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.
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.
Hu
X
X
Cancer Research Laboratory, Mercy Cancer Institute, Mercy Hospital of Pittsburgh, Pennsylvania 15219, USA.
O'Donnell
R
R
Srivastava
S K
SK
Xia
H
H
Zimniak
P
P
Nanduri
B
B
Bleicher
R J
RJ
Awasthi
S
S
Awasthi
Y C
YC
Ji
X
X
Singh
S V
SV
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism*; D001564:Benzo(a)pyrene / Q000378:metabolism; D001665:Binding Sites; D002273:Carcinogens / Q000378:metabolism*; D015870:Gene Expression; D005978:Glutathione / Q000378:metabolism*; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D011110:Polymorphism, Genetic; D011485:Protein Binding; D013237:Stereoisomerism
D002273:Carcinogens; D007527:Isoenzymes; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; D005978:Glutathione