Engineering a Carbonyl Reductase for High-Efficiency Synthesis of Optically Pure (<i>S</i>)-Pro-Xylane: An Alternative Synthetic Route

Pro-Xylane is a biologically active <i>C-</i>glycoside compound in cosmetic products. The conventional method involves converting d-xylose from beech trees to 1-<i>C-</i>(β-d-xylopyranosyl)-acetone and reducing it with sodium borohydride. This method produced borate salts as byproducts, requiring a tedious removal process. In addition, (<i>S</i>)-Pro-Xylane shows superior biological activity compared to (<i>R</i>)-Pro-Xylane. Hence, with focus on the second step of the reduction reaction, the carbonyl reductase (CR) from <i>Candida orthopsilosis</i> Co 90-125 (CoCR13) was engineered in this study. Variant R129E/D210F showed a 245.33-fold improvement in <i>k</i>_cat/<i>K</i>_m over the wild-type (WT) with >99% (β, <i>S</i>) diastereomeric excess. The reaction achieved a spatiotemporal yield of 49.97 g·L^-1·h^-1 with a 1300 mM substrate. Molecular dynamics simulations suggest that mutations on R129 and D210 increased the proportion of productive substrate binding states and resulted in a shorter and wider tunnel. This study expands the utilization of CR for the alternative and sustainable production of (<i>S</i>)-Pro-Xylane.