Effects of glycosylation on protein conformation and amide proton exchange rates in RNase B

Assignment of most of the proton NMR resonances of bovine pancreatic RNase B has been achieved using standard NMR techniques and by comparison with the published assignments for RNase A. A comparison of the NMR spectra of RNase B with RNase A shows that glycosylation of the enzyme has little overall effect on the conformation of the protein in solution. Comparisons of hydrogen-deuterium solvent exchange rates for the NH protons of RNase A and RNase B were made using two-dimensional 1H correlation spectroscopy. In the case of the glycosylated enzyme the exchange rates decreased for the NH protons of residues 9-14, 23-24, 32, 34-35, 39-40, 43-44, 48-49, 60, 71, 75-76, 80, 83-85, 100-101, 107, 111 and 122, relative to the unglycosylated RNase A. These results are consistent with the presence of the oligosaccharide inducing enhanced global dynamic stability and consequent changes to the unfolding equilibrium of the enzyme. The enhanced stability is observed not only for residues in the vicinity of the glycosylation site, asparagine-34, but also at residues remote from this site, as much as 30 A away.