Contributed by Narine Arabyan
Lysozyme hydrolyzes the β-1,4-glycosidic bond of oligosaccharides. These enzymes are part of a broad group of glycosyl hydrolases that are poorly characterized. Lysozyme enzymes belong to the GH24 family of glycosyl hydrolases (GHs)1. GHs play an important role during infection by altering the host glycan structure to gain access of the host epithelial cells by binding to terminal monosaccharides to initiate glycan degradation2. Lysozyme enzymes may be new promising virulence factors due to its β-1,4-glycosidase activity and have the potential to recognize host GlcNAc containing glycans in the form of N-glycans, O-glycans, glycolipids, glycoproteins and glucosaminoglycans during infection3. These GlcNAc molecules are linked to monosaccharides in the glycan via a β-1,4-glycosidic bond4 that can be cleaved by enzymes from Salmonella with lysozyme activity during host association.
Lysozyme enzymes with β-1,4-glycosidase activity are also involved during the secretion of proteins which is central for the virulence of all pathogenic bacteria1. Gram-negative organisms translocate proteins across the peptidoglycan that is composed of linear chains of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) and the alternating sugars are connected by β-1,4-glycosidic bonds5-7. The peptidoglycan structure is a physical barrier for the assembly of macromolecular complexes and for the transport of proteins. For this reason, all bacterial lysozymes degrade the peptidoglycan to allow the assembly of type III or type IV secretion systems essential in virulence, flagella, or conjugation8,9. This remodeling creates gaps in the peptidoglycan necessary for the assembly of these macromolecular systems. Intracellular pathogenic bacteria, such as Brucella abortus, use lysozyme during its early stages of intracellular replication8. Lysozyme enzymes are important for growth and are being recognized as emerging virulence factors.
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2 Arabyan, N. et al. Salmonella Degrades the Host Glycocalyx Leading to Altered Infection and Glycan Remodeling. Sci Rep 6, 29525, doi:10.1038/srep29525 (2016).
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9 Koraimann, G. Lytic transglycosylases in macromolecular transport systems of Gram-negative bacteria. Cell Mol Life Sci 60, 2371-2388, doi:10.1007/s00018-003-3056-1 (2003).
