Correlation between sites of limited proteolysis and segmental mobility in thermolysin

Limited proteolysis or autolysis of thermolysin under different experimental conditions leads to fission of a small number of peptide bonds located in exposed surface segments of the polypeptide chain characterized by highest mobility, as given by the temperature factors (B values) determined crystallographically [Holmes, M.A., & Matthews, B.W. (1982) J. Mol. Biol. 160, 623-639]. Considering also similar findings observed previously with other protein systems, it is proposed that this correlation between segmental mobility and sites of limited proteolysis in globular proteins is quite general. Thus, flexibility of the polypeptide chain of a globular protein at the site of proteolytic attack promotes optimal binding and proper interaction with the active site of the protease. These findings emphasize that apparent thermal motion seen in protein crystals is relevant to motion in solution and appear to be of general significance in protein-protein recognition processes.