Reconstitution of a Highly Reducing Type II PKS System Reveals 6π-Electrocyclization Is Required for o-Dialkylbenzene Biosynthesis

J Am Chem Soc. 2021 Feb 24;143(7):2962-2969. doi: 10.1021/jacs.0c13378. Epub 2021 Feb 12.

Abstract

Natural products containing an o-dialkylbenzene moiety exhibit a wide variety of bioactivities, including antibacterial, antifungal, antitumor, and antiangiogenic activities. However, the biosynthetic scheme of the o-dialkylbenzene moiety remains unclear. In this study, we identified the biosynthetic gene cluster (BGC) of compounds 1 and 2 in Streptomyces sp. SANK 60404, which contains a rare o-dialkylbenzene moiety, and successfully reconstituted the biosynthesis of 1 using 22 recombinant enzymes in vitro. Our study established a biosynthetic route for the o-tolyl group within the o-dialkylbenzene moiety, where the triene intermediate 3 loaded onto a unique acyl carrier protein (ACP) is elongated by a specific ketosynthase-chain length factor pair of a type II polyketide synthase system with the aid of a putative isomerase to be termed "electrocyclase" and a thioesterase-like enzyme in the BGC. The C2-elongated all-trans diketo-triene intermediate is subsequently isomerized to the 6Z configuration by the electrocyclase to allow intramolecular 6π-electrocyclization, followed by coenzyme FAD/FMN-dependent dehydrogenation. Bioinformatics analysis showed that the key genes are all conserved in BGCs of natural products containing an o-dialkylbenzene moiety, suggesting that the proposed biosynthetic scheme is a common strategy to form o-dialkylbenzenes in nature.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acyl Carrier Protein / genetics
  • Acyl Carrier Protein / metabolism
  • Anti-Bacterial Agents / biosynthesis
  • Anti-Bacterial Agents / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Benzene / chemistry*
  • Biological Products / chemistry
  • Biological Products / metabolism*
  • Cyclization
  • Multigene Family
  • Polyketide Synthases / genetics
  • Polyketide Synthases / metabolism*
  • Streptomyces / metabolism

Substances

  • Acyl Carrier Protein
  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Biological Products
  • Polyketide Synthases
  • Benzene