Primary Citation of Related Structures: 3GTU, 4GTU
PubMed Abstract:
The hGSTM3 subunit, which is preferentially expressed in germ-line cells, has the greatest sequence divergence among the human mu class glutathione S-transferases. To determine a structural basis for the catalytic differences between hGSTM3-3 and other mu class enzymes, chimeric proteins were designed by modular interchange of the divergent C-terminal domains of hGSTM3 and hGSTM5 subunits ...
The hGSTM3 subunit, which is preferentially expressed in germ-line cells, has the greatest sequence divergence among the human mu class glutathione S-transferases. To determine a structural basis for the catalytic differences between hGSTM3-3 and other mu class enzymes, chimeric proteins were designed by modular interchange of the divergent C-terminal domains of hGSTM3 and hGSTM5 subunits. Replacement of 24 residues of the C-terminal segment of either subunit produced chimeric enzymes with catalytic properties that reflected those of the wild-type enzyme from which the C-terminus had been derived. Deletion of the tripeptide C-terminal extension found only in the hGSTM3 subunit had no effect on catalysis. The crystal structure determined for a ligand-free hGSTM3 subunit indicates that an Asn212 residue of the C-terminal domain is near a hydrophobic cluster of side chains formed in part by Ile13, Leu16, Leu114, Ile115, Tyr119, Ile211, and Trp218. Accordingly, a series of point mutations were introduced into the hGSTM3 subunit, and it was indeed determined that a Y119F mutation considerably enhanced the turnover rate of the enzyme for nucleophilic aromatic substitution reactions. A more striking effect was observed for a double mutant (Y119F/N212F) which had a k(cat)/K(m)(CDNB) value of 7.6 x 10(5) s(-)(1) M(-)(1) as compared to 4.9 x 10(3) s(-)(1) M(-)(1) for the wild-type hGSTM3-3 enzyme. The presence of a polar Asn212 in place of a Phe residue found in the cognate position of other mu class glutathione S-transferases, therefore, has a marked influence on catalysis by hGSTM3-3.
Related Citations:
Crystal Structure of Human Class Mu Glutathione Transferase Gstm2-2. Effects of Lattice Packing on Conformational Heterogeneity Raghunathan, S., Chandross, R.J., Kretsinger, R.H., Allison, T.J., Penington, C.J., Rule, G.S. (1994) J Mol Biol 238: 815
Cloning, Expression, and Characterization of a Class-Mu Glutathione Transferase from Human Muscle, the Product of the Gst4 Locus Vorachek, W.R., Pearson, W.R., Rule, G.S. (1991) Proc Natl Acad Sci U S A 88: 4443
A Distinct Human Testis and Brain Mu-Class Glutathione S-Transferase. Molecular Cloning and Characterization of a Form Present Even in Individuals Lacking Hepatic Type Mu Isoenzymes Campbell, E., Takahashi, Y., Abramovitz, M., Peretz, M., Listowsky, I. (1990) J Biol Chem 265: 9188
Organizational Affiliation:
Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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