Pressure-induced local unfolding of the Ras binding domain of RalGDS

The reliable prediction of the precise three-dimensional structure of prote ins from their amino acid sequence is a major, still unresolved problem in biochemistry. Pressure is a parameter that controls folding/unfolding trans itions of proteins through the volume change Delta V of the protein-solvent system. By varying the pressure from 30 to 2,000 bar we detected using N-1 5/H-1 2D NMR spectroscopy a unique equilibrium unfolding intermediate I in the Ras binding domain of the Ral guanine nucleotide dissociation stimulato r (Ral GDS). It is characterized by a local melting of specific structural elements near hydrophobic cavities while the overall folded structure is ma intained.