Discovery of a novel inhibitor of NAD(P)+-dependent malic enzyme (ME2) by high-throughput screening
Aim:Malic enzymes are oxidative decarboxylases with NAD+ or NAD(P)+ as cofactor that catalyze the conversion of L-malate to pyruvate and CO2. The aim of this study was to discover and characterize a potent inhibitor of human NAD(P)+-dependent malic enzyme 2 (ME2).Methods:Recombinant human ME2-His-Tag fusion protein was overexpressed in E coli and purified with Ni-NTA resin. A high-throughput screening (HTS) assay was developed to find ME2 inhibitors. Detergent Brij-35 was used to exclude false positives. The characteristics of the inhibitor were analyzed with enzyme kinetics analysis. A thermal shift assay for ME2 was carried out to verify the binding of the inhibitor with the enzyme.Results:An HTS system for discovering ME2 inhibitors was established with a Z′ factor value of 0.775 and a signal-to-noise ratio (S/N) of 9.80. A library containing 12 683 natural products was screened. From 47 hits, NPD387 was identified as an inhibitor of ME2. The primary structure-activity relationship study on NPD387 derivatives showed that one derivative NPD389 was more potent than the parent compound NPD387 (the IC50 of NPD389 was 4.63±0.36 μmol/L or 5.59±0.38 μmol/L, respectively, in the absence or presence of 0.01% Brij-35 in the assay system). The enzyme kinetics analysis showed that NPD389 was a fast-binding uncompetitive inhibitor with respect to the substrate NAD+ and a mixed-type inhibitor with respect to the substrate L-malate.Conclusion:NPD389 is a potent ME2 inhibitor that binds to the enzyme in a fast-binding mode, acting as an uncompetitive inhibitor with respect to the substrate NAD+ and a mixed-type inhibitor with respect to the substrate L-malate.