The three-dimensional structure of mouse lysozyme M, glycoside hydrolase, with 130 amino acids has been determined by heteronuclear NMR spectroscopy. We found that mouse lysozyme M had four α-helices, two 310 helices, and a double- and a triple-stranded anti-parallel β-sheet, and its structure was very similar to that of hen lysozyme in solution and in the crystalline state. The pH activity profile of p-nitrophenyl penta N-acetyl-β-D-chitopentaoside hydrolysis by mouse lysozyme M was similar to that of hen lysozyme, but the hydrolytic activity of mouse lysozyme M was lower. From analyses of binding affinities of lysozymes to a substrate analogue and internal motions of lysozymes, we suggest that the lower activity of mouse lysozyme M was due to the larger dissociation constant of its enzyme-substrate complex and the restricted internal backbone motions in the molecule.
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