Lysozyme requires fluctuation of the active site for the manifestation of activity

Mutations around His15 which lie far away from the active site, stimulated glycol chitin activity of lysozyme at physiological temperature. Del-Argl4Hisl5 lysozyme, a mutant lysozyme whose Argl4 and Hisl5 were deleted together, and has the highest activity among these mutant lysozymes, had a similar binding ability to a trimer of N-acetyl-glucosamine, a substrate analogue, relative to native lysozyme. This suggests that the increased activity was due to an increased k_cat in the catalysis reaction. The H-D exchange rate of the N-1 proton in the Trp63 which is located in the active site cleft, was enhanced in the Del-Argl4Hisl5 lysozyme, while 2-D proton NMR analysis revealed no conformational change around Trp63. We conclude that some sort of fluctuation at the active site might be required for the manifestation of activity. This theory is supported by the finding that the Del-Argl4Hisl5 lysozyme showed a shift in temperature dependency of activity to lower temperatures compared with that of native lysozyme.