| Lysozyme (muramidase), a ubiquitous glycoside hydrolase family 22 enzyme secreted across mucosal surfaces, granules, and exocrine glands, executes non-lytic bactericidal activity by catalyzing hydrolysis of β-1,4 glycosidic linkages between N-acetylmuramic acid and N-acetylglucosamine in Gram-positive peptidoglycan, creating protoplasts vulnerable to osmotic lysis. Its canonical α/α barrel fold cradles two glutamates and aspartates in the active site cleft, where Glu35 acts as general acid to protonate the scissile oxygen while Asp52 stabilizes the oxocarbenium ion intermediate, with rigid substrate positioning achieved through extensive hydrogen bonding to acetamido groups. Beyond canonical hydrolysis, lysozyme synergizes with lactoferrin-mediated iron sequestration and defensin pore formation to dismantle Gram-negative outer membranes through synergistic peptidoglycan exposure, while contributing to biofilm disruption via matrix polysaccharide degradation in chronic infections. Secreted by Paneth cells, neutrophils, and acinar cells under NF-κB and STAT3 transcriptional control during bacterial challenge, lysozyme maintains sterile barriers at gut, respiratory, and ocular surfaces, with constitutive tears/saliva levels providing immediate pathogen surveillance. Researchers exploit its heat stability and chromogenic substrate assays for real-time innate immune monitoring in organoid infection models or quantifying granulocyte degranulation via ELISA. Elevated serum levels serve as sarcoidosis activity biomarkers due to macrophage hypersecretion, while amyloidogenic mutations trigger hereditary renal amyloidosis through fibril deposition. |
Lane 1: RAW 264.7, Lane 2: THP-1
