Residue R216 and Catalytic Efficiency of a Murine Class Alpha Glutathione S-Transferase toward Benzo[a]pyrene 7(R),8(S)-Diol 9(S),10(R)-Epoxide
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- 作者：Yijun Gu ; Shivendra V. Singh ; and Xinhua Ji
- 刊名：Biochemistry
- 出版年：2000
- 出版时间：October 17, 2000
- 年：2000
- 卷：39
- 期：41
- 页码：12552 - 12557
- 全文大小：510K
- 年卷期：v.39,no.41(October 17, 2000)
- ISSN：1520-4995
文摘
Murine class alpha glutathione S-transferase A1-1 (mGSTA1-1), unlike mammalian class alphaGSTs, is the most efficient in the glutathione (GSH) conjugation of the ultimate carcinogenic metaboliteof benzo[a]pyrene, (+)-anti-7,8-dihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE][Hu, X., Srivastava, S. K., Xia, H., Awasthi, Y. C., and Singh, S. V. (1996) J. Biol. Chem. 271, 32684-32688]. Here, we report the crystal structures of mGSTA1-1 in complex with GSH and with the GSHconjugate of (+)-anti-BPDE (GSBpd) at 1.9 and 2.0 Å resolution, respectively. Both crystals belong tomonoclinic space group C2 with one dimer in the asymmetric unit. The structures reveal that, within onesubunit, the GSH moiety interacts with residues Y8, R14, K44, Q53, V54, Q66, and T67, whereas thehydrophobic moiety of GSBpd interacts with the side chains of F9, R14, M207, A215, R216, F219, andI221. In addition, the GSH moiety interacts with D100 and R130 from the other subunit across the dimerinterface. The structural comparison between mGSTA1-1·GSH and mGSTA1-1·GSBpd reveals significantconformational differences. The movement of helix 
9 brings the residues on the helix into direct interactionwith the product. Most noticeable are the positional displacement and conformational change of R216,one of the residues located in helix 9. The side chain of R216, which points away from the H-site in themGSTA1-1·GSH complex, probes into the active site and becomes parallel with the aromatic ring systemof GSBpd. Moreover, the guanidinium group of R216 shifts ~8 Å and forms a strong hydrogen bondwith the C8 hydroxyl group of GSBpd, suggesting that the electrostatic assistance provided by theguanidinium group facilitates the ring-opening reaction of (+)-anti-BPDE. The structure of mGSTA1-1·GSBpd is also compared with those of hGSTP1-1[V104,A113]·GSBpd, hGSPA1-1·S-benzylglutathione,and mGSTA4-4·4-S-glutathionyl-5-pentyltetrahydrofuran-2-ol. The comparison provides further evidencethat supports the functional roles of R216 and helix 9. The lack of mobility of helix 9 and/or the lackof electrostatic assistance from R216 may be responsible for the relatively lower activity of hGSTA1-1,mGSTA4-4, and hGSTP1-1 toward (+)-anti-BPDE.
9 brings the residues on the helix into direct interactionwith the product. Most noticeable are the positional displacement and conformational change of R216,one of the residues located in helix 9. The side chain of R216, which points away from the H-site in themGSTA1-1·GSH complex, probes into the active site and becomes parallel with the aromatic ring systemof GSBpd. Moreover, the guanidinium group of R216 shifts ~8 Å and forms a strong hydrogen bondwith the C8 hydroxyl group of GSBpd, suggesting that the electrostatic assistance provided by theguanidinium group facilitates the ring-opening reaction of (+)-anti-BPDE. The structure of mGSTA1-1·GSBpd is also compared with those of hGSTP1-1[V104,A113]·GSBpd, hGSPA1-1·S-benzylglutathione,and mGSTA4-4·4-S-glutathionyl-5-pentyltetrahydrofuran-2-ol. The comparison provides further evidencethat supports the functional roles of R216 and helix 9. The lack of mobility of helix 9 and/or the lackof electrostatic assistance from R216 may be responsible for the relatively lower activity of hGSTA1-1,mGSTA4-4, and hGSTP1-1 toward (+)-anti-BPDE.