Enhancing Catalytic Activity of a Baeyer–Villiger monooxygenase from Oceanicola granulosus: Simultaneous Engineering of the Distal Site and Active Site

Enzymatic synthesis of δ-lactones using Baeyer–Villiger monooxygenases (BVMOs) has potential in the fragrance and flavor industries but is constrained by poor activity toward ortho-alkyl-substituted cyclopentanones, key δ-lactone precursors. We determined the crystal structure of a BVMO derived from Oceanicola granulosus (OgBVMO), uncovering a unique loop adjacent to key catalytic residue R335. Site-saturation mutagenesis of loop residues A338 and A339 identified the A339E variant, obtaining a 2.4- to 3-fold increase in catalytic activity toward ortho-alkyl-substituted cyclopentanones (2-methyl-, 2-ethyl-, 2-hexyl-, and 2-heptylcyclopentanone). Further engineering the substrate-binding pocket yielded the Q442N variant, improving activity by 2.7–3.8-fold. Remarkably, the combinatorial mutant A339E/Q442N achieved 3.3–5.2-fold higher activity than the wild-type. Molecular dynamics simulations indicated that these improvements were driven by more favorable nucleophilic attack distances, underscoring the synergistic effects of distal and active-site mutations. These findings offer valuable insights into enhancing the catalytic activity of BVMOs, supporting the green manufacturing of high-value flavor compounds.