Polyketide combinatorial biosynthesis

Staunton, J. and Wilkinson, B. (2001) Combinatorial biosynthesis of polyketides and nonribosomal peptides. Current Opinion in Chemical Biology, 5, 159. 

Weissman, K.J. and Leadlay, P.F. (2005) Combinatorial biosynthesis of reduced polyketides. Nature Reviews Microbiology, 3, 925. 

Khosla, C.Z.R. (1996) Generation of polyketide libraries via combinatorial biosynthesis. Trends in Biotechnology, 14, 335-341. 

In this chapter, we will introduce an exciting class of natural product biosynthetic enzymes, the modular synthases, as well as their associated enzyme partners. We will discuss the use of metabolic engineering as a tool for small-molecule discovery and development, both through directed fermentation and combinatorial biosynthesis. In addition, we will review six classes of partner enzymes involved in the modification of polyketide (PK) and nonribosomal peptide (NRP) natural products. We believe that these enzymatic transformations hold great opportunities for synthetic chemists and will serve as the foundation for a new trend in both discovery and process chemistry. 

The biosynthesis of many hydroxylated natural products proceeds through regio- and enantioselective modification of polyketides, which are assembled through chain elongation via acetate or propionate units [2]. The enzymes responsible for the chain elongation and subsequent reduction, elimination, aromatiza-tion, and further modifications are classified as polyketide synthases [3]. These multifunctional enzymes have been used for whole-cell biotransformation toward unnatural metabolites that are within the scope of combinatorial biosynthesis... 

Until the biosynthesis of aromatic polyketides can be controlled as precisely as modular PKSs, the most likely utility for this class of PKS is in the generation of libraries to screen for new activities. Due to the highly reactive nature of the aromatic polyketide backbones, a variety of cyclization patterns have been created through combinatorial biosynthesis with aromatic PKS gene clusters... 

Macrocyclic polyketides have so far been the primary focus of combinatorial biosynthesis technologies. The mutagenesis techniques outlined in Sec. VI sug-... 

J Staunton. Combinatorial biosynthesis of erythromycin and complex polyketides. Curr Opin Chem Biol 2 339-345, 1998. 

CJ Tsoi, C Khosla. Combinatorial biosynthesis of unnatural natural products the polyketide example. Chem Biol 2 355-362, 1995. 

One new wrinkle on the combinatorial strategy involves a process referred to as combinatorial biosynthesis. In this situation, bacterial gene expression is altered in the hope of changing the structure and function of specific enzymes. For example, one class of potential bacteria-derived drugs are the polyketides, which may have antibiotic, immunosuppressant, and anticancer activity. Bacteria produce polyketides with the help of a family of enzymes known as polyketide synthases (PKSs). To date, most of the normally produced polyketides screened have shown little activity. 

By the methods presented for the combinatorial biosynthesis of polyketides, a multitude of modified and artificial polyketide substances should be available. New antibiotics, potentially with fewer side effects and consequently broader applicability, are desperately needed in the light of increasing resistance of bacteria towards established medications. 

Figure 4.22 Combinatorial biosynthesis manipulation of the aromatic polyketide pathway.

Manipulation of the biosynthetic pathways leading to natural compounds, so-called combinatorial biosynthesis, is presented in the third section, with particular attention paid to the opportunities arising from polyketide biosynthesis. Finally, combinatorial biotransformation of natural or synthetic compounds by means of isolated enzymes or whole microorganisms is presented in the fourth section. 

Polyketides (PKs) are a typical example of a large and diverse class of NPs that derive from several related biosynthetic pathways. Their stmctures contain repeating units iteratively assembled into a range of diverse chemical structures (Fig. 10.43). PKs can be taken as an example of the application of combinatorial biosynthesis as both the... 

Figure 10.43 Combinatorial biosynthesis structures of naturally occurring polyketides.

Bentley R, Bennett JW (1999) Constmcting Polyketides from Collie to Combinatorial Biosynthesis. Annu Rev Microbiol 53 411... 

Kantola J, Kunnari T, Mantsala P, Ylihonkoa K (2003) Expanding the Scope of Aromatic Polyketides by Combinatorial Biosynthesis. Comb Chem High Throughput Screen 6 501... 

Weissman KJ, Leadlay PE (2005) Combinatorial Biosynthesis of Reduced Polyketides. Nat Rev Microbiol 3 925... 

The power of combinatorial biosynthesis has been best demonstrated through the engineered biosynthesis of polyketides." Polyketides consist of a structurally diverse family of natural products and are mostly biosynthesized by soil-bome actinomyces as secondary metabolites. Fungi and plants have also been sources of polyketides. 

Uncovering the biochemical principles governing these mechanisms is therefore important for the rational biosynthesis of lovastatin and other fungal polyketides. It will also allow the enzymatic components of iterative PKSs to be used as tools in the combinatorial biosynthesis of entirely new polyketide scaffolds. 

Figure 9 Aromatic polyketides synthesized by combinatorial biosynthesis...

Weissman KJ, Leadlay PF. Combinatorial biosynthesis of reduced polyketides. Nat. Rev. Microbiol. 2005 3 925-936. 

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