Polyketide synthase domains

What mechanisms are utilized for incorporation of double bonds into fatty acids Propose a mechanism that makes use of polyketide synthase domains (Fig. 21-11) in the synthesis of polyunsaturated fatty acids. See Metz et al.356... 

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. 

Del Vecchio, F., Petkovic, H., Kendrew, S.G. et al. (2003) Active-site residue, domain and module swaps in modular polyketide synthases. Journal of Industrial Microbiology Biotechnology, 30, 489. 

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. 

Gokhale, R.S., Hunziker, D., Cane, D.E. and Khosla, C. (1999) Mechanism and specificity of the terminal thioesterase domain from the erythromycin polyketide synthase. Chemistry Biology, 6, 117. 

Lu, H., Tsai, S.-C., Khosla, C. and Cane, D.E. (2002) Expression, site-directed mutagenesis, and steady state kinetic analysis of the terminal thioesterase domain of the methymycin/picromycin polyketide synthase. Biochemistry, 41, 12590-12597. 

Boddy, C.N., Schneider, T.L., Hotta, K. et al. (2003) Epothilone C macrocyclization and hydrolysis are catalyzed by the isolated thioesterase domain of epothilone polyketide synthase. Journal of the American Chemical Society, 125, 3428-3429. 

Phosphopantetheine tethering is a posttranslational modification that takes place on the active site serine of carrier proteins - acyl carrier proteins (ACPs) and peptidyl carrier proteins (PCPs), also termed thiolation (T) domains - during the biosynthesis of fatty acids (FAs) (use ACPs) (Scheme 23), polyketides (PKs) (use ACPs) (Scheme 24), and nonribosomal peptides (NRPs) (use T domain) (Scheme 25). It is only after the covalent attachment of the 20-A Ppant arm, required for facile transfer of the various building block constituents of the molecules to be formed, that the carrier proteins can interact with the other components of the different multi-modular assembly lines (fatty acid synthases (FASs), polyketide synthases (PKSs), and nonribosomal peptide synthetases (NRPSs)) on which the compounds of interest are assembled. The structural organizations of FASs, PKSs, and NRPSs are analogous and can be divided into three broad classes the types I, II, and III systems. Even though the role of the carrier proteins is the same in all systems, their mode of action differs from one system to another. In the type I systems the carrier proteins usually only interact in cis with domains to which they are physically attached, with the exception of the PPTases and external type II thioesterase (TEII) domains that act in trans. In the type II systems the carrier proteins selectively interact... 

Recently, bacterial NRPS modules with the organization of A-KR-PCP have been discovered in the valino-mycin and cereulide synthetases. The A domains of these modules selectively activate a-keto acids. After the resulting adenylate is transferred to the PCP domain, the a-ketoacyl- -PCP intermediate is reduced to a PCP-bound, a-hydroxythioester by the KR domain. These domains use NAD(P)H as a cofactor and are inserted into A domains between two conserved core motifs analogous to MT domains. Their substrate specificity differs from that of polyketide synthase KR domains, which reduce /3-ketoacyl substrates. Similar fungal NRPSs, such as beauvericin synthetase, utilize A domains that selectively activate a-hydroxy acids. These molecules are thought to be obtained using an in trans KR domain, which directly reduces the necessary, soluble a-keto acid. 

Figure 10 N M R structural analysis of carrier domains. Three conformations of the PCP domain from tyrocidine synthetase (brown box) and the NMR structure of the related AGP domain from a polyketide synthase. The star symbol signifies the position of the conserved phosphopantetheinylated serine residue. The protein ribbon representations are rainbow colored from red (N-terminus) to violet. PDB codes A/H state, 2GDW H-state, 2GDX A-state, 2GDY AGP, 2AF8.

Bingle, L. E. H., Simpson, T. J., and Lazarus, C. M. (1999). Ketosynthase domain probes identify two subclasses of fungal polyketide synthase genes. Fungal Genet. Biol. 26, 209-223. 

Preisig-Mueller, R. et al.. Plant polyketide synthases leading to stilbenoids have a domain catalyzing malonyl-CoA C02 exchange, malonyl-CoA decarboxylation, and covalent enzyme modification and a site for chain lengthening. Biochemistry, 36, 8349, 1997. 

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 Chuck, M McPherson, H Huang, JR Jacobsen, C Khosla, DE Cane. Molecular recognition of diketide substrates by a (3-ketoacyl-ACP synthase domain within a bimodular polyketide synthase. Chem Biol 4 757-766, 1997. 

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. 

IE Holzbaur, RC Harris, M Bycroft, J Cortes, C Bisang, J Staunton, BAM Rudd, PF Leadlay. Molecular basis of Celmer s rules the role of two ketoreductase domains in the control of chirality by the erythromycin modular polyketide synthase. Chem Biol 6 189-195, 1999. 

J Cortes, KEH Wiesmann, GA Roberts, MJB Brown, J Staunton, PF Leadlay. Repositioning of a domain in a modular polyketide synthase to promote specific chain cleavage. Science 268 1487-1489, 1995. 

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 9 Construction of bimodular polyketide synthases, (a) Chromosomal repositioning of the thioesterase domain from the C-terminus of module 6 to the end of module 2 in the erythromycin PKS leads to production of triketide lactones and the disruption of erythromycin biosynthesis, (b) DEBS 1-TE contains a fusion within the ACP domains of modules 2 and 6. In Saccharopolyspora erythraea and Streptomyces coelicolor the construct produced both propionate and acetate-derived lactones, (c) DEBS 1+TE contains a fusion between ACP2 and the thioesterase domain. In S. coelicolor, the protein biosynthesized the same lactones.

RJX Zawada, C Khosla. Domain analysis of the molecular recognition features of an aromatic polyketide synthase. J Biol Chem 272 16184-16188, 1997. 

SF Haydock, JF Aparicio, I Molnar, T Schwecke, LE Khaw, A Konig, AFA Marsden, IS Galloway, J Staunton, PF Leadlay. Divergent sequence motifs correlated with the substrate specificity of (methyl)malonyl-CoA acyl carrier protein trans-acylase domains in modular polyketide synthases. FEBS Lett 374 246-248, 1995. 

M Oliynyk, MJB Brown, J Cortes, J Staunton, PF Leadlay. A hybrid modular polyketide synthase obtained by domain swapping. Chem Biol 3 833-839, 1996. 

CM Kao, M McPherson, R McDaniel, El Fu, DE Cane, C Khosla. Alcohol stereochemistry in polyketide backbones is controlled by the 3-ketoreductase domains of modular polyketide synthases. J Am Chem Soc 120 2478-2479, 1998. 

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