Regioselectivity Switching in CYP107Pdh-Catalyzed VD3 Hydroxylation: A Structure-Guided Approach To Improve Calcidiol Production

The biocatalytic production of 25-hydroxyvitamin D3 (25(OH)VD3, calcidiol) represents a superior alternative to traditional chemical synthesis. However, the reported VD3 hydroxylases generally exhibit suboptimal catalytic efficiency, limiting their practical applications. In this study, a cytochrome P450 CYP107Pdh from Pseudonocardia dioxanivorans_CB1190, which displays unique C26 hydroxylation activity on VD3, was identified. Then, structure-guided loop engineering combined with binding pocket reshaping was conducted on CYP107Pdh, leading to the generation of the quintuple variant 89_90insIP/T112A/V161L/G186V (M4). This variant shifted the regioselectivity from 91% C26 in the wild type (WT) to 81% C25 for calcidiol production. In addition, variant M4 showed a remarkable enhancement in catalytic activity, achieving a catalytic efficiency (kcat/Km) that is 75-fold higher than that of the WT. Computational analyses revealed that the regioselectivity shift and activity improvement are primarily attributed to a conformational transition in the substrate-binding pocket from an open to a more closed state, which optimizes substrate binding and facilitates efficient 25-hydroxylation of VD3. Finally, a semipreparative biotransformation yielded 2.64 g of crystalline calcidiol (95% purity) from a 1-L reaction, thereby expanding the enzyme library of VD3 hydroxylases and underscoring its potential for industrial-scale production of calcidiol.