The role of conformational flexibility in Baeyer-Villiger monooxygenase catalysis and structure.

ABSTRACT

BACKGROUND: The Baeyer-Villiger monooxygenases (BMVOs) are a group of microbial enzymes that have garnered interest as industrial biocatalysts. While great strides have been made in recent years to understand the mechanism of these enzymes from a structural perspective, our understanding remains incomplete. In particular, the role of a twenty residue loop (residues 487-504), which we refer to as the "Control Loop," that is observed in either an ordered or disordered state in various crystal structures remains unclear. METHODS: Using SAXS, we have made the first observations of the Loop in solution with two BVMOs, cyclohexanone monooxygenase (CHMO) and cyclopentadecanone monooxygenase. We also made a series of mutants of CHMO and analyzed them using SAXS, ITC, and an uncoupling assay. RESULTS: These experiments show that Control Loop ordering results in an overall more compact enzyme without altering global protein foldedness. We have also demonstrated that the Loop plays a critical and complex role on enzyme structure and catalysis. The Control Loop appears to have a direct impact on the organization of the overall structure of the protein, as well as in influencing the active site environment. CONCLUSIONS: The data imply that the Loop can be divided into two regions, referred to as "sub-loops," that coordinate overall domain movements to changes in the active site. GENERAL SIGNIFICANCE: A better understanding of the mechanistic role of the Control Loop may ultimately be helpful in designing mutants with altered specificity and improved catalytic efficiency.