Polyketide synthase

PKS Overview

Anthracycline aglycone biosyn1

Polyketide synthase (PKS) is a multienzyme complex responsible for the biosynthesis of polyketides, a large family of metabolites with diverse structures and functions. These natural products have significant roles in organismal interactions and have been extensively utilized in medicine, agriculture, and industry. Polyketides include important antibiotics such as erythromycin, antifungals like amphotericin B, anticancer agents such as doxorubicin, and immunosuppressants like tacrolimus.

Types of Polyketide Synthases

Polyketide synthases are classified into three main types based on their structure and mechanism of action:

• Type I PKSs are large, multidomain enzymes that function in an assembly line fashion, where each domain carries out a specific reaction in the synthesis of the polyketide chain. They are further divided into modular and iterative subtypes.
• Type II PKSs consist of a set of discrete, monofunctional enzymes that work together in a cyclic manner to produce aromatic polyketides.
• Type III PKSs are homodimeric enzymes that catalyze the condensation of malonyl-CoA units to produce a variety of polyketides, often with simpler structures compared to those produced by Type I and II PKSs.

Biosynthesis

The biosynthesis of polyketides involves the sequential addition of two-carbon units, typically derived from acetyl-CoA or malonyl-CoA, to a growing polyketide chain. The process is catalyzed by PKS enzymes through a series of Claisen condensation reactions. The variability in polyketide structures is achieved by the action of various enzymes that modify the polyketide backbone through processes such as reduction, cyclization, and oxidation.

Biological Significance and Applications

Polyketides play crucial roles in the survival and competitiveness of producing organisms, serving as toxins, pigments, pheromones, and antibiotics. In humans, polyketide-derived drugs are used to treat a wide range of diseases, highlighting the importance of understanding PKS enzymes for drug discovery and development.

Challenges and Future Directions

The complexity of PKS enzymes and the intricacies of their regulation and expression pose significant challenges for the biosynthesis and engineering of polyketides. Advances in genetic engineering, synthetic biology, and bioinformatics are paving the way for the rational design and production of novel polyketides with desired properties.