Lysozyme
The lysozyme is a globular Protéine of 129 Amino-acid that one meets in a certain number of secretions (Larme S, Salive…) and in the Egg white . She was discovered by Alexander Fleming in 1922.
It is about a acid Hydrolase (EC. 3.2.1.17) secreted by the Granulocyte S and the Monocyte S. She destroys the bacterial Paroi by catalyzing the Hydrolyze Glycosaminoglycanne S constituting it. This property encouraged certain authors to qualify it body Antibiotique.
Mode of action
The lysozyme can act like a innate Opsonine, or like a lytic enzyme able to lyse bacteria, in particular those in positive Gram, independently them pathogenic capacity. On the other hand, the bacteria with negative Gram are generally resistant to this enzyme thanks to the external layer of lipopolysaccharides (LPS) which characterizes them. This layer LPS covers the mureic wall (i.e., layer of peptidoglycannes) and protects it from the attack by the lysozyme by preventing the access from this enzyme.The lysozyme is used as innate nonspecific opsonin while being fixed at bacterial surface, thus reducing the negative charge and facilitating to the Phagocytose bacterium before opsonins of the acquired system of the immunity. In other words, the lysozyme facilitates phagocytosis by the Leucocytes.
Concerning, bacterial lysis, the enzyme attacks the peptidoglycannes constituting the wall of the Bacteria (particularly the Bacteria positive Gram. Indeed, the lysozyme hydrolize the covalent bonds between the muramic Acide N-acétyl with the 4th carbon atom of the N-acétyl glucosamine. The molecule of peptidoglycanne is associated with the site with fixing with the enzyme (binding site) located in a hollow between the two fields. That constrained the molecule of substrate to adopt the conformation of the state of transition. The Amino-acid Lime 35 (Glutamic acid, amino-acid number 35), and the Asp 52 (Aspartic acid, amino-acid number 52) proved to be essential to the enzymatic activity. Lime 35 acts like donor of Proton to the bridge glycosidic, cleaving the connection CO of the substrate, while Asp 52 is used as Nucléophile allowing the transitory formation of a glycosylée enzyme. This one reacts then with a molecule of Eau, giving the finished product of the hydrolysis and the enzyme in its initial form.
Diseases related to the lysozyme
A change on the Gène of the lysozyme can be at the origin of the accumulation of starch Protéines in certain fabrics.
Diagnostic use
An increased rate of lysozyme in blood is often related to a Sarcoïdose. Value of 8 mg/l or more is regarded as high.
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