Acyltransferase polyketide

T. Nguyen et al.. Exploiting the mosaic structure of trans-acyltransferase polyketide synthases for natural product discovery and pathway dissection. Nat. Biotechnol. 26, 225-233 (2008)... 

J. Moldenhauer et al.. The final steps of bacillaene biosynthesis in Bacillus amyloUquefa-ciens FZB42 direct evidence for beta, gamma dehydration by a trans-acyltransferase polyketide synthase. Angew. Chem. Int. Ed. 49,1465-1467 (2010)... 

Petkovic, H., Lill, R.E., Sheridan, R.M. et al. (2003) A novel erythromycin, 6-desmethyl erythromycin D, made by substituting an acyltransferase domain of the erythromycin polyketide synthase. The Journal of Antibiotics, 56, 543. 

Ruan, X., Pereda, A., Stassi, D.L. et al. (1997) Acyltransferase domain substitutions in erythromycin polyketide synthase yield novel erythromycin derivatives. Journal of Bacteriology, 179, 6416. 

Reeves, C.D., Murli, S., Ashley, G.W. et al. (2001) Alteration of the substrate specificity of a modular polyketide synthase acyltransferase domain through site-specific mutations. Biochemistry, 40, 15464. 

Figure 21-11 Catalytic domains within three polypeptide chains of the modular polyketide synthase that forms 6-deoxyerythronolide B, the aglycone of the widely used antibiotic erythromycin. The domains are labeled as for fatty acid synthases AT, acyltransferase ACP, acyl carrier protein KS, 3-ketoacyl-ACP synthase KR, ketoreductase DH, dehydrase ER, enoylreductase TE, thioesterase. After Pieper et al.338 Courtesy of Chaitan Khosla.

RS Gokhale, J Lau, DE Cane, C Khosla. Functional orientation of the acyltransferase domain in a module of the erythromycin polyketide synthase. Biochemistry 37 2524-2528, 1998. 

J Lau, H Fu, DE Cane, C Khosla. Dissecting the role of acyltransferase domains of modular polyketide synthases in the choice and stereochemical fate of extender units. Biochemistry 38 1643-1651, 1999. 

Figure 5 Domain organization of the erythromycin polyketide synthase. Putative domains are represented as circles and the structural residues are ignored. Each module incorporates the essential KS, AT, and ACP domains, while all but one include optional reductive activities. AT, acyltransferase ACP, acyl carrier protein KS, (3-ketoacyl synthase KR, P-ketoacyl reductase DH, dehydratase ER, enoyl reductase TE, thioesterase.

FIGURE 19.4 Modular organization of the six modules (I—VI) of 6-deoxyerythronolide B synthase (DEBS) enzyme as derived from Saccharopolyspora erythraea. Enzyme activities are acyltransferases (AT), acyl carrier proteins (ACP), fi-ketoacyl-ACP synthases (KS), P-ketoreductases (KR), dehytratases (DH), enoyl reductases (ER), and thioesterases (TE). The TE-catalyzed release of the polyketide chain results in the formation of 6-dEB (70), 375 379 383... 

Reeves CD, Murli S, Ashley GW, Piagentini M, Hutchinson CR, McDaniel R (2001) Alteration of the Substrate Specificity of a Modular Polyketide Synthase Acyltransferase Domain Through Site-Specific Mutations. Biochemistry 40 15464... 

Type III PKSs are found widely among plants and bacteria. They consist of a homodimer ketosynthase that iteratively condenses malonyl-CoA to give relatively smaller aromatic polyketides than those discussed in the last section (Figure 10). Type III PKS differs from Type II PKS in two important aspects (1) the KS directly recraits mal-onyl-CoA in the absence of an acyltransferase or an AGP and (2) the KS active site catalyzes decarboxylative condensation and chain elongation, and also defines the regioselectivity of intramolecular cyclization. The relatively simple mode of chain assembly has made Type III PKSs attractive targets for engineered biosynthesis. 

According to the now widely accepted model of Katz and coworkers (Fig. 7), the loading acyltransferase (AT-L) domain at the NHj-terminal of DEBS 1 initiates the polyketide chain-building process by transferring the propionyl-CoA primer unit via the pantetheinyl residue of the first acyl carrier protein... 

Cheng YQ, Tang GL, Shen B. Type I polyketide synthase requiring a discrete acyltransferase for polyketide biosynthesis. Proc. Natl. Acad. Sci. U.S.A. 2003 100 3149-3154. 

Simunovic V, Zapp J, Rachid S, Krug D, Meiser P, Muller R. Myxovirescin A biosynthesis is directed by hybrid polyketide synthases/nonribosomal peptide synthetase, 3-hydroxy-3-methylglutaryl-CoA synthases, and trans-acting acyltransferases. ChemBioChem. 2006 7 1206-1220. 

Acyltransferase, found in fatty acid syntheases and polyketide syntheases, adds a malonyl group to the holo form of the ACP domain... 

Type II PKS complexes are comprised at a minimum of four types of subunits encoded by discrete open reading frames acyl carrier protein, ketosynthase a, ketosynthase p (also referred to as chain length factor ), and a malonyl CoA acyltransferase responsible for loading acyl-CoA extender units on to the acyl carrier protein subunit (34 Fig. 4). Additional subunits containing ketoreductase, cyclase, or aromatase activity may also occur in more complex type II synthases. Typically, the four core subunits (acyl carrier protein, ketosynthase a, ketosynthase p, and malonyl-CoA acyltransferase) participate in the iterative series of condensation reactions until a specified polyketide chain length is achieved, then folding and cyclization reactions yielding the final... 

Type III polyketide synthases (PKSs) generate a diverse array of natural products by condensing multiple acetyl units from malonyl-CoA to specific starter substrates (1,2). The homodimeric enzymes orchestrate a series of acyltransferase, decarboxylation, condensation, cyclization, and aromatizatidn reactions at two functionally independent active sites. Due to their ability to vary either the starter molecule or the type of cyclization and the number of condensations, they are, along with terpene synthases, one of the major generators of carbon skeleton diversity in plant secondary metabolites (i). Among the starter substrates used, benzoyl-CoA is a rare starter molecule. It is utilized by bacterial type I PKSs to form soraphen A, enterocin and the wailupemycins (4). in plants, benzoyl-CoA is the starter unit for two type III PKSs, benzophenone synthase (BPS) and biphenyl synthase (BIS), both of which were cloned in our laboratory. 

F/gwre J. Installation of alkyl branches into polyketides by (A) and (B) noniterative type I PKSs or (C) and (D) AT4ess PKSs. ( ), methyl group of S-adenosylmethionine origin ACP, acyl carrier protein AT, malonyl CoA specific acyltransferase ATmm methylmalonyl CoA-specific acyltransferase Tfno, methoxymalonyl ACP-specific acyltransferase KS, ketoacyl synthase MT, methyltransferase SAM, S-adenosylmethionine. 

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