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Substrate specificity combined with stereopromiscuity in glutathione transferase A4-4-dependent metabolism of 4-hydroxynonenal.

ABSTRACT: Conjugation to glutathione (GSH) by glutathione transferase A4-4 (GSTA4-4) is a major route of elimination for the lipid peroxidation product 4-hydroxynonenal (HNE), a toxic compound that contributes to numerous diseases. Both enantiomers of HNE are presumed to be toxic, and GSTA4-4 has negligible stereoselectivity toward them, despite its high catalytic chemospecificity for alkenals. In contrast to the highly flexible, and substrate promiscuous, GSTA1-1 isoform that has poor catalytic efficiency with HNE, GSTA4-4 has been postulated to be a rigid template that is preorganized for HNE metabolism. However, the combination of high substrate chemoselectivity and low substrate stereoselectivity is intriguing. The mechanism by which GSTA4-4 achieves this combination is important, because it must metabolize both enantiomers of HNE to efficiently detoxify the biologically formed mixture. The crystal structures of GSTA4-4 and an engineered variant of GSTA1-1 with high catalytic efficiency toward HNE, cocrystallized with a GSH-HNE conjugate analogue, demonstrate that GSTA4-4 undergoes no enantiospecific induced fit; instead, the active site residue Arg15 is ideally located to interact with the 4-hydroxyl group of either HNE enantiomer. The results reveal an evolutionary strategy for achieving biologically useful stereopromiscuity toward a toxic racemate, concomitant with high catalytic efficiency and substrate specificity toward an endogenously formed toxin.

SUBMITTER: Balogh LM

PROVIDER: S-EPMC2829664 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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Substrate specificity combined with stereopromiscuity in glutathione transferase A4-4-dependent metabolism of 4-hydroxynonenal.

Balogh Larissa M LM Le Trong Isolde I Kripps Kimberly A KA Shireman Laura M LM Stenkamp Ronald E RE Zhang Wei W Mannervik Bengt B Atkins William M WM

Biochemistry 20100201 7

Conjugation to glutathione (GSH) by glutathione transferase A4-4 (GSTA4-4) is a major route of elimination for the lipid peroxidation product 4-hydroxynonenal (HNE), a toxic compound that contributes to numerous diseases. Both enantiomers of HNE are presumed to be toxic, and GSTA4-4 has negligible stereoselectivity toward them, despite its high catalytic chemospecificity for alkenals. In contrast to the highly flexible, and substrate promiscuous, GSTA1-1 isoform that has poor catalytic efficienc ...[more]

PMID: 20085333

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Project description:Human glutathione transferase A4-4 (hGSTA4-4) displays high catalytic efficiency towards 4-hydroxyalkenals and other cytotoxic and mutagenic products of radical reactions and lipid peroxidation. Its role as a target for the chemosensitization of cancer cells has not been investigated so far. In this study, the inhibitory potency of twelve selected natural products and ten monocarbonyl curcumin derivatives against hGSTA4-4 was studied. Among natural products, ellagic acid turned out to be the strongest inhibitor with an IC50 value of 0.44 ± 0.01 μM. Kinetic analysis using glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB) as variable substrates showed that ellagic acid behaved as a competitive inhibitor towards both GSH and CDNB, with Ki values of 0.39 ± 0.02 and 0.63 ± 0.03 μM, respectively. Among the curcumin derivatives studied, three proved to be the most potent inhibitors, in the order DM151 > DM101 > DM100, with IC50 values of 2.4 ± 0.1 μM, 12.7 ± 1.1 μΜ and 16.9 ± 0.4 μΜ, respectively. Further kinetic inhibition analysis of the most active derivative, DM151, demonstrated that this compound is a mixed inhibitor towards CDNB with inhibition constants of Ki = 4.1 ± 0.5 μM and Ki' = 0.536 ± 0.034 μM, while it is a competitive inhibitor towards GSH with a Ki = 0.98 ± 0.11 μM. Molecular docking studies were performed to interpret the differences in binding of ellagic acid and curcumin derivatives to hGSTA4-4. The in silico measured docking scores were consistent with the obtained experimental data. Hydrogen bonds appear to be the main contributors to the specific binding of monocarbonyl curcumin derivatives, while π-π stacking interactions play a key role in the enzyme-ellagic acid interaction. In vitro cytotoxicity assessment of the worst (DM148) and the best (DM151) inhibitors was performed against glioblastoma cell lines U-251 MG and U-87 MG. The results revealed that DM151 displays considerably higher cytotoxicity against both glioblastoma cell lines, while the glioblastoma cytotoxicity of DM148 was very limited. Furthermore, low and non-toxic doses of DM151 sensitized U-251 MG cells to the first-line glioblastoma chemotherapeutic temozolomide (TMZ), allowing us to propose for the first time that hGSTA4-4 inhibitors may be attractive therapeutic partners for TMZ to optimize its clinical effect in glioblastoma chemotherapy.

Dataset Information

Substrate specificity combined with stereopromiscuity in glutathione transferase A4-4-dependent metabolism of 4-hydroxynonenal.

Publications

Substrate specificity combined with stereopromiscuity in glutathione transferase A4-4-dependent metabolism of 4-hydroxynonenal.

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