Class Pi Glutathione Transferase Unfolds via a Dimeric and Not Monomeric Intermediate: Functional Implications for an Unstable Monomer
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- 作者：Samantha Gildenhuys ; Louise A. Wallace ; Jonathan P. Burke ; David Balchin ; Yasien Sayed ; Heini W. Dirr
- 刊名：Biochemistry
- 出版年：2010
- 出版时间：June 22, 2010
- 年：2010
- 卷：49
- 期：24
- 页码：5074-5081
- 全文大小：832K
- 年卷期：v.49,no.24(June 22, 2010)
- ISSN：1520-4995
文摘
Cytosolic class pi glutathione transferase P1-1 (GSTP1-1) is associated with drug resistance and proliferative pathways because of its catalytic detoxification properties and ability to bind and regulate protein kinases. The native wild-type protein is homodimeric, and whereas the dimeric structure is required for catalytic functionality, a monomeric and not dimeric form of class pi GST is reported to mediate its interaction with and inhibit the activity of the pro-apoptotic enzyme c-Jun N-terminal kinase (JNK) [Adler, V., et al. (1999) EMBO J. 18, 1321−1334]. Thus, the existence of a stable monomeric form of wild-type class pi GST appears to have physiological relevance. However, there are conflicting accounts of the subunit’s intrinsic stability since it has been reported to be either unstable [Dirr, H., and Reinemer, P. (1991) Biochem. Biophys. Res. Commun. 180, 294−300] or stable [Aceto, A., et al. (1992) Biochem. J. 285, 241−245]. In this study, the conformational stability of GSTP1-1 was re-examined by equilibrium folding and unfolding kinetics experiments. The data do not demonstrate the existence of a stable monomer but that unfolding of hGSTP1-1 proceeds via an inactive, nativelike dimeric intermediate in which the highly dynamic helix 2 is unfolded. Furthermore, molecular modeling results indicate that a dimeric GSTP1-1 can bind JNK. According to the available evidence with regard to the stability of the monomeric and dimeric forms of GSTP1-1 and the modality of the GST−JNK interaction, formation of a complex between GSTP1-1 and JNK most likely involves the dimeric form of the GST and not its monomer as is commonly reported.