1tdi

From Proteopedia

Crystal Structure of hGSTA3-3 in Complex with Glutathione

Overview

The crystal structure of human class alpha glutathione (GSH) S-transferase, A3-3 (hGSTA3-3) in complex with GSH was determined at 2.4 A. Despite, considerable amino acid sequence identity with other human class alpha, GSTs (e.g., hGSTA1-1), hGSTA3-3 is unique due to its exceptionally high, steroid double bond isomerase activity for the transformation of, Delta(5)-androstene-3,17-dione (Delta(5)-AD) to, Delta(4)-androstene-3,17-dione. A comparative analysis of the active, centers of hGSTA1-1 and hGSTA3-3 reveals that residues in positions 12 and, 208 may contribute to their disparate isomerase activity toward, Delta(5)-AD. Substitution of these two residues of hGSTA3-3 with the, corresponding residues in hGSTA1-1 followed by kinetic characterization of, the wild-type and the mutant enzymes supported this prediction. On the, basis of our model of the hGSTA3-3.GSH.Delta(5)-AD ternary complex and, available biochemical data, we propose that the thiolate group of, deprotonated GSH (GS(-)) serves as a base to initiate the reaction by, accepting a proton from the steroid and the nonionized hydroxyl group of, catalytic residue Y9 (HO-Y9) functions as part of a proton-conducting wire, to transfer a proton back to the steroid. Residue R15 may function to, stabilize the deprotonated thiolate group of GSH (GS(-)), and a GSH-bound, water molecule may donate a hydrogen bond to the 3-keto group of, Delta(5)-AD and thus help the thiolate of GS(-) to initiate the proton, transfer and the subsequent stabilization of the reaction intermediate.

About this Structure

1TDI is a Single protein structure of sequence from Homo sapiens with GSH as ligand. Active as Glutathione transferase, with EC number 2.5.1.18 Full crystallographic information is available from OCA.

Reference

Crystal structure of human glutathione S-transferase A3-3 and mechanistic implications for its high steroid isomerase activity., Gu Y, Guo J, Pal A, Pan SS, Zimniak P, Singh SV, Ji X, Biochemistry. 2004 Dec 21;43(50):15673-9. PMID:15595823

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