Polyketide synthase modules

Chen AY, Cane DE, Khosla C (2007) Structure-Based Dissociation of a Type I Polyketide Synthase Module. Chem Biol 14 784... 

Wu, N., Tsuji, S.Y., Cane, D.E. Khosla, C. Assessing the balance between protein-protein interactions and enzyme-substrate interactions in the channeling of intermediates between polyketide synthase modules. J. Am. Chem. Soc. 123, 6465-6474 (2001). 

S. Tsuji, D. Cane, C. Khosla, Selective protein-protein interactions direct the channeling of intermediates between polyketide synthase modules, Biochemistry 2001, 40, 2326-2331. 

Hu Z, Bao K, Zhou X, Zhou Q, Hopwood DA, Kieser T, Deng Z. Repeated polyketide synthase modules involved in the biosynthesis of a heptaene macrolide by Sneptomyces sp. FR-008. Mol Microbiol 1994 14 163-172. 

The Raps modules have a high degree of homology, the most striking instances of which are the extremely conserved ketosynthase domains (69). There is some sequence diversity, however, in the acyltransfeiase domains. It has been reported that this diversity reflects the specificity of the acyl transferase for an acetate or propionate extender unit (22). It has also been observed that the N-terminus of each multienzyme has a potential atnphipachic domain, which may encourage dimerization of the polyketide synthase modules into catalytically active hotnodimers (69,70). 

K. Watanabe, C.C.C. Wang, C.N. Boddy, D.E. Cane, C. Khosla, Understanding substrate specificity of polyketide synthase modules by generating hybrid multimodular synthases. J. Biol. Chem. 278, 42020-42026 (2003)... 

J.R. Whicher et al.. Structural rearrangements of a polyketide synthase module during its catalytic cycle. Nature 510, 560-564 (2014)... 

Will it be possible to use individual dehydrogenase modules from large assemblies such as polyketide synthases ... 

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. 

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. 

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. 

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.

To the extent that they are covalently linked, the complex polyketide synthases are less reliant on association for function. In most systems, however, transient docking between multienzymes is required. Recently, it has been demonstrated that the regions of sequence upstream from N-terminal modules and downstream from C-terminal modules (referred to as interpolypeptide linkers) play a crucial role in the assembly of functional modules in vivo [78]. Clearly, the presence of such linkers will also be important for productive biosynthesis in vitro using multiprotein systems. 

Polyketides are made by the sequential activity of domains of large, multifunctional enzymes called polyketide synthases (PKSs) (Fig. 6a and b). Polyketides are formed by the condensation and modification of acyl units derived from acyl-CoA precursors. Domains are organized in modules and each module carries out the series of steps necessary for one cycle of polyketide chain elongation. A single protein can have more than one module, and several different proteins together can make up a PKS. The number of modules determines the size of the polyketide. A growing polyketide chain is tethered to the enzyme as a thiol ester and moves sequentially from the N- to the C-terminus of a module, lengthened by two carbon units per module. The first module in a PKS... 

The molecular backbone of the antibiotic erythromycin A [6-desoxy-erythronolide B (3)] is built up repetitively from one propionyl-coenzyme A (1) and six methyl-malonyl-coenzyme A (2) constituents by the action of polyketide-synthase, which itself consists of three proteins (DEBS 1 -3) (Schemes 1 and 2). Each protein contains two modules with several separate, cat-alytically active domains. In the first section, DEBS 1 carries an additional loading zone, and DEBS 3 contains a thioesterase in the final segment, catalyzing the decoupling of the product by building the lactone ring [6],... 

Such modifications of single modules open up the possibility of generating structural diversity using designed unnatural organisms to synthesize the desired polyketides. The synthesis of new structures, however, depends decisively on the substrate tolerance of the enzymes that follow upon the modified segments in the polyketide-synthases. 

Del Vecchio F, Petkovic H, Kendrew SG, Low L, Wilkinson B, Lill R, Cortes J, Rudd BA, Staunton J, Leadlay PF (2003) Active-Site Residue, Domain and Module Swaps in Modular Polyketide Synthases. J Ind Microbiol Biotechnol 30 489... 

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