Protein folding from heterogeneous unfolded state revealed by time-resolved X-ray solution scattering
Tae Wu Kim, Sang Jin Lee, Junbeom Jo, Jong Goo Kim, Hosung Ki, Chang Woo Kim, Kwang Hyun Cho, Jungkweon Choi, Jae Hyuk Lee, Michaël Wulff, Young Min Rhee, Hyotcherl Ihee
Abstract
(cyt-c) induced by external electron injection by using time-resolved X-ray solution scattering. A systematic kinetic analysis unveils a kinetic model for its folding with a stretched exponential behavior during the transition toward the folded state. With the aid of the ensemble optimization method combined with molecular dynamics simulations, we found that during the folding the heterogeneously populated ensemble of the unfolded state is converted to a narrowly populated ensemble of folded conformations. These observations obtained from the kinetic and the structural analyses of X-ray scattering data reveal that the folding dynamics of cyt-c accompanies many parallel pathways associated with the heterogeneously populated ensemble of unfolded conformations, resulting in the stretched exponential kinetics at room temperature. This finding provides direct evidence with a view to microscopic protein conformations that the cyt-c folding initiates from a highly heterogeneous unfolded state, passes through still diverse intermediate structures, and reaches structural homogeneity by arriving at the folded state.