Sequential deglycosylation and utilization of the N-linked, complex-type glycans of human alpha(1)-acid glycoprotein mediates growth of Streptococcusoralis

Streptococcus oralis is the agent of a large number of infections in immuno compromised patients, but little is known regarding the mechanisms by which this fermentative organism proliferates in vivo. Glycoproteins are widespr ead within the circulation and host tissues, and could provide a source of fermentable carbohydrate for the growth of those pathogenic organisms with the capacity to release monosaccharides from glycans via the production of specific glycosidases, The ability of acute phase serum alpha(1)-acid glyco protein to support growth of S.oralis in vitro has been examined as a model for growth of this organism on N-linked glycoproteins, Growth was accompan ied by the production of a range of glycosidases (sialidase, N-acetyl-beta- D-glucosaminidase, and beta-D-galactosidase) as measured using the 4-methyl umbelliferone-linked substrates. The residual glycoprotein glycans remainin g during growth of this organism were released by treatment with hydrazine and their analysis by HPAEC-PAD and MALDI demonstrated extensive degradatio n of all glycan chains with only terminal N-acetylglucosamine residues atta ched to asparagines of the protein backbone remaining when growth was compl ete. Monosaccharides were released sequentially from the glycans by S.orali s glycosidases in the order sialic acid, galactose, fucose, nonterminal N-a cetylglucosamine, and mannose due to the actions of exo-glycosidic activiti es, including mannosidases which have not previously been reported for S.or alis, All released monosaccharides were metabolized during growth with the exception of fucose which remained free in culture supernatants, Direct rel ease of oligosaccharides was not observed, indicating the absence of endo-g lycosidases in S.oralis. We propose that this mechanism of deglycosylation of host glycoproteins and the subsequent utilization of released monosaccha rides is important in the survival and persistence of this and other pathog enic bacteria ill vivo.