The lubricant of life: a proposal that solvent water promotes extremely fast conformational fluctuations in mobile heteropolypeptide structure.

Recent observations using the novel technique of Raman optical activity suggest that individual residues in unfolded proteins and in disordered loop regions of molten globule-like states cluster in the alpha-helix, beta-structure, and PPII-helix regions of the Ramachandran surface and that they "flicker" between these regions at rates approximately 10(12) s-1 at room temperature. It is proposed that these rapid motions, which occur on the same picosecond time scale as rearrangements of the hydrogen bond network in bulk water, are promoted by solvent water molecules via a repertoire of transient hydrated reverse turn conformations. Some implications of this proposal for protein folding and function are discussed.