DIFFERENCES IN CONFORMATIONAL DYNAMICS OF RIBONUCLEASE-A AND RIBONUCLEASE-S AS OBSERVED BY INFRARED-SPECTROSCOPY AND HYDROGEN-DEUTERIUM EXCHANGE

Differences in conformational dynamics of bovine pancreatic RNase A an d RNase S have been investigated using hydrogen-deuterium (H-D) exchan ge in conjunction with Fourier transform infrared spectroscopy, Deuter ation-induced spectral changes in the amide I and II regions were moni tored as a function of time. Second-derivative analysis revealed simil ar amide I spectral patterns for both proteins in H2O as well as fully deuterated in D2O. However, the rate of amide proton exchange of RNas e S is much faster than that of RNase A at 25 degrees C as determined by changes in the intensity ratio of amide II/amide I bands and freque ncy red-shifts of amide I components. The frequency red-shifts of the amide I components ascribed to beta-sheet, alpha-helix, and beta-turns are continuous as a function of time, indicating that both proteins a re too small to contain isolated secondary structural groups containin g only exchanged or unexchanged amide protons in the partially deutera ted intermediate states. Despite the dramatic difference in H-D exchan ge rate, the patterns of spectral changes in the conformation-sensitiv e amide I regions of RNase A and RNase S are very similar throughout t he course of deuteration, indicating a similar pathway of amide proton exchange in both proteins. (C) 1996 Academic Press, Inc.