Proton nuclear magnetic resonance study of an active pentapeptide fragment of ubiquitin

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Abstract
The aqueous solution conformation of Tyr-Asn-Ile-Gln-Lys (UB5) corresponding to positions 59-63 of the polypeptide, ubiquitin, was investigated by proton NMR. Like the parent protein, UB5 induces nonspecifically both T and B lymphocyte differentiation. The various NH and CH resonances of this pentapeptide were assigned, and its solution conformation was probed through a study of chemical shift variations with pH, temperature dependence of amide hydrogen chemical shifts, vicinal NH-C.alpha.H and C.alpha.H-C.beta.H2 coupling constant data and amide hydrogen-exchange rates. The latter were measured in H2O by using a combination of transfer of solvent saturation and saturation recovery NMR experiments. The data are compatible with the assumption of a highly motile dynamic equilibrium among different conformations for this peptide. The various secondary amide hydrogens remain essentially exposed to the solvent. The temperature-dependence study of the amide hydrogen chemical shifts also did not reveal any strong internal hydrogen bonds. A rotamer population analysis of Tyr and Asn side chains suggests that 2 of the rotomers are predominantly populated for each of these residues. The dynamic conformation of UB5 in aqueous solution is described.

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