Nuclear magnetic resonance study of a hybrid of bovine and rat ribonuclease.

A hybrid RNase S', consisting of synthetic S-peptide of rat ribonuclease and bovine S-protein, was studied by 1H n.m.r. to determine the effects of the many N-terminal amino acid replacements in rat S-peptide as compared to bovine S-peptide. As judged from the aromatic resonances, the conformation of the hybrid RNase S' is essentially identical to the conformation of bovine RNase S'. Notably, the active-site histidines 12 and 119 were not affected by the substitutions in the S-peptide, confirming earlier findings that the catalytic properties of naturally occurring RNases are modulated by the S-protein part of the molecule only. However, the resonances of Tyr-25 and His-48, which in RNase A are involved in a pH-dependent conformational transition, appeared to be different in the hybrid RNase, demonstrating that amino acid replacements may influence the structure of the protein locally.