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Chapter 9,423

Site-directed mutagenesis study on the roles of evolutionally conserved aspartic acid residues in human glutathione S-transferase P1-1

Kong, K.H.; Inoue, H.; Takahashi, K.

Protein Engineering 6(1): 93-99

1993


ISSN/ISBN: 0269-2139
PMID: 8433974
Accession: 009422769

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The evolutionary conserved aspartyl residues (Asp57, Asp98 and Asp152) in human glutathione S-transferase P1-1 were replaced with alanine by site-directed mutagenesis to obtain the mutants (D57A, D98A and D152A). The replacement of Asp98 with alanine resulted in a decrease of the affinity for S-hexyl-GSH-agarose, a 5.5-fold increase of the K-m-GSH and a 2.9-fold increase of the I-50 of S-hexyl-GSH for GSH-CDNB conjugation. Asp98 seems to participate in the binding of GSH through hydrogen bonding with the alpha-carboxylate of the gamma-glutamyl residue of GSH. The k-cat of D98A was 2.6-fold smaller than that of the wild-type, and the pK-a of the thiol group of GSH bound in D98A was apprx 0.8 pK units higher than those in the wild-type. Asp98 also seems to contribute to the activation of GSH to some extent. On the other hand, most of the kinetic parameters of D57A and D152A were similar to those of the wild-type. However, the thermostabilities of D57A and D152A were significantly lower than that of the wild-type. Asp57 and Asp152 seem to be important for maintaining the proper conformation of the enzyme.

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