title: 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.
authors.affiliation: Department of Medicinal Chemistry, Box 357610, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Larissa M
authors.initials: LM
authors.lastname: Balogh
authors.forename: Isolde
authors.initials: I
authors.lastname: Le Trong
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Kripps
authors.forename: Laura M
authors.initials: LM
authors.lastname: Shireman
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Stenkamp
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Bengt
authors.initials: B
authors.lastname: Mannervik
authors.forename: William M
authors.initials: WM
authors.lastname: Atkins
mesh_terms: D000447:Aldehydes / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity*; D055162:Biocatalysis; D020134:Catalytic Domain / Q000235:genetics; D018360:Crystallography, X-Ray; D005982:Glutathione Transferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D018384:Oxidative Stress / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity / Q000235:genetics
chemical_list: D000447:Aldehydes; D008024:Ligands; D011994:Recombinant Proteins; C484555:GSTA1 protein, human; D005982:Glutathione Transferase; C041116:leukotriene-C4 synthase; C027576:4-hydroxy-2-nonenal