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 PHA,10-ALPHA-OXY-7,8,9,10-TETRAHYDROBENZO(A)PYRENE

In this study, we demonstrate that the active site architecture of the human glutathione (GSH) S-transferase Pi (GSTP1-1) accounts for its e nantioselectivity in the GSH conjugation of 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-oxy-7,8,9,10-tetrahydrobenzo(a) pyrene (anti-BPDE), th e ultimate carcinogen of benzo(a)pyrene. Furthermore, we report that t he two polymorphic forms of human GSTP1-1, differing in their primary structure by a single amino acid in position 104, have disparate activ ity toward (+)-anti-BPDE, which can also be rationalized in terms of t heir active site structures. When concentration of (+)-anti-BPDE, whic h among four BPDE isomers is the most potent carcinogen, was varied an d GSH concentration was kept constant at 2 mM (saturating concentratio n), both forms of hGSTP1-1 [hGSTP1-1(V104) and hGSTP1-1(I104)] obeyed Michaelis-Menten kinetics. The V-max of GSH conjugation of (+)-anti-BP DE was approximately 3.4 fold higher for hGSTP1-1(V104) than for hGSTP 1-1(I104). Adherence to Michaelis-Menten kinetics was also observed fo r both isoforms when (-)-anti-BPDE, which is a weak carcinogen, was us ed as the variable substrate. However, (-)-anti-BPDE was a relatively poor substrate for both isoforms as compared with (+)-anti-BPDE. Moreo ver, 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 p roteins with conjugation product molecules in their active sites. Mole cular modeling studies revealed that the differences in catalytic prop erties of hGSTP1-1 variants as well as the enantioselectivity of hGSTP 1-1 in the GSH conjugation of anti-BPDE can be rationalized in terms o f the architecture of their active sites. Our results suggest that the population polymorphism of hGSTP1-1 variants with disparate enzyme ac tivities may, at least in part, account for the differential susceptib ility of individuals to carcinogens such as anti-BPDE and possibly oth er similar carcinogens. (C) 1997 Academic Press.