Description

The proto-oncogene IDH1, isocitrate dehydrogenase 1, is a gene that provides enzymes the ability to break down fats for energy and protect cells. In the normal wild-type oxidative decarboxylation reaction, isocitrate produces alpha-ketoglutarate, with the reactant NADP+ being converted to NADPH. However, mutant IDH1 can catalyze a neomorphic reduction, the NADPH-dependent reduction of alpha-ketoglutarate to D-2-hydroxyglutarate, D2HG, which can competitively inhibit alpha ketoglutarate-dependent enzymes. We hope to investigate the catalytic efficiency of the enzyme to discover the relationship between kinetics and tumor phenotypes. We have previously shown that the mutation R132Q produces high levels of D2HG while still being able to produce alpha-ketoglutarate, unlike other mutants. Furthermore, we previously solved a crystal structure of R132Q with the mutant bound to isocitrate and NADP+ substrates under reducing conditions to stimulate the cellular environment. This crystal structure led to the discovery of the reducing agent, TCEP, forming an adduct with NADP+. The impact of this adduct on the catalytic activity of the mutant R132Q IDH1 is unknown. We hypothesize that the NADP+-dependent normal reaction will be inhibited due to the unavailability of the NADP+ substrate. We have conducted steady-state kinetic assays on R132Q mutant at varying concentrations of reducing agents to determine the impact of the TCEP-NADP adduct on R132Q catalysis. We show that observed rates of R132Q decrease as reducing agent concentrations increase, with different reducing agents having unique tendencies for inhibition. This project can reveal possible precautions for researchers to be aware of when crystallizing IDH1 and performing catalytic reactions, as well as help us clarify mechanisms of catalysis.