Molecular dynamics simulations of human glutathione transferase P1-1: Conformational fluctuations of the apo-structure

We have investigated by molecular dynamics simulations the conformational f luctuations of the monomer of human apo-glutathione transferase P1-1, After attainment of steady-state dynamics, the structural fluctuations involve m ainly the protein segments that participate also in the holo-apo transition discussed in the accompanying article (Stella et al,, 1999:37:1-9.). The m ost mobile region is the C-terminal segment of helix 2, In contrast, helice s 1, 6, 7, and 8 constitute a relatively rigid protein core, An "essential dynamics" analysis of the simulation shows that the largest fluctuations in volve specific regions of glutathione transferases. In such regions, atomic motions are correlated. Motions of helix 2 are accounted for by the second most prominent principal component, which reveals a fluctuation between tw o distinct conformations. The residues that constitute the II-site undergo a breathing motion, possibly relevant during the binding of hydrophobic cos ubstrates. Based on our simulation, several experimental findings can be ra tionalized, including the viscosity-dependent reactivity of Cys 47 and Cys 101 as well as the selective proteolysis of the peptide bond between Lys 44 and Ala 45, We have also modeled the structural changes that lead to the f ormation of an intrachain disulfide bridge between cysteines 47 and 101 and to the inactivation of the enzyme. The resulting structure maintains essen tially the native fold except for helix 2, which closes the G-site, (C) 199 9 Wiley-Liss, Inc.