Substrate specificity combined with stereopromiscuity in glutathione transferase A4-4-dependent metabolism of 4-hydroxynonenal.
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Balogh LM, Le Trong I, Kripps KA, Shireman LM, Stenkamp RE, Zhang W, Mannervik B, Atkins WM
Substrate specificity combined with stereopromiscuity in glutathione transferase A4-4-dependent metabolism of 4-hydroxynonenal.
Biochemistry. 2010 Feb 23;49(7):1541-8. doi: 10.1021/bi902038u.
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- 20085333 [ View in PubMed]
- 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.