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FUNCTIONAL SIGNIFICANCE OF A NATURAL ALLELIC VARIANT OF HUMAN CARBONYL REDUCTASE 3 (CBR3)

Department of Pharmaceutical Sciences, State University of New York at Buffalo, Buffalo, New York (S.S.L., J.G.B.); Department of Structural Biology, Hauptman-Woodward Medical Research Institute, Buffalo, New York, (D.G.); Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, New York (D.G.); and Therapeutics Program, Roswell Park Cancer Institute, Buffalo, New York (D.G., J.G.B.)

Human carbonyl reductase (CBR) activity accounts for a significant fraction of the metabolism of endogenous and xenobiotic carbonyl compounds. It is possible that genetic polymorphisms in CBR1 and CBR3 are key for the wide interindividual variability in the disposition of CBR drug substrates. We pinpointed a single nucleotide polymorphism in CBR3 (CBR3 V244M) that encodes for a V244 to M244 change. Blacks showed a higher frequency of the M244 allele (q = 0.51, n = 49) than did whites (q = 0.31, n = 70; p = 0.003). In addition, DNA variation panels from 10 ethnic groups presented a wide range of CBR3 V244M genotype distributions. Kinetic experiments with the recombinant CBR3 protein variants and menadione revealed that CBR3 M244 has significantly higher V_max than does CBR3 V244 (V_max CBR3 M244 = 40.6 ± 1.3 µmol/min · mg versus V_max CBR3 V244 = 19.6 ± 2.0 µmol/min · mg, p = 0.002). In contrast, both isoforms presented similar K_m values (K_m CBR3 M244 = 22.9 ± 2.9 µM versus K_m CBR3 V244 = 24.6 ± 3.2 µM, p = 0.43). Assays with NADP(H) demonstrated a higher V_maxNADP(H) (1.6-fold) and increased catalytic efficiency (V_maxNADP(H)/K_mNADP(H)) for CBR3 M244 compared with CBR3 V244 (p = 0.013). Comparative three-dimensional analyses based on the structure of the homologous porcine carbonyl reductase suggested that the V244M substitution is positioned in a region critical for interactions with the NADP(H) cofactor. These studies demonstrate that the common CBR3 V244M polymorphism encodes for CBR3 isoforms with distinctive enzymatic properties.

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