Structure-Function Analysis of the Extended Conformation of a Polyketide Synthase Module

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Assembly-line polyketide synthases (PKS) are large multi-enzyme complexes.
• PKS modules have been observed in distinct conformations, including 'extended' and 'arch-shaped' architectures.
• The catalytic relevance of these different PKS conformations remained unestablished.

Purpose of the Study:

• To determine the catalytic competence of the extended conformation of a PKS module.
• To investigate the functional significance of PKS module architecture.

Main Methods:

• Utilized a fully human naïve antigen-binding fragment (Fab) library to isolate a high-affinity antibody targeting the extended PKS conformation.
• Verified the antibody-bound conformation using X-ray crystallography and SEC-SAXS.
• Performed kinetic analyses to assess catalytic activity.

Main Results:

• A high-affinity antibody specifically bound to the extended conformation of a PKS module.
• Structural analyses confirmed the antibody-stabilized extended conformation.
• Kinetic studies demonstrated that this conformation is fully competent for intermodular chain translocation, intramodular chain elongation, and functional group modification.

Conclusions:

• The extended conformation of a PKS module is catalytically active and competent for all its essential enzymatic functions.
• This study establishes the functional relevance of the extended PKS module architecture in polyketide biosynthesis.