Biosynthesis of alternative extender units via the CCR route and ..

The allyl moiety of the immunosuppressive agent FK506 is structurally unique among polyketides and critical for its potent biological activity. Here, we detail the biosynthetic pathway to allylmalonyl-coenzyme A (CoA), from which the FK506 allyl group is derived, based on a comprehensive chemical, biochemical, and genetic interrogation of three FK506 gene clusters. A discrete polyketide synthase (PKS) with noncanonical domain architecture presumably in coordination with the fatty acid synthase pathway of the host catalyzes a multistep enzymatic reaction to allylmalonyl-CoA via -2-pentenyl-acyl carrier protein. Characterization of this discrete pathway facilitated the engineered biosynthesis of novel allyl group-modified FK506 analogues, 36-fluoro-FK520 and 36-methyl-FK506, the latter of which exhibits improved neurite outgrowth activity. This unique feature of FK506 biosynthesis, in which a dedicated PKS provides an atypical extender unit for the main modular PKS, illuminates a new strategy for the combinatorial biosynthesis of designer macrolide scaffolds as well as FK506 analogues.

the biosynthesis of unusual extender units described ..

Biosynthesis of the Allylmalonyl-CoA Extender Unit for the FK506 Polyketide Synthase ..

carboxylase in the biosynthesis of the extender units.

(2R)-Methoxymalonyl-ACP, (2R)-hydroxymalonyl-ACP, and (2S)-aminomalonyl-ACP elongate a polyketide chain with methoxyacetyl, glycolyl, or glycyl units, respectively, with the substituents at the α-carbons (methoxyl, hydroxyl, and amino groups) conferring functionalities and hydrogen-bonding potential not available through the use of the CoA-linked extender units., While it has not been described as a PKS extender unit, another ACP-linked PKS precursor worthy of discussion is glyceryl-ACP, which incorporates a glycerol-derived three-carbon unit into a tetronate ring of polyketides known as acyltetronic acids. The occurrence and biosynthesis of these four precursors is discussed below.

Biosynthesis Polyketides are ..

The next class of PKS extender units differs from the CoA-linked extender units discussed above in that they are covalently tethered to the 4′-Ppant groups of holo-ACPs (). Also, unlike malonyl-CoA, (2S)-methylmalonyl-CoA, and (2S)-ethylmalonyl-CoA, these precursors are unique to polyketide biosynthesis, with the genes coding for their biosynthesis found within or flanking the associated biosynthetic gene clusters. Although they are not nearly as common as malonyl-CoA or (2S)-methylmalonyl-CoA extender units, they are becoming more prevalent as more natural product biosynthetic pathways are elucidated. Currently, they are all found in pathways involving modular type I PKSs, although future natural product discoveries may reveal their presence in other types of PKSs as well.

Biosynthesis of the allylmalonyl-CoA extender unit for the FK506 polyketide synthase proceeds ..
however, it seemed that the choice of extender units in polyketide biosynthesis was ..

Polyketide biosynthesis in many ..

Nature is providing a bountiful pool of valuable secondary metabolites, many of which possess therapeutic properties. However, the discovery of new bioactive secondary metabolites is slowing down, at a time when the rise of multidrug-resistant pathogens and the realization of acute and long-term side effects of widely used drugs lead to an urgent need for new therapeutic agents. Approaches such as synthetic biology are promising to deliver a much-needed boost to secondary metabolite drug development through plug-and-play optimized hosts and refactoring novel or cryptic bacterial gene clusters. Here, we discuss this prospect focusing on one comprehensively studied class of clinically relevant bioactive molecules, the polyketides. Extensive efforts towards optimization and derivatization of compounds via combinatorial biosynthesis and classical engineering have elucidated the modularity, flexibility and promiscuity of polyketide biosynthetic enzymes. Hence, a synthetic biology approach can build upon a solid basis of guidelines and principles, while providing a new perspective towards the discovery and generation of novel and new-to-nature compounds. We discuss the lessons learned from the classical engineering of polyketide synthases and indicate their importance when attempting to engineer biosynthetic pathways using synthetic biology approaches for the introduction of novelty and overexpression of products in a controllable manner.

Podevels AM, Kevany BM, Thomas MG (2009) Biosynthesis of polyketide synthase extender units…

as a polyketide synthase building block in the biosynthesis ..

The recent discovery of the new PKS extender units hydroxymalonyl- and aminomalonyl-ACP, haloethylmalonyl-CoAs, and 8 and the elucidation of their biosynthetic pathways has significantly expanded the pool of PKS building blocks to be used in the assembly of new polyketide scaffolds. The addition of a novel allylmalonyl PKS extender unit to the repertoire of PKS building blocks provides added potential for increasing the structural diversity of polyketides with a chemically tractable olefinic handle. The production of 1 from a 2-producing strain supplemented with 16 demonstrates the feasibility of biologically installing an allyl group onto other polyketide scaffolds.

21/07/2017 · Elucidation and exploitation of a crotonyl-CoA carboxylase/reductase-independent pathway for unusual polyketide extender unit biosynthesis


Research on the biosynthesis of PKS extender units is generously funded by the National Institutes of Health (AI065850) and by an Alfred Toepfer Faculty Fellow to M.G.T. We thank Elizabeth Felnagle for helpful comments. We thank Dr. Wendy L. Kelly (Georgia Institute of Technology) for sharing unpublished data.