Linked Life Data

9930979

Source:http://linkedlifedata.com/resource/pubmed/id/9930979

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
1999-2-19
pubmed:databankReference
pubmed:abstractText
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:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jan
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
26
pubmed:volume
38
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1193-202
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed-meshheading:9930979-Amino Acid Sequence, pubmed-meshheading:9930979-Amino Acid Substitution, pubmed-meshheading:9930979-Binding Sites, pubmed-meshheading:9930979-Catalytic Domain, pubmed-meshheading:9930979-Cloning, Molecular, pubmed-meshheading:9930979-Crystallography, X-Ray, pubmed-meshheading:9930979-DNA Primers, pubmed-meshheading:9930979-Escherichia coli, pubmed-meshheading:9930979-Glutathione Transferase, pubmed-meshheading:9930979-Histidine, pubmed-meshheading:9930979-Humans, pubmed-meshheading:9930979-Kinetics, pubmed-meshheading:9930979-Macromolecular Substances, pubmed-meshheading:9930979-Molecular Sequence Data, pubmed-meshheading:9930979-Mutagenesis, Site-Directed, pubmed-meshheading:9930979-Polymerase Chain Reaction, pubmed-meshheading:9930979-Protein Conformation, pubmed-meshheading:9930979-Recombinant Fusion Proteins, pubmed-meshheading:9930979-Sequence Alignment
pubmed:year
1999
pubmed:articleTitle
Functions of His107 in the catalytic mechanism of human glutathione S-transferase hGSTM1a-1a.
pubmed:affiliation
Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.