Determinants of specificity for aflatoxin B1-8,9-epoxide in alpha-class glutathione S-transferases

Biochem J. 1999 Apr 1;339 ( Pt 1)(Pt 1):95-101.

Abstract

We have used homology modelling, based on the crystal structure of the human glutathione S-transferase (GST) A1-1, to obtain the three-dimensional structures of rat GSTA3 and rat GSTA5 subunits bound to S-aflatoxinyl-glutathione. The resulting models highlight two residues, at positions 208 and 108, that could be important for determining, either directly or indirectly, substrate specificity for aflatoxin-exo-8,9-epoxide among the Alpha-class GSTs. Residues at these positions were mutated in human GSTA1-1 (Met-208, Leu-108), rat GSTA3-3 (Glu-208, His-108) and rat GSTA5-5 (Asp-208, Tyr-108): in the active rat GSTA5-5 to those in the inactive GSTA1-1; and in the inactive human GSTA1-1 and rat GSTA3-3 to those in the active rat GSTA5-5. These studies show clearly that, in all three GSTs, an aspartate residue at position 208 is a prerequisite for high activity in aflatoxin-exo-8,9-epoxide conjugation, although this alone is not sufficient; other residues in the vicinity, particularly residues 103-112, are important, perhaps for the optimal orientation of the aflatoxin-exo-8,9-epoxide in the active site for catalysis to occur.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aflatoxin B1 / analogs & derivatives*
  • Aflatoxin B1 / metabolism
  • Amino Acid Sequence
  • Animals
  • Catalysis
  • Glutathione Transferase / chemistry
  • Glutathione Transferase / genetics
  • Glutathione Transferase / metabolism*
  • Humans
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis
  • Rats
  • Sequence Homology, Amino Acid
  • Substrate Specificity

Substances

  • aflatoxin B1-2,3-oxide
  • Aflatoxin B1
  • Glutathione Transferase