Molecular and structural biostudies on streptococcalinyasion/infection mechanisms to host cells through degradation of extracellular matrices glyoceaminoglycans

点击翻译按钮获取中文摘要

Some pathogenic microorganisms produce polysaccharide-degrading enzymes (lyases and hydrolases) to invade mammalian and/or plant cells. Mammalian glycosaminoglycans that form part of cell surface matrix are typical targets for microbial enzymes. Unsaturated glucuronyl hydrolase (UGL), which was genetically first identified in Bacillus sp. strain GL1, catalyzes the hydrolytic release of an unsaturated uronic acid from oligosaccharides produced through the reaction of the matrix-degrading polysaccharide lyases (e.g., hyaluronate and chondroitin lyases), suggesting that these enzymes function as a virulent factor in microbial infection. In this study, structure and function relationship of glycosaminoglycan-degrading enzymes, lyase and hydrolase, was analyzed.Based on X-ray crystallography of enzyme-substrate complexes and site-directed mutagenesis, mechanisms for catalytic reaction and substrate recognition of hyaluronate lyase homologue (xanthan lyase) were clarified. A single tyrosine … More residue abstracts C5-proton of the uronate residue at subsite +1 and donates the proton to glycosidic bond to be cleaved.In contrast with general glycoside hydrolases with the retention or inversion catalytic mechanism of an anomeric configuration, UGL uniquely triggers hydrolysis of vinyl ether groups in the unsaturated uronate residue but not of the glycosidic bond.Recent complete genome sequence analyses indicate that a large number of microorganisms ranging from bacteria to fungi (over 70 species) have a UGL homologous gene in their genome. In the Carbohydrate-Active enZyme (CAZy) database, UGL and its homologues form a new family, GH-88. Microbial producers of UGL include pathogenic bacteria such as clostridia, streptococci, and vibrios. The enzyme homologous gene has been found especially in streptococci, Streptococcus agalactiae, Streptococcus pneumoniae, Streptococcus pyogenes, and Streptococcus suis. Unlike the bacillus UGL, streptococcal UGL acts on unsaturated chondroitin disaccharide with a sulfate group at C4 of GalNAc. Less