Approximate values for force constant and wave number associated with a low-frequency concerted motion in proteins can be evaluated by a comparison of X-ray structures

An approximate value for the force constant and the wave number of the low-frequency [beta]-sheet breathing motion of RNase A was calculated by employing the Boltzmann hypothesis on a set of data derived from a simple conventional structural superimposition of an unusual large number of X-ray structures available for the protein. The calculated value for the force constant associated with the breathing motion of RNase A is comparable to that describing the hinge-bending motion between the A-B and C-D dimers in the tetrameric structure of human S-adenosylhomocysteine hydrolase and the value determined for lysozyme hinge bending.