lysozyme

Lysozyme is a small enzyme that cleaves the polysaccharide component of bacterial cell walls, catalyzing hydrolysis of the β-1,4 glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid in peptidoglycan. It is a cationic antimicrobial protein found in many animal secretions, including tears, saliva, mucus, milk, and notably egg white, where it contributes to innate immunity. The most studied form is hen egg white lysozyme (HEWL), a 14.3 kDa protein of 129 amino acids that contains four disulfide bonds. Its active site is a deep cleft with two catalytic residues, Glu35 and Asp52, which promote bond cleavage through an acid-base mechanism.

Lysozyme is effective mainly against Gram-positive bacteria, whose thick peptidoglycan layer is accessible to the enzyme; Gram-negative bacteria are more resistant due to their outer membrane. In addition to its antimicrobial function, lysozyme serves as a widely used model enzyme in biochemistry and structural biology for studying protein folding, stability, and enzyme catalysis.

Historically, lysozyme was discovered by Alexander Fleming in 1922 and subsequently purified and characterized, becoming one of the first enzymes to be studied in detail. Beyond natural secretions, lysozyme is produced industrially for research use and employed as a preservative in some foods and beverages to limit bacterial growth.