HYDRATION OF THE PARTIALLY FOLDED PEPTIDE RN-24 STUDIED BY MULTIDIMENSIONAL NMR

Peptide-water interactions of a ribonuclease C-peptide analogue, RN-24 (Suc-AETAAAKFLRAHA-NH2) which exhibits significant helicity, have bee n studied in solution using homonuclear 2D and 3D NMR cross-relaxation experiments. Dipolar peptide proton-water proton interactions are ind icated by a large number of NOESY-type cross peaks at the H2O resonanc e frequency, most of them with opposite sign relative to the diagonal. Some cross peaks arise from intrapeptide cross relaxation to labile p rotons of histidine, threonine, lysine and arginine side chains. The o bserved peptide-water interactions are rather uniformly distributed, i nvolving peptide backbone and side chains equally. The data are consis tent with rapid fluctuations of the conformational ensemble and the ab sence of peptide regions that are highly shielded from bulk solvent, e ven in a peptide that exhibits high propensities for formation of heli cal secondary structure.