Endo-beta-N-acetylglucosaminidase:Possible Functions and Mechanisms
Endo-beta-N-acetylglucosaminidase(ENGase)is widely distributed in various organisms.The first reported ENGase activity was detected in Diplococcus pneumoniae in 1971.The protein(Endo D)was purified and its peptide sequence was determined in 1974.Three ENGases(Endo F1-F3)were discovered in Flavobacterium meningosepticum from 1982 to 1993.After that,the activity was detected from different species of bacteria,yeast,fungal,plant,mice,human,etc.Multiple ENGases were detected in some species,such as Arabidopsis thaliana and Trichoderma atroviride.The first preliminary crystallographic analysis of ENGase was conducted in 1994.But to date,only a few ENGases structures have been obtained,and the structure of human ENGase is still missing.The currently identified ENGases were distributed in the GH18 or GH85 families in Carbohydrate-Active enZyme(CAZy)database.GH18 ENGase only has hydrolytic activity,but GH85 ENGase has both hydrolytic and transglycosylation activity.Although ENGases of the two families have similar(β/α)8-TIM barrel structures,the active sites are slightly different.ENGase is an effective tool for glycan detection and glycan editing.Biochemically,ENGase can specifically hydrolyze β-1,4 glycosidic bond between the two N-acetylglucosamines(GlcNAc)on core pentasaccharide presented on glycopeptides and/or glycoproteins.Different ENGases may have different substrate specificity.The hydrolysis products are oligosaccharide chains and a GlcNAc or glycopeptides or glycoproteins with a GlcNAc.Conditionally,it can use the two products to produce a new glycopeptides or glycoprotein.Although ENGase is a common presentation in cell,its biological function remains unclear.Accumulated evidences demonstrated that ENGase is a none essential gene for living and a key regulator for differentiation.No ENGase gene was detected in the genomes of Saccharomyces cerevisiae and three other yeast species.Its expression was extremely low in lung.As glycoproteins are not produced by prokaryotic cells,a role for nutrition and/or microbial-host interaction was predicted for bacterium produced enzymes.In the embryonic lethality phenotype of the Nglyl-deficient mice can be partially rescued by Engase knockout,suggesting down regulation of Engase might be a solution for stress induced adaptation.Potential impacts of ENGase regulation on health and disease were presented.Rabeprazole,a drug used for stomach pain as a proton inhibitor,was identified as an inhibitor for ENGase.ENGases have been applied in vitro to produce antibodies with a designated glycan.The two step reactions were achieved by a pair of ENGase dominated for hydrolysis of substrate glycoprotein and synthesis of new glycoprotein with a free glycan of designed structure,respectively.In addition,ENGase was also been used in cell surface glycan editing.New application scenarios and new detection methods for glycobiological engineering are quickly opened up by the two functions of ENGase,especially in antibody remodeling and antibody drug conjugates.The discovery,distribution,structure property,enzymatic characteristics and recent researches in topical model organisms of ENGase were reviewed in this paper.Possible biological functions and mechanisms of ENGase,including differentiation,digestion of glycoproteins for nutrition and stress responding were hypothesised.In addition,the role of ENGase in glycan editing and synthetic biology was discussed.We hope this paper may provide insights for ENGase research and lay a solid foundation for applied and translational glycomics.
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