title: Structure and function of the xenobiotic substrate-binding site and location of a potential non-substrate-binding site in a class pi glutathione S-transferase.
abstract: Complex structures of a naturally occurring variant of human class pi glutathione S-transferase 1-1 (hGSTP1-1) with either S-hexylglutathione or (9R,10R)-9-(S-glutathionyl)-10-hydroxy-9, 10-dihydrophenanthrene [(9R,10R)-GSPhen] have been determined at resolutions of 1.8 and 1.9 A, respectively. The crystal structures reveal that the xenobiotic substrate-binding site (H-site) is located at a position similar to that observed in class mu GST 1-1 from rat liver (rGSTM1-1). In rGSTM1-1, the H-site is a hydrophobic cavity defined by the side chains of Y6, W7, V9, L12, I111, Y115, F208, and S209. In hGSTP1-1, the cavity is approximately half hydrophobic and half hydrophilic and is defined by the side chains of Y7, F8, V10, R13, V104, Y108, N204, and G205 and five water molecules. A hydrogen bond network connects the five water molecules and the side chains of R13 and N204. V104 is positioned such that the introduction of a methyl group (the result of the V104I mutation) disturbs the H-site water structure and alters the substrate-binding properties of the isozyme. The hydroxyl group of Y7 forms a hydrogen bond (3.2 A) with the sulfur atom of the product. There is a short hydrogen bond (2.5 A) between Y108 (OH) and (9R, 10R)-GSPhen (O5), indicating the hydroxyl group of Y108 as an electrophilic participant in the addition of glutathione to epoxides. An N-(2-hydroxethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) molecule is found in the cavity between beta2 and alphaI. The location and properties of this HEPES-binding site fit a possible non-substrate-binding site that is involved in noncompetitive inhibition of the enzyme.
authors.affiliation: ABL-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Maryland 21702, USA.
authors.forename: X
authors.initials: X
authors.lastname: Ji
authors.forename: M
authors.initials: M
authors.lastname: Tordova
authors.forename: R
authors.initials: R
authors.lastname: O'Donnell
authors.forename: J F
authors.initials: JF
authors.lastname: Parsons
authors.forename: J B
authors.initials: JB
authors.lastname: Hayden
authors.forename: G L
authors.initials: GL
authors.lastname: Gilliland
authors.forename: P
authors.initials: P
authors.lastname: Zimniak
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D018360:Crystallography, X-Ray; D005982:Glutathione Transferase / Q000737:chemistry* / Q000378:metabolism*; D006531:HEPES / Q000378:metabolism; D006801:Humans; D051379:Mice; D051381:Rats; D012997:Solvents; D055672:Static Electricity; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014867:Water; D015262:Xenobiotics / Q000378:metabolism*
chemical_list: D012997:Solvents; D015262:Xenobiotics; D014867:Water; D005982:Glutathione Transferase; D006531:HEPES