The enzymology and cationicity of human lysozyme.

(A) The active site of lysozyme accommodates up to 6 consecutive sugars through 6 subsite contacts, annotated A-F. Lysozyme hydrolyzes the β-1,4 glycosidic bond between the NAM at subsite D and the NAG at subsite E [1]. (B) Ribbon model of human lysozyme highlighting the essential active site residues, an aspartic acid (blue) and a glutamic acid (orange). (C) Electrostatic potential map of human lysozyme (isoelectric point, 9.28). Because the bacterial envelope is negative, lysozyme may have an enhanced charge-mediated attraction for the bacterial surface that is proposed to lead to a catalytic-independent mechanism of bacterial killing. This structure was created using space-filling models in the PyMOL molecular graphics system. The electrostatic potential map was then calculated with the APBS Tools plug-in for PyMOL with default settings (contoured at ± 5kT/e; blue, positive; red, negative; white, hydrophobic). Human lysozyme, PDB accession 1REX. Abbreviations: NAG, N-acetylglucosamine; NAM, N-acetylmuramic acid; PDB, Protein Data Bank.