Study of partially folded states of cytochrome C by solvation dynamics

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. (C) 2005 Elsevier B.V. All rights reserved.