Active site architecture of polymorphic forms of human glutathione S-transferase P1-1 accounts for their enantioselectivity and disparate activity in the glutathione conjugation of 7beta,8alpha-dihydroxy-9alpha,10alpha-ox y-7,8,9,10-tetrahydrobenzo(a)pyrene

Biochem Biophys Res Commun. 1997 Jun 18;235(2):424-8. doi: 10.1006/bbrc.1997.6777.

Abstract

In this study, we demonstrate that the active site architecture of the human glutathione (GSH) S-transferase Pi (GSTP1-1) accounts for its enantioselectivity in the GSH conjugation of 7beta,8alpha-dihydroxy-9alpha,10alpha-oxy-7,8,9, 10-tetrahydrobenzo(a) pyrene (anti-BPDE), the ultimate carcinogen of benzo(a)pyrene. Furthermore, we report that the two polymorphic forms of human GSTP1-1, differing in their primary structure by a single amino acid in position 104, have disparate activity toward (+)-anti-BPDE, which can also be rationalized in terms of their active site structures. When concentration of (+)-anti-BPDE, which among four BPDE isomers is the most potent carcinogen, was varied and GSH concentration was kept constant at 2 mM (saturating concentration), both forms of hGSTP1-1 [hGSTP1-1(V104) and hGSTP1-1(I104)] obeyed Michaelis-Menten kinetics. The V(max) of GSH conjugation of (+)-anti-BPDE was approximately 3.4-fold higher for hGSTP1-1(V104) than for hGSTP1-1(I104). Adherence to Michaelis-Menten kinetics was also observed for both isoforms when (-)-anti-BPDE, which is a weak carcinogen, was used as the variable substrate. However, (-)-anti-BPDE was a relatively poor substrate for both isoforms as compared with (+)-anti-BPDE. Moreover, there were no significant differences between hGSTP1-1(V104) and hGSTP1-1(I104) in either V(max) or K(m) for (-)-anti-BPDE. The mechanism of differences in kinetic properties and enantioselectivity of hGSTP1-1 variants toward anti-BPDE was investigated by modeling of the two proteins with conjugation product molecules in their active sites. Molecular modeling studies revealed that the differences in catalytic properties of hGSTP1-1 variants as well as the enantioselectivity of hGSTP1-1 in the GSH conjugation of anti-BPDE can be rationalized in terms of the architecture of their active sites. Our results suggest that the population polymorphism of hGSTP1-1 variants with disparate enzyme activities may, at least in part, account for the differential susceptibility of individuals to carcinogens such as anti-BPDE and possibly other similar carcinogens.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / metabolism*
  • Benzo(a)pyrene / metabolism
  • Binding Sites
  • Carcinogens / metabolism*
  • Gene Expression
  • Glutathione / metabolism*
  • Glutathione S-Transferase pi
  • Glutathione Transferase / chemistry*
  • Glutathione Transferase / genetics
  • Glutathione Transferase / metabolism*
  • Humans
  • Isoenzymes / chemistry*
  • Isoenzymes / genetics
  • Isoenzymes / metabolism*
  • Kinetics
  • Models, Molecular
  • Molecular Conformation
  • Polymorphism, Genetic
  • Protein Binding
  • Stereoisomerism

Substances

  • Carcinogens
  • Isoenzymes
  • Benzo(a)pyrene
  • 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide
  • GSTP1 protein, human
  • Glutathione S-Transferase pi
  • Glutathione Transferase
  • Glutathione