Quasi-native transition and self-diffusion of proteins in water-glycerol mixture.

An orderly investigation of the levels of secondary and tertiary structures, kinetics of tertiary structural changes, and self diffusion coefficient of lysozyme and cytochrome c in the 0-70% (weight/volume) range of glycerol is reported. While secondary structural propensity of both proteins is larger in glycerol, results for tertiary structure and translational diffusion coefficient with increasing glycerol provide two contrasting depictions - lysozyme becomes increasingly compact, plausibly due to disulfide bridge constraints, but cytochrome c expands and loses the tertiary structure. The chain expansion and contraction corresponding to loss and reformation of tertiary structure of cytochrome c are ultrafast that occur in the submillisecond bin. Changes in protein conformation appear in as little as 2% glycerol, and the results suggest that glycerol does not unfold the protein but reversibly destabilizes to quasi-native state(s). These observations make one ponder whether results of studies on protein dynamics, relaxation, and conformational substates reported in literature can be associated with native-state properties.