Lysozyme

Lysozyme is an enzyme that hydrolyzes bonds in peptidoglycan and related bacterial cell-wall polysaccharides. It helps damage bacterial cell walls and occurs in animal secretions and other biological settings.

Peptidoglycan: A mesh-like polymer of sugars and short peptides that forms the structural framework of most bacterial cell walls. It is the principal bacterial-wall substrate whose glycan backbone lysozyme cleaves.
Innate immune system: The rapid, broadly targeted defenses that detect and limit infection without requiring prior exposure to a pathogen. Lysozyme is one of the soluble antimicrobial defenses operating within innate immunity.
Alexander Fleming: A Scottish physician and microbiologist who discovered lysozyme and later penicillin. Fleming reported lysozyme in 1922 after observing antibacterial activity in nasal mucus.
β-Lactam antibiotics: Antibiotics that inhibit bacterial cell-wall cross-linking by binding penicillin-binding proteins. They prevent peptidoglycan assembly rather than enzymatically cutting existing sugar chains.
Glycoside hydrolase: An enzyme that hydrolyzes glycosidic bonds linking sugars or sugar-derived molecules. Lysozyme belongs to this enzyme family because it cleaves a sugar-chain bond using water.
Tear film: The thin fluid layer covering the eye’s exposed surface, containing water, salts, proteins, and antimicrobial molecules. Tears deliver lysozyme to the eye surface, where it contributes to antimicrobial protection.
Penicillin: A group of β-lactam antibiotics that inhibit bacterial cell-wall synthesis by targeting penicillin-binding proteins. Fleming’s later antibiotic discovery targets wall construction, unlike lysozyme’s direct cleavage of wall polysaccharides.
Bacteriophage endolysin: A phage-produced enzyme that breaks bacterial cell-wall components to release newly formed virus particles. Endolysins serve a similar wall-rupturing function but are produced by bacteriophages and include diverse enzyme types.
Glycosidic bond: A covalent bond joining a carbohydrate’s anomeric carbon to another group, including another sugar. Lysozyme hydrolyzes the bond connecting alternating sugars in peptidoglycan.
Human milk: The milk produced by humans, containing nutrients and bioactive molecules that support infant development and defense. Lysozyme is abundant in human milk and contributes to its antimicrobial properties.

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