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Lysozyme (EC 3.2.1.17, muramidase, N-acetylmuramide glycanhydrolase; systematic name peptidoglycan N-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside hydrolase that catalyzes the following process:
The peptidoglycan layer within the bacterial cell wall is a crystal lattice structure formed from linear chains of two alternating amino sugars, namely N-acetylglucosamine (GlcNAc or NAG) and N-acetylmuramic acid (MurNAc or NAM). The alternating sugars are connected by a β-(1,4)-glycosidic bond.
The enzyme hydrolyses the 1,4-beta linkages between N-acetyl-D-glucosamine and N-acetylmuramic acid in peptidoglycan heteropolymers of prokaryotic cell walls. E. coli endolysin also functions in bacterial cell lysis and acts as a transglycosylase. The T4 lysozyme structure contains 2 domains, the interface between which forms the active-site cleft.
The basic components are N-acetylglucosamine and N-acetyltalosaminuronic acid (bacterial peptidoglycan containing N-acetylmuramic acid instead), which are linked by β-1,3-glycosidic bonds. [3] Lysozyme, a host defense mechanism present in human secretions (e.g. saliva and tears) breaks β-1,4-glycosidic bonds to degrade peptidoglycan. However ...
The chemical structure of the outer membrane's lipopolysaccharide is often unique to specific bacterial sub-species and is responsible for many of the antigenic properties of these strains. In addition to the peptidoglycan layer the Gram-negative cell wall also contains an additional outer membrane composed of phospholipids and ...
Peptidoglycan binding domains have a general peptidoglycan binding function and a common core structure consisting of a closed, three-helical bundle with a left-handed twist. It is found at the N or C terminus of a variety of enzymes involved in bacterial cell wall degradation.
Organisation of enzyme structure and lysozyme example. Binding sites in blue, catalytic site in red and peptidoglycan substrate in black. (In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction.
The lysin catalytic domain digests peptidoglycan locally at a high rate, which causes holes in the cell wall. Since the cross-linked peptidoglycan cell wall is the only mechanism that prevents the spontaneous burst of bacterial cells due to the high internal pressure (3 to 5 atmospheres), enzymatic digestion by lysins irreversibly causes ...