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[Audio] LYSOZYME Nature's Own Antibacterial Enzyme Structure · Mechanism · Sources · Applications 1 / 8.

[Audio] What Is Lysozyme? A small, robust enzyme (~14.3 kDa, 129 amino acids) that destroys bacterial cell walls. First identified as “muramidase” for its target: the peptidoglycan layer of bacterial walls. Acts as part of the innate immune system — a first line of chemical defense against microbes. One of the most-studied enzymes in biochemistry; a model system for enzyme kinetics research. 14.3 kDa Molecular weight Amino acid residues Year of discovery Antibacterial Enzyme Well-studied OVERVIEW 2 / 8.

[Audio] A Serendipitous Discovery Today A cold, and a clue Naming the enzyme Structure solved A model enzyme Alexander Fleming, nursing a cold, let a drop of his own nasal mucus fall onto a bacterial culture plate — and noticed the bacteria nearby dissolved. Fleming identified the active substance in tears, saliva, and mucus, naming it “lysozyme” for its ability to lyse (dissolve) bacterial cells. David Chilton Phillips determined lysozyme's 3D structure by X-ray crystallography — the first enzyme structure ever solved. Lysozyme remains a textbook model for studying enzyme structure, catalysis, and protein folding. 3 / 8.

[Audio] Structure of Lysozyme Key Catalytic Residues Glu35 Acts as a general acid — donates a proton to break the glycosidic bond. Asp52 Compact globular protein with a deep active-site cleft Stabilizes the positively charged reaction intermediate as a nucleophile/general base. Two lobes form a cleft between them — the substrate-binding groove Trp62 & Trp63 Line the binding cleft and help position the sugar substrate. 4 disulfide bonds lock the structure, giving it exceptional stability Mixed fold: alpha-helical domain + beta-sheet domain MOLECULAR ARCHITECTURE 4 / 8.

[Audio] How Lysozyme Kills Bacteria Target: the peptidoglycan layer of the bacterial cell wall Bind Strain Cleave Rupture The enzyme's cleft grips a chain of peptidoglycan, positioning two specific sugar units in the active site. Binding distorts the sugar ring into a strained, high-energy half-chair shape. Glu35 and Asp52 catalyze hydrolysis of the β-1,4 glycosidic bond between NAM and NAG sugars. The cell wall loses structural integrity; osmotic pressure bursts the bacterium. → → → 5 / 8.

[Audio] Where Is Lysozyme Found? Widely distributed across body fluids, tissues, and the natural world Human Secretions Egg White Immune Cells Across Species Tears, saliva, mucus, and human milk — mucosal surfaces exposed to microbes. Hen egg white is the richest natural source (~3.5% of total protein) and the standard for research and industrial extraction. Produced by neutrophils and macrophages, and released to fight invading bacteria. Found in many organisms — mammals, birds, insects, and even some plants and bacteriophages. NATURAL DISTRIBUTION 6 / 8.

[Audio] Applications of Lysozyme Medicine Food Preservation Used in eye drops, wound dressings, and as an anti-inflammatory / antimicrobial agent; studied for treating certain infections. A natural preservative (E1105) in cheese, wine, and processed meats — inhibits spoilage bacteria like Clostridium tyrobutyricum. Research Tool Biotechnology A benchmark protein for structural biology, enzyme kinetics, and protein-folding studies for over 60 years. Used to lyse bacterial cell walls in labs for DNA/protein extraction and to create protoplasts. 7 / 8.

[Audio] Key Takeaways A small, stable enzyme that cleaves bacterial peptidoglycan to destroy cell walls. Discovered by Alexander Fleming in 1922; the first enzyme whose structure was solved by X-ray crystallography. Naturally abundant in tears, saliva, egg white, and immune cells — a key part of innate immunity. Applied today in medicine, food preservation, and as a foundational model in biochemistry research. A tiny enzyme with an outsized role in natural defense. 8 / 8.