Vibrational normal-mode spectrum of globular proteins

Slow vibrational modes of proteins (in the 5-psec range) have been the focus of numerous recent studies. Nevertheless, no attempt has yet been made to ascertain the general properties of these vibrational spectra. Comparing the spectra of several globular proteins, it is found that the density of states follows a characteristic, universal curve, which reflects the main structural similarities between proteins. The spectral (or fracton) dimension is ${\mathit{d}}_{\mathit{s}}$=2: for the slower modes, the density of states increases linearly with the frequency, as opposed to the regular increase with the square of the frequency, as in crystals. This is relevant to the kinetics of the mechanical transport of signals in proteins and to the function of proteins as catalysts.