1GTU

LIGAND-FREE HUMAN GLUTATHIONE S-TRANSFERASE M1A-1A

Summary for 1GTU

• Entry DOI: 10.2210/pdb1gtu/pdb
• Descriptor: GLUTATHIONE S-TRANSFERASE (2 entities in total)
• Functional Keywords: transferase, glutathione, conjugation, detoxification, cytosolic, dimer
• Biological source: Homo sapiens (human)
• Cellular location: Cytoplasm: P09488
• Total number of polymer chains: 4
• Total formula weight: 102462.58

Authors

Patskovsky, Y.V.,Patskovska, L.N.,Listowsky, I. (deposition date: 1998-06-11, release date: 1999-02-02, Last modification date: 2024-05-22)

Primary citation

Patskovsky, Y.V.,Patskovska, L.N.,Listowsky, I.
Functions of His107 in the catalytic mechanism of human glutathione S-transferase hGSTM1a-1a.
Biochemistry, 38:1193-1202, 1999

PubMed Abstract: Domain interchange analyses and site-directed mutagenesis indicate that the His107 residue of the human subunit hGSTM1 has a pronounced influence on catalysis of nucleophilic aromatic substitution reactions, and a H107S substitution accounts for the marked differences in the properties of the homologous hGSTM1-1 (His107) and hGSTM4-4 (Ser107) glutathione S-transferases. Reciprocal replacement of His107 and Ser107 in chimeric enzymes results in reciprocal conversion of catalytic properties. With 1-chloro-2, 4-dinitrobenzene as a substrate, the His107 residue primarily influences the pH dependence of catalysis by lowering the apparent pKa of kcat/Km from 7.8 for the Ser107-containing enzymes to 6.3 for the His107-containing enzymes. There is a parallel shift in the pKa for thiolate anion formation of enzyme-bound GSH. Y6F mutations have no effect on the pKa for these enzymes. Crystal structures of hGSTM1a-1a indicate that the imidazole ring of His107 is oriented toward the substrate binding cleft approximately 6 A from the GSH thiol group. Thus, His107 has the potential to act as a general base in proton transfer mediated through an active site water molecule or directly following a modest conformational change, to promote thiolate anion formation. All wild-type enzymes and H107S chimera have nearly identical equilibrium constants for formation of enzyme-GSH complexes (Kd values of 1-2 x 10(-)6 M); however, KmGSH and Ki values for S-methylglutathione inhibition determined by steady-state kinetics are nearly 100-fold higher. The functions of His107 of hGSTM1a-1a are unexpected in view of a substantial body of previous evidence that excluded participation of histidine residues in the catalytic mechanisms of other glutathione S-transferases. Consequences of His107 involvement in catalysis are also substrate-dependent; in contrast to 1-chloro-2,4-dinitrobenzene, for the nucleophilic addition reaction of GSH to ethacrynic acid, the H107S substitution has no effect on catalysis presumably because product release is rate-limiting.

PubMed: 9930979
DOI: 10.1021/bi982164m

Experimental method

X-RAY DIFFRACTION (2.68 Å)