Study of partially folded states of cytochrome C by solvation dynamics

Solvation dynamics in the two partially folded states (IS′ and IS″) of a protein, cytochrome C′ has been studied using picosecond time resolved fluorescence spectroscopy. For IS′, 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, IS″, formed by the addition of 5 M urea to IS′, 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 IS″ may be attributed to the expanded and less compact structure of IS″ compared to IS′. The slower hydration dynamics in both IS′ and IS″, 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.