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Infection and Immunity, November 2004, p. 6528-6537, Vol. 72, No. 11
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.11.6528-6537.2004

The Streptococcus gordonii Surface Proteins GspB and Hsa Mediate Binding to Sialylated Carbohydrate Epitopes on the Platelet Membrane Glycoprotein Ib{alpha}

Barbara A. Bensing,1 José A. López,2 and Paul M. Sullam1*

Division of Infectious Diseases, Veterans Affairs Medical Center and Department of Medicine, University of California, San Francisco, California,1 Thrombosis Research Section, Department of Medicine, Baylor College of Medicine and Veterans Affairs Medical Center, Houston, Texas2

Received 7 June 2004/ Returned for modification 14 July 2004/ Accepted 22 July 2004

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 {alpha}(2-3) or {alpha}(2-6) linkages, with a slight preference for {alpha}(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{alpha} (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.

* Corresponding author. Mailing address: Division of Infectious Diseases, VA Medical Center (111W), 4150 Clement St., San Francisco, CA 94121. Phone: (415) 221-4810, ext. 2550. Fax: (415) 750-0502. E-mail: sullam{at}itsa.ucsf.edu.

Editor: J. N. Weiser

Infection and Immunity, November 2004, p. 6528-6537, Vol. 72, No. 11
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.11.6528-6537.2004




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