Abstract
C. canimorsus 5 has the capacity to grow at the expenses of glycan moieties from host cells N-glycoproteins. Here, we show that C. canimorsus 5 also has the capacity to deglycosylate human IgG and we analyze the deglycosylation mechanism. We show that deglycosylation is achieved by a large complex spanning the outer membrane and consisting of the Gpd proteins and sialidase SiaC. GpdD, -G, -E and -F are surface-exposed outer membrane lipoproteins. GpdDEF could contribute to the binding of glycoproteins at the bacterial surface while GpdG is a endo-β-N-acetylglucosaminidase cleaving the N-linked oligosaccharide after the first N-linked GlcNAc residue. GpdC, resembling a TonB-dependent OM transporter is presumed to import the oligosaccharide into the periplasm after its cleavage from the glycoprotein. The terminal sialic acid residue of the oligosaccharide is then removed by SiaC, a periplasm-exposed lipoprotein in direct contact with GpdC. Finally, most likely degradation of the oligosaccharide proceeds sequentially from the desialylated non reducing end by the action of periplasmic exoglycosidases, including β-galactosidases, β-N-Acetylhexosaminidases and α-mannosidases.
Highlights
Capnocytophaga are capnophilic Gram negative bacteria that belong to the family of Flavobacteriaceae in the phylum Bacteroidetes and colonize the oral cavity of diverse mammals including humans [1,2]
C. canimorsus are able to escape complement killing and phagocytosis by human polymorphonuclear leukocytes (PMN’s) [10,11]. They escape detection and phagocytosis by macrophages, which results in a lack of release of proinflammatory cytokines [12]. In addition to this passive evasion from innate immunity, 60% of the strains are able to block the killing of Escherichia coli phagocytosed by macrophages [3,10] and some strains even block the onset of pro-inflammatory signalling induced by an E. coli lipopolysaccharide (LPS) stimulus [12]
A surprising feature of these bacteria is their capacity to feed by foraging the glycan moieties of glycoproteins from animal cells, including phagocytes
Summary
Capnocytophaga are capnophilic Gram negative bacteria that belong to the family of Flavobacteriaceae in the phylum Bacteroidetes and colonize the oral cavity of diverse mammals including humans [1,2]. Capnocytophaga canimorsus, a usual member of dog’s mouths flora [3,4], was discovered in 1976 [5] in patients that underwent dramatic infections after having been bitten, scratched or licked by a dog. These infections occur, worldwide, with an approximate frequency of one per million inhabitants per year. C. canimorsus are able to escape complement killing and phagocytosis by human polymorphonuclear leukocytes (PMN’s) [10,11] They escape detection and phagocytosis by macrophages, which results in a lack of release of proinflammatory cytokines [12]. This property was found to be dependent on a sialidase (SiaC) allowing C
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