Type III Polyketide Synthases: Current State and Perspectives

Abstract

Microorganisms produce an array of secondary metabolites primarily for their growth, self-defense, communication, and survival in natural environments. Among several other microbial secondary metabolites, antibiotic (antimicrobial, antiviral, and antifungal activities) compound effects are vital for humans and other higher living organisms to combat pathogens. Even though several such antibiotic compounds are identified in the past decades, very few have been commercialized and made available for practical applications. Polyketides are secondary metabolites that are produced as a result of enzyme-catalyzed condensation/polymerization reactions of simple fatty acids resulting in products with diverse structural and functional properties. The enzymes involved in the production of polyketides are polyketide synthases (PKSs), which are mainly involved in condensation of acyl-thioester units into functional secondary metabolites. Based on the origin and structural diversity, PKSs are classified as type I PKSs, type II PKSs, and type III PKSs. Type I PKSs are large multifunctional proteins with multi-domain architecture and are mostly of fungal origin, whereas type II PKSs are mono-functional proteins predominantly present in bacteria and actinomycetes. Type III PKSs are primarily of plant origin, and very few have been reported from microbial sources. In this chapter, the occurrence and distribution of type III PKSs, the genetic architecture of the genes involved in type III polyketide biosynthesis, the protein structure of type III PKSs, and the commercial importance of type III PKSs are discussed in detail.