Structural Basis of the Suppressed Catalytic Activity of Wild-type Human Glutathione Transferase T1-1 Compared to Its W234r Mutant.
From: Department of Cell and Molecular Biology, Uppsala University, Biomedical Centre, Box 590, SE-751 24, Uppsala, Sweden. kaspars@xray.bmc.uu.se
Journal of molecular biology
- Publish Date: Jan 2006
- ISSN: 0022-2836
- Volume: 355
- Issue: 1
- Pages: 96-105
- Medium: Print
- Language: English
- Citation (JAMA): Tars Kaspars, Larsson Anna-Karin, Shokeer Abeer, et al. Structural Basis of the Suppressed Catalytic Activity of Wild-type Human Glutathione Transferase T1-1 Compared to Its W234r Mutant.. J. Mol. Biol. Jan 2006;355:96-105
Abstract
The crystal structures of wild-type human theta class glutathione-S-transferase (GST) T1-1 and its W234R mutant, where Trp234 was replaced by Arg, were solved both in the presence and absence of S-hexyl-glutathione. The W234R mutant was of interest due to its previously observed enhanced catalytic activity compared to the wild-type enzyme. GST T1-1 from rat and mouse naturally contain Arg in position 234, with correspondingly high catalytic efficiency. The overall structure of GST T1-1 is similar to that of GST T2-2, as expected from their 53% sequence identity at the protein level. Wild-type GST T1-1 has the side-chain of Trp234 occupying a significant portion of the active site. This bulky residue prevents efficient binding of both glutathione and hydrophobic substrates through steric hindrance. The wild-type GST T1-1 crystal structure, obtained from co-crystallization experiments with glutathione and its derivatives, showed no electron density for the glutathione ligand. However, the structure of GST T1-1 mutant W234R showed clear electron density for S-hexyl-glutathione after co-crystallization. In contrast to Trp234 in the wild-type structure, the side-chain of Arg234 in the mutant does not occupy any part of the substrate-binding site. Instead, Arg234 is pointing in a different direction and, in addition, interacts with the carboxylate group of glutathione. These findings explain our earlier observation that the W234R mutant has a markedly improved catalytic activity with most substrates tested to date compared to the wild-type enzyme. GST T1-1 catalyzes detoxication reactions as well as reactions that result in toxic products, and our findings therefore suggest that humans have gained an evolutionary advantage by a partially disabled active site.
Mesh Headings (Keywords): Binding Sites, Catalysis, Crystallography, X-Ray, Glutathione, Glutathione Transferase, Humans, Mutation, Missense, Protein Conformation
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