Wallace, Louise A, Blatch, Gregory ORCID: 0000-0003-0778-8577 and Dirr, Heini W (1998) A topologically conserved aliphatic residue in α-helix 6 stabilizes the hydrophobic core in domain II of glutathione transferases and is a structural determinant for the unfolding pathway. Biochemical Journal, 336 (2). pp. 413-418. ISSN 0264-6021

Abstract

A topologically conserved residue in a-helix 6 of domain II of human glutathione transferase (hGST) A1-1 was mutated to investigate its contribution to protein stability and the unfolding pathway. The replacement of Leu-164 with alanine (L164A) did not impact on the functional and gross structural properties of native hGST A1-1. The wild-type protein unfolds via a threestate pathway in which only folded dimer and unfolded monomer were highly populated at equilibrium; a native-like dimeric intermediate with partially dissociated domains I and II was detected using stopped-¯ow ¯uorescence studies [Wallace, Sluis- Cremer and Dirr (1998) Biochemistry 37, 5320±5328]. In the present study, urea-induced equilibrium unfolding of L164A hGST A1-1 indicated a destabilization of the native state and suggested the presence of a stable dimeric intermediate. The unfolding kinetic pathway for L164A hGST A1-1, like that for the wild type, is biphasic, with a fast and a slow unfolding event; the cavity-forming mutation has a substantially greater effect on the rate of unfolding of the fast event. The equilibrium and kinetic unfolding data for L164A hGST A1-1 suggest that a rapid pre-equilibrium is established between the native dimer and a dimeric intermediate before complete domain and subunit dissociation and unfolding. It is proposed that the topologically conserved bulky residue in a-helix 6 plays a role in specifying and stabilizing the core of domain II and the interface of domains I and II.

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