NMR EVIDENCE FOR SLOW COLLECTIVE MOTIONS IN CYANOMETMYOGLOBIN

Residual dipolar couplings observed in NMR spectra at very high magnet ic fields have been measured to a high degree of accuracy for the para magnetic protein cyanometmyoglobin. Deviations of these measurements f rom predictions based on available crystallographic and solution struc tures are largely systematic and well correlated within a given helix of this highly alpha-helical protein. These observations can be explai ned by invoking collective motion and small displacements of represent ative helices from their reported average positions in the solid state , Thus, the measurements appear to be capable of providing important i nsights into slower, collective protein motions, which are likely to b e important for function, and which have been difficult to study using established experimental techniques.