PNNL

Abstract

With the goal of investigating dynamical features of hydrophobic cores of proteins over a wide range of temperatures, the villin headpiece subdomain protein (HP36) was labeled at a "single" site corresponding to any one of the two -C5D3 groups of Leucine-69, which is located in a key position of the core. The main techniques employed are deuteron NMR quadrupolar echo line shape analysis, and T1Z (Zeeman) and T1Q (Quadrupolar order) relaxation experiments performed at 11.7 and 17.6T over the temperature range of 112 to 298K. The experimental data are compared with computer simulations. The deuteron line shapes give an excellent fit to a three-mode motional model that consists of a) fast 3-site rotational jumps about the pseudo C3 methyl spinning axis, b) slower reorientation of the spinning axis, described by diffusion along a restricted arc and c) large angle jumps between traces of rotameric conformers. Relaxation behavior is described by a phenomenological distribution of activation energies for 3-site hops at high temperatures that collapses to a single, distinctly smaller value for lower temperatures.