Three-dimensional structure, catalytic properties, and evolution of a sigma class glutathione transferase from squid, a progenitor of the lens S-crystallins of cephalopods
| Autor: | E. C. Van Rosenvinge, Gary L. Gilliland, W. W. Johnson, S. I. Tomarev, J. Piatigorsky, Richard N. Armstrong, Xinhua Ji |
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| Rok vydání: | 1995 |
| Předmět: |
Models
Molecular Multiple isomorphous replacement Dimer Molecular Sequence Data Biology Crystallography X-Ray Polymerase Chain Reaction Biochemistry Protein Structure Secondary Substrate Specificity chemistry.chemical_compound Crystallin Lens Crystalline Animals Amino Acid Sequence Enzyme kinetics DNA Primers Glutathione Transferase chemistry.chemical_classification Binding Sites Base Sequence Sequence Homology Amino Acid Decapodiformes Protein primary structure Active site Glutathione Biological Evolution Crystallins Invertebrates Isoenzymes Kinetics Enzyme chemistry Vertebrates biology.protein Digestive System |
| Zdroj: | Biochemistry. 34:5317-5328 |
| ISSN: | 1520-4995 0006-2960 |
| Popis: | The glutathione transferase from squid digestive gland is unique in its very high catalytic activity toward 1-chloro-2,4-dinitrobenzene and in its ancestral relationship to the genes encoding the S-crystallins of the lens of cephalopod eye. The three-dimensional structure of this glutathione transferase in complex with the product 1-(S-glutathionyl)-2,4-dinitrobenzene (GSDNB) has been solved by multiple isomorphous replacement techniques at a resolution of 2.4 A. Like the cytosolic enzymes from vertebrates, the squid protein is a dimer. The structure is similar in overall topology to the vertebrate enzymes but has a dimer interface that is unique when compared to all of the vertebrate and invertebrate structures thus far reported. The active site of the enzyme is very open, a fact that appears to correlate with the high turnover number (800 s-1 at pH 6.5) toward 1-chloro-2,4-dinitrobenzene. Both kcat and kcat/KmCDNB exhibit pH dependencies consistent with a pKa for the thiol of enzyme-bound GSH of 6.3. The enzyme is not very efficient at catalyzing the addition of GSH to enones and epoxides. This particular characteristic appears to be due to the lack of an electrophilic residue at position 106, which is often found in other GSH transferases. The F106Y mutant enzyme is much improved in catalyzing these reactions. Comparisons of the primary structure, gene structure, and three-dimensional structure with class alpha, mu, and pi enzymes support placing the squid protein in a separate enzyme class, sigma. The unique dimer interface suggests that the class sigma enzyme diverged from the ancestral precursor prior to the divergence of the precursor gene for the alpha, mu, and pi classes. |
| Databáze: | OpenAIRE |
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