(S)-specific carbonyl reductase from Candida parapsilosis ATCC 7330 as a model for the initial screening of inhibitors for human carbonyl reductase

Human carbonyl reductase (CBR1) reduces carbonyl groups in drug molecules, particularly anticancer drugs, leading to altered pharmacological effects. This study reports a simple and efficient system that utilizes enzymes isolated from yeast as a model for the initial screening of inhibitors for human carbonyl reductases, offering a viable process for large scale applications. A purified stereospecific enzyme, (S)-specific carbonyl reductase from Candida parapsilosis ATCC 7330 (SRED), was employed whose crystal structure, PDB ID: 3CTM (100% sequence identity with SRED) showed 27% similarity with CBR1 (PDB ID: 1WMA). Furthermore, it was found to have a similarity for reaction with isatin and inhibition with quercetin (non-competitive) as in CBR1. Isatin as substrate showed a Km of 5.3±1.08 mM, and Ki of 15.2±1.64 µM for quercetin as inhibitor. Using (S)-specific carbonyl reductase model enzyme, a novel inhibitor, ethyl (E)-4-(4-chlorophenyl)-2-oxobut-3-enoate (ECOB) was identified. ECOB showed mixed inhibition for isatin reduction, with a Ki of 14.87±0.78 µM and KI of 5.02±0.02 µM respectively. Circular dichroism and molecular modelling studies supported the inhibitor studies. ECOB showed a lower IC50 value of 7.2 µM, as compared to the standard inhibitor quercetin (11.7 µM), hence a better inhibitor than quercetin.