDPRSLRGSRT GVFAGLMYEGYDTGAHRAGEGVEGYLGTGNAGSVASGRVAYAFGFEGPAV TVDTACSSSLVALHLACQSLRQGECDLALAGGVTVMSTPERFVEFSRQRG LAPDGRCKSFAAAADGTGWGEGAGLVLLERLSDARRNGHRVLAVVRGSAV NQDGASNGLTAPNGLAQERVIQQVLTSAGLSASDVDAVEAHGTGTRLGDP IEAQALIAAYGQDRDRDRPLWLGSVKSNIGHTQAAAGVAGVIKMVMAMRH GELPRTLHVDEPNSHVDWSAGAVRLLTENIRWPGTGTRRAGVSSFGVSGT NAHVIVGDYAQQKSPLAPPATQDRPWHLLTLSAKNAQALNALQKSYGDYL AQHPSVDPRDLCLSANTGRSPLKERRFFVFKQVADLQQTLNQDFLAQPRL SSPAKIAFLFTGQGSQYYGMGQQLYQTSPVFRQVLDECDRLWQTYSPEAP ALTDLLYGNHNPDLVHETVYTQPLLFAVEYAIAQLWLSWGVTPDFCMGHS VGEYVAACLAGVFSLADGMKLITARGKLMHALPSNGSMAAVFADKTVIKP YLSEHLTVGAENGSHLVLSGKTPCLEASIHKLQSQGIKTKPLKVSHAFHS PLMAPMLAEFREIAEQITFHPPRIPLISNVTGGQIEAEIAQADYWVKHVS QPVKFVQSIQTLAQAGVNVYLEIGVKPVLLSMGRHCLAEQEAVWLPSLRP HSEPWPEILTSLGKLYEQGLNIDWQTVEAGDRRRKLILPTYPFQRQRYWF NQGSWQTVETESVNPGPDDLNDWLYQVAWTPLDTLPPAPEPSAKLWLILG DRHDHQPIEAQFKNAQRVYLGQSNHFPTNAPWEVSADALDNLFTHVGSQN LAGILYLCPPGEDPEDLDEIQKQTSGFALQLIQTLYQQKIAVPCWFVTHQ SQRVLETDAVTGFAQGGLWGLAQAIALEHPELWGGIIDVDDSLPNFAQIC QQRQVQQLAVRHQKLYGAQLKKQPSLPQKNLQIQPQQTYLVTGGLGAIGR KIAQWLAAAGAEKVILVSRRAPAADQQTLPTNAVVYPCDLADAAQVAKLF QTYPHIKGIFHAAGTLADGLLQQQTWQKFQTVAAAKMKGTWHLHRHSQKL DLDFFVLFSSVAGVLGSPGQGNYAAANRGMAAIAQYRQAQGLPALAIHWG PWAEGGMANSLSNQNLAWLPPPQGLTILEKVLGAQGEMGVFKPDWQNLAK QFPEFAKTHYFAAVIPSAEAVPPTASIFDKLINLEASQRADYLLDYLRRS VAQILKLEIEQIQSHDSLLDLGMDSLMIMEAIASLKQDLQLMLYPREIYE RPRLDVLTAYLAAEFTKAHDSEAATAAAAIPSQSLSVKTKKQWQKPDHKN PNPIAFILSSPRSGSTLLRVMLAGHPGLYSPPELHLLPFETMGDRHQELG LSHLGEGLQRALMDLENLTPEASQAKVNQWVKANTPIADIYAYLQRQAEQ RLLIDKSPSYGSDRHILDHSEILFDQAKYIHLVRHPYAVIESFTRLRMDK LLGAEQQNPYALAESIWRTSNRNILDLGRTVGADRYLQVIYEDLVRDPRK VLTNICDFLGVDFDEALLNPYSGDRLTDGLHQQSMGVGDPNFLQHKTIDP ALADKWRSITLPAALQLDTIQLAETFAYDLPQEPQLTPQTQSLPSMVERF VTVRGLETCLCEWGDRHQPLVLLLHGILEQGASWQLIAPQLAAQGYWVVA PDLRGHGKSAHAQSYSMLDFLADVDALAKQLGDRPFTLVGHSMGSIIGAM YAGIRQTQVEKLILVETIVPNDIDDAETGNHLTTHLDYLAAPPQHPIFPS LEVAARRLRQATPQLPKDLSAFLTQRSTKSVEKGVQWRWDAFLRTRAGIE FNGISRRRYLALLKDIQAPITLIYGDQSEFNRPADLQAIQAALPQAQRLT VAGGHNLHFENPQAIAQIVYQQLQTPVPKTQ

Nucleic Acids Encoding the PKS

The present invention provides recombinant nucleic acids that encode the PKSs of the invention. The recombinant nucleic acids include double-stranded and single-stranded DNAs and RNA derived therefrom. The recombinant nucleic acids of the invention include those that encode an open reading frame (ORF) of a PKS of the present invention. The recombinant nucleic acids of the invention also include, in a variety of embodiments, promoter sequences for transcribing the ORF in a suitable host cell. The recombinant nucleic acids of the invention include, in some embodiments, sequences sufficient for having the recombinant nucleic acid stably replicate in a host cell, such as sequences that provide a replicon capable of stable maintenance in a host cell or sequences that direct homologous recombination of the nucleic acid into a chromosome of the host cell. In some embodiments, the nucleic acid is a plasmid, including but not limited to plasmids containing an origin of replication. The present invention also provides vectors, such as expression vectors, comprising another recombinant nucleic acid of the present invention. The present invention provides host cell comprising any of the recombinant nucleic acids and/or capable of expressing a PKS of the present invention. In some embodiments, the host cell, when cultured under suitable conditions, is capable of producing an α-olefin of the invention.

It will be apparent to one of skill in the art that a variety of recombinant vectors can be utilized in the practice of the invention. As used herein, “vector” refers to polynucleotide elements that are used to introduce recombinant nucleic acid into cells for either expression or replication (or both). Selection and use of such vectors generally is routine in the art. An “expression vector” is a recombinant nucleic acid capable of expressing (producing proteins encoded by) DNA coding sequences (and corresponding mRNA) that are operatively linked with regulatory sequences, such as promoters. Thus, an expression vector refers to a recombinant DNA or RNA construct, such as a plasmid, a phage, a recombinant virus, or other vector that, upon introduction into an appropriate host cell that when cultured under appropriate conditions, results in expression of the DNA coding sequence. Appropriate expression vector elements suitable for use in accordance with the present invention are well known to those of skill in the art and include those that are replicable in eukaryotic cells and/or prokaryotic cells and those that remain episomal as well as those that integrate into the host cell genome.

The vectors of the invention include those chosen to contain control sequences operably linked to the resulting coding sequences in a manner that expression of the coding sequences may be effected in an appropriate host. Suitable control sequences include those that function in eukaryotic and prokaryotic host cells. If the cloning vectors employed to obtain PKS genes lack control sequences for expression operably linked to the PKS-encoding nucleotide sequences, the nucleotide sequences are inserted into appropriate expression vectors. This can be done individually, or using a pool of isolated encoding nucleotide sequences, which can be inserted into “host” vectors, the resulting vectors transformed or transfected into host cells, and the resulting cells plated out into individual colonies. Suitable control sequences for single cell cultures of various types of organisms are well known in the art. Control systems for expression in yeast are widely available and are routinely used. Control elements include promoters, optionally containing operator sequences, and other elements depending on the nature of the host, such as ribosome binding sites. Particularly useful promoters for prokaryotic hosts include those from PKS gene clusters that result in the production of polyketides as secondary metabolites, including those from Type I or aromatic (Type II) PKS gene clusters. Examples are act promoters, tcm promoters, spiramycin promoters, and the like. However, other bacterial promoters, such as those derived from the genes encoding sugar metabolizing enzymes, such as those that metabolize galactose, lactose (lac) and maltose, are also useful. Additional examples include promoters derived from the genes encoding biosynthetic enzymes such as those that encode the enzymes for tryptophan (tip) biosynthesis, the β-lactamase (bla) gene promoter, bacteriophage lambda PL promoter, and the T5 promoter. In addition, synthetic promoters, such as the tac promoter (U.S. Pat. No. 4,551,433; incorporated herein by reference), can be used to construct an expression vector of the invention.

As noted, particularly useful control sequences are those which themselves, or with suitable regulatory systems, activate expression during transition from growth to stationary phase in the vegetative mycelium. Illustrative control sequences, vectors, and host cells of these types include the modified Streptomyces coelicolor CH999 and vectors described in PCT publication No. WO 96/40968 and similar strains of Streptomyces lividans . See U.S. Pat. Nos. 5,672,491; 5,830,750; 5,843,718; and 6,177,262, each of which is hereby incorporated by reference. Other regulatory sequences may also be desirable; these include those that allow for regulation of expression of the PKS sequences relative to the growth of the host cell. Regulatory sequences are known to those of skill in the art, and examples include those which cause the expression of a gene to be turned on or off in response to a chemical or physical stimulus, including the presence of a regulatory compound. Other types of regulatory elements may also be present in the vector, for example, enhancer sequences.

Selectable markers can also be included in the recombinant expression vectors of the invention. A variety of markers are known that are useful in selecting for transformed cell lines; these generally are any gene whose expression confers a selectable phenotype on transformed cells when the cells are grown in an appropriate selective medium. Such markers include, for example, genes that confer antibiotic resistance or sensitivity to a host cell.

The various PKS nucleotide sequences, or a mixture of such sequences, can be cloned into one or more recombinant vectors as individual cassettes, with separate control elements or under the control of a single promoter. The PKS encoding subunits or components can include flanking restriction sites to allow for the easy deletion and insertion of other PKS encoding subunits. The design of such restriction sites is known to those of skill in the art and can be accomplished using the techniques described in the scientific literature, such as site-directed mutagenesis and PCR. Methods for introducing the recombinant vectors of the present invention into suitable hosts are known to those of skill in the art and include the use of CaCl 2 or other agents, such as other divalent cations, lipofection, DMSO, protoplast transformation, conjugation, and electroporation.

Host Cells Comprising the PKS

The present invention provides host cells comprising the recombinant nucleic acid and/or PKS of the present invention. In many embodiments, the host cell, when cultured, is capable of producing an α-olefin. The host cell can be a eukaryotic or a prokaryotic cell. Suitable eukaryotic cells include yeast cells, such as from the genus Saccharomyces, Candida , or Schizosaccharomyces . A suitable species from the genus Saccharomyces is Saccharomyces cerevisiae . A suitable species from the genus Schizosaccharomyces is Schizosaccharomyces pombe . Suitable prokaryotic cells include, but are not limited to, the gram negative Escherichia coli and the gram positive Streptomyces species, such as S. coelicolor and S. lividans.

The PKSs of the invention can be in a host cell, and can isolated and purified. The PKS can synthesize the α-olefin in vivo (in a host cell) or in vitro (in a cell extract or where all necessary chemical components or starting materials are provided). The present invention provides methods of producing the α-olefin using any of these in vivo or in vitro means.

In some embodiments of the invention, the host cell comprises a PKS which produces butadiene comprising a loading module comprising an acrylyl-ACP starter, such as a DEBS proprionyl-CoA specific loading domain which is modified to accept acrylyl-CoA, and one or more nucleic acids encoding and capable of expressing biosynthetic enzymes for synthesizing acrylyl-CoA from propionate (see FIG. 8 ). An example of a set of such enzymes is propionyl-CoA ligase (synthetase) (EC 6.2.1.17) and acyl-CoA dehydrogenase (mammalian) (EC 1.3.99.3), and functional variants thereof. In some embodiments, the host cell comprises a nucleic acid encoding and capable of expressing an enzyme, or functional variant thereof, capable of converting propionate into propionyl-CoA, and an enzyme, or functional variant thereof, capable of converting propionyl-CoA into acrylyl-CoA. An enzyme capable of converting propionate into propionyl-CoA is the propionyl-CoA ligase encoded by the prpE gene of Salmonella typhimurium . An enzyme capable of converting propionyl-CoA into acrylyl-CoA is the mammalian acyl-CoA dehydrogenase. A host cell comprising this system is provided with propionate, such as by exogenously feeding propionate to the host cell, or produces propionate endogenously.

The amino acid sequence of the propionyl-CoA ligase encoded by the prpE gene in Salmonella typhimurium (GenBank accession no. NP_459366) comprises:

The amino acid sequence of the acyl-CoA dehydrogenase of Mus musculus (GenBank accession no. Q07417) comprises:

In some embodiments, the host cell of the invention comprises a PKS which produces butadiene and comprises a loading module comprising an acrylyl-ACP starter, such as a DEBS proprionyl-CoA specific loading domain which is modified to accept acrylyl-CoA, and one or more nucleic acids encoding and capable of expressing biosynthetic enzymes for synthesizing acrylyl-CoA from pyruvate (see FIG. 9 ). An example of a set of such enzymes is lactate dehydrogenase (EC 6.2.1.17), lactate CoA transferase (EC 2.8.3.1), propionyl-CoA ligase (synthetase) (EC 6.2.1.17), and lactoyl-CoA dehydratase (EC 4.2.1.54), or functional variants thereof. In some embodiments, the host cell comprises one or more nucleic acids encoding and capable of expressing these four enzymes. A host cell comprising this system is provided with propionate and a suitable organic molecule that the host cell can directly or indirectly convert into a pyruvate, and these compounds are either exogenously fed to or produced by the host cell. For example, if the host cell is E. coli , a suitable organic molecule is glucose.

The amino acid sequence of the lactate dehydrogenase encoded by the ldhA gene of E. coli (GenBank accession no. CAQ31881) comprises:

The amino acid sequence of the lactate CoA transferase encoded by the pct gene of Clostridium proponicum (GenBank accession no. CAB77207) comprises:

The amino acid sequence of the lactoyl-CoA dehydratase encoded by the pct gene of Clostridium proponicum (GenBank accession no. CAB77206) comprises:

In some embodiments, the host cell of the invention comprises a PKS which produces butadiene and comprises a loading module comprising an acrylyl-ACP starter, such as a DEBS proprionyl-CoA specific loading domain which is modified to accept acrylyl-CoA, and one or more nucleic acids encoding and capable of expressing biosynthetic enzymes for synthesizing acrylyl-CoA from acetyl CoA (see FIG. 10 ). An example of a set of such enzymes is acetyl-CoA carboxylase (EC 6.4.1.2), malonyl-CoA reductase (EC 1.2.1.75), 3-hydroxypropionate:CoA ligase, and 3-hydroxypropionyl-CoA hydratase (EC 4.2.1.116), or functional variants thereof. In some embodiments, the host cell comprises one or more nucleic acids encoding and capable of expressing the four enzymes described. A host cell comprising this system can be engineered to produce increased titers of acetyl-CoA.

In some embodiments, the host cell of the invention comprises a PKS which produces butadiene and comprises a loading module comprising an acrylyl-ACP starter, such as a DEBS proprionyl-CoA specific loading domain which is modified to accept acrylyl-CoA, and one or more nucleic acids encoding and capable of expressing biosynthetic enzymes for synthesizing acrylyl-CoA from propionate (see FIG. 15 ). An example of a set of such enzymes is propionyl-CoA ligase (synthetase) (EC 6.2.1.17), lactoyl-CoA dehydratase (EC 4.2.1.54), lactate dehydrogenase (EC 6.2.1.17), lactate CoA transferase (EC 2.8.3.1), or functional variants thereof. A host cell comprising this system is provided with propionate, either by exogenous feeding or by endogenous production.

In some embodiments, the host cell of the invention comprises a PKS which produces 3-methyl-2,4-pentadienoic acid and comprises the modules shown in FIG. 12 including a loading module comprising an acrylyl-ACP starter, such as a DEBS proprionyl-CoA specific loading domain which is modified to accept acrylyl-CoA, and one or more nucleic acids encoding and capable of expressing biosynthetic enzymes for synthesizing acrylyl-CoA (see FIG. 12 ). There are several methods for enabling a host cell to synthesize acrylyl-CoA described above. 3-methyl-2,4-pentadienoic acid can be enzymatically, catalytically, or pyrolytically converted to isoprene.

Methods of Producing α-Olefins Using the PKS

The present invention provides a method of producing an α-olefin comprising: providing a host cell of the present invention, and culturing said host cell in a suitable culture medium such that the α-olefin is produced. The method can further comprise isolating said α-olefin from the host cell and/or the culture medium. The method can further comprise polymerizing the α-olefin to itself and/or any other suitable organic molecule(s), including but not limited to other compounds comprising a C—C double bond. A variety of methods for heterologous expression of PKS genes and host cells suitable for expression of these genes and production of polyketides are described, for example, in U.S. Pat. Nos. 5,843,718; 5,830,750 and 6,262,340; WO 01/31035, WO 01/27306, and WO 02/068613; and U.S. Patent Application Pub. Nos. 20020192767 and 20020045220; each of which is incorporated herein by reference.

The present invention provides for a composition comprising an α-olefin isolated from a host cell from which the α-olefin is produced, and trace residues and/or contaminants of the host cell. Such trace residues and/or contaminants include cellular material produced by the lysis of the host cell. The present invention also provides α-olefins in substantially pure form.

Certain α-olefins produced by the PKSs of the present invention can be used as fuels. In some embodiments of the invention, an α-olefin produced in accordance with the invention can be used as a “green” jet fuel. The α-olefin can be catalytically oligomerized, including but not limited to dimerized, and optionally purified. The resulting products can be dimerized again to yield a mixture of branched molecules that are then catalytically hydrogenated. For example, 1-butene produced by a PKS of the present invention can be catalytically dimerized and purified. The resulting octene products can be dimerized again to yield a mixture of branched C16 molecules that are then catalytically hydrogenated. Oligomers of butene have been validated by the US Navy as both jet and diesel fuel replacements (Harvey, 2011. Journal of Chemical Technology and Biotechnology 86(1): 2-9.). Additional benefit may come from making branched, or aromatic, α-olefins using the avermectin (or other) loading modules, as described herein.

Thus, among others, the present invention has one or more of the following advantages: (1) it reduces the dependence on oil for producing certain chemicals, and (2) it serves as a means of capture and sequestration of carbon from the atmosphere.

The invention having been described, the following examples are offered to illustrate and not limit the subject invention.

Constructs can be conveniently designed at the amino acid level and then, back translation and DNA synthesis, such as that offered commercially by service providers such as DNA 2.0, can be conducted to yield the desired nucleic acid, which may be optimized for expression in a particular host cell type. Subsequent plasmid assembly can be conducted using standard molecular biology techniques.