The Streptococcus gordonii Surface Proteins GspB and Hsa Mediate Binding to Sialylated Carbohydrate Epitopes on the Platelet Membrane Glycoprotein Ibα

Abstract

Platelet binding by Streptococcus gordonii strain M99 is dependent on expression of the cell wall-anchored glycoprotein GspB. This large cell surface protein is exported from the M99 cytoplasm via a dedicated transport system that includes SecA2 and SecY2. GspB is highly similar to Hsa, a protein expressed by S. gordonii Challis that has been characterized as a sialic acid binding hemagglutinin. In this study, we compared the contribution of GspB and Hsa to the adherence of S. gordonii to selected glycoproteins. Our results indicate that GspB can mediate binding to a variety of sialylated glycoproteins. GspB facilitates binding to carbohydrates bearing sialic acid in either ␣(2-3) or ␣(2-6) linkages, with a slight preference for ␣(2-3) linkages. Furthermore, GspB readily mediates binding to sialic acid residues on immobilized glycocalicin, the extracellular portion of the platelet membrane glycoprotein (GP) Ib␣ (the ligand binding subunit of the platelet von Willebrand factor receptor complex GPIb-IX-V). Although Hsa is required for the binding of S. gordonii Challis to sialic acid, most of the Hsa expressed by Challis is retained in the cytoplasm. The deficiency in export is due, at least in part, to a nonsense mutation in secA2. Hsa export can be enhanced by complementation with secA2 from M99, which also results in significantly greater binding to sialylated glycoproteins, including glycocalicin. The combined results indicate that GspB and Hsa contribute similar binding capabilities to M99 and Challis, respectively, but there may be subtle differences in the preferred epitopes to which these adhesins bind.

Roles of Brucella abortus SpoT in morphological differentiation and intramacrophagic replication

“…The question is raised why the B. abortus spoT mutant showed the same LPS profiles but a fourfold higher adherence to macrophages than wildtype. In many cases, adherence is mediated by one or more adhesins that can act simultaneously or in distinct steps during the infection process (Finlay & Falkow, 1997 (Bensing et al, 2004) are related to adherence to host cells. Analysis of the genome sequence of Brucella has revealed various genes encoding putative adhesion and invasion mechanisms involved in attachment and actin recruitment in cells, yet no fimbrial or non-fimbrial adhesion has been described in the genus Brucella (DelVecchio et al, 2002).…”

Clinical isolates of Enterococcus faecalis aggregate human platelets

“…Direct interactions between bacteria and platelets can also occur. A surface protein from Streptococcus sanguis or Streptococcus gordonii can bind directly to the platelet surface, but to mediate aggregation bacteria specific IgG is also required [10,11]. A slower form of aggregation occurs for S. aureus through interactions with specific IgG and complement which induce platelet aggregation after a longer lagtime [6].…”

Mechanism of a cytosolic O -glycosyltransferase essential for the synthesis of a bacterial adhesion protein

“…These adhesins contain serine-rich repeats (SRR) that are heavily modified. The glycoproteins are exported from the cell, but remain associated with the cell wall and allow the bacteria to attach to the host cells and their surrounding extracellular matrix (10)(11)(12)(13)(14)(15)(16)(17). In addition, SRR glycoproteins may also mediate interactions between bacteria, facilitating biofilm formation and bacterial colonization (18).…”