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  • 2005-2009  (2)
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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: GspB and Hsa are homologous serine-rich surface glycoproteins of Streptococcus gordonii strains M99 and Challis, respectively, that mediate the binding of these organisms to platelet membrane glycoprotein (GP) Ibα. Both GspB and Hsa consist of an N-terminal putative signal peptide, a short serine-rich region, a region (BR) that is rich in basic amino acids, a longer serine-rich region and a C-terminal cell wall anchoring domain. To further assess the mechanisms for GspB and Hsa binding, we investigated the binding of the BRs of GspB and Hsa (expressed as glutathione S-tranferase fusion proteins) to sialylated glycoproteins in vitro. Both fusion proteins showed significant levels of binding to sialylated moieties on fetuin and GPIbα. In contrast, the corresponding region of a GspB homologue of Streptococcus agalactiae, which is acidic rather than basic, showed no binding to either fetuin or GPIbα. As measured by surface plasmon resonance kinetic analysis, GspB- and Hsa-derived fusion proteins had high affinity for GPIbα, but with somewhat different dissociation constants. Dot blot analysis using a panel of synthesized oligosaccharides revealed that the BR of Hsa can bind both α(2-3) sialyllactosamine [NeuAcα(2-3)Galβ(1-4)GlcNAc] and sialyl-T antigen [NeuAcα(2-3)Galβ(1-3)GalNAc], whereas the BR of GspB only bound sialyl-T antigen. Moreover, far Western blotting using platelet membrane proteins revealed that GPIbα is the principal receptor for GspB and Hsa on human platelets. The combined results indicate that the BRs of GspB and Hsa are the binding domains of these adhesins. However, the subsets of carbohydrate structures on GPIbα recognized by the binding domains appear to be different between the two proteins.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 58 (2005), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: GspB is a large cell-surface glycoprotein expressed by Streptococcus gordonii M99 that mediates binding of this organism to human platelets. This adhesin is glycosylated in the cytoplasm, and is then transported to the cell surface via an accessory Sec system. To assess the structural features of GspB that are needed for export, we examined the effects of altering the carbohydrate moieties or the polypeptide backbone of GspB. Truncated, glycosylated variants of GspB were exported exclusively via the accessory Sec pathway. When glycosylation was abolished, the GspB variants were still exported by this pathway, but minor amounts could also be transported by the canonical Sec system. GspB variants with in-frame insertions or deletions in the N-terminus were not secreted, indicating that this domain is necessary for export. However, the N-terminus is not sufficient for the transport of heterologous proteins, because C-terminal fusion of passenger proteins to this domain hindered export. In contrast, fusion of GspB to a canonical signal peptide resulted in the efficient export of non-glycosylated forms of the fusion protein via the canonical Sec pathway, whereas glycosylated forms could not be exported. Thus, the carbohydrate moieties and the atypical signal sequence of GspB interfere with export via the canonical pathway, and direct GspB towards the accessory Sec system.
    Type of Medium: Electronic Resource
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