Discovery of a new NADPH-dependent aldo-keto reductase from Candida orthopsilosis catalyzing the stereospecific synthesis of (R)-pantolactone by genome mining.

(R)-Pantolactone (PL) is a key chiral intermediate for the synthesis of calcium (R)-pantothenate and (R)-panthenol used as food additives. The commercial production of (R)-pantothenate is performed by the resolution of racemic pantothenate, which is synthesized through an aldol condensation and a cyanation reaction. In this study, we investigated another synthetic method of (R)-pantothenate through the stereoselective reduction of ketopantoyl lactone (KPL) by aldo-keto reductase (AKR). A series of conjugated polyketone reductases (CPRs) were discovered from GenBank database by genome mining approach. The putative CPR gene from Candida orthopsilosis Co 90-125 (CorCPR) was cloned and functionally expressed in Escherichia coli BL21 (DE3). The optimum pH and temperature of recombinant CorCPR were 6.0-7.0 and 40 ℃, respectively. The K and v toward KPL were1.3 mM and 227.3 μmol/min/mg protein, respectively. The conserved sequences suggest that CorCPR belongs to AKR3C family of AKR superfamily. Furthermore, a catalytic tetrad was proposed, and the detailed mechanism was clarified by molecular docking. In a batch reaction, 50 mM KPL was reduced to (R)-PL with 99% conversion and > 99% enantiomeric excess within 5 h. The recombinant CorCPR from C. orthopsilosis shows potential application in the asymmetric synthesis of (R)-pantothenate preparation.