Study of partially folded states of cytochrome C by solvation dynamics

Abstract

Solvation dynamics in the two partially folded states (I_S' and I_S") of a protein, cytochrome C' has been studied using picosecond time resolved fluorescence spectroscopy. For I_S', formed by the addition of 2 mM sodium dodecyl sulfate (SDS) to the protein, almost total dynamic solvent shift of coumarin 153 (C153) is captured in a picosecond set up and two components of 90 and 400 ps are detected. In another partially unfolded state, I_S", formed by the addition of 5 M urea to I_S', only 22% of the total dynamic solvent shift is detected and there are two slow components of 60 and 170 ps. The faster dynamics in I_S" may be attributed to the expanded and less compact structure of I_S" compared to I_S'. The slower hydration dynamics in both I_S' and I_S", in comparison to bulk water (solvation time ≤ 1 ps), is ascribed to the local secondary structure, dynamics of the protein side chain and hindered exchange of bound and free water molecules in cytochrome C surrounded by SDS and urea.