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Role of Streptococcus gordonii Surface Proteins SspA/SspB and Hsa in Platelet Function

Molecular and Cellular Therapeutics, Royal College of Surgeons in Ireland, Dublin 2, Ireland,¹ Department of Oral and Dental Science, University of Bristol, Bristol BS1 2LY, United Kingdom,² School of Medicine and Medical Science, Conway Institute for Biomolecular and Biomedical Sciences, University College Dublin, Dublin 4, Ireland³

Received 5 July 2007/ Returned for modification 6 August 2007/ Accepted 13 September 2007

Streptococcus gordonii colonization of damaged heart surfaces in infective endocarditis is dependent upon the recognition of host receptors by specific bacterial surface proteins. However, despite several attempts to identify the mechanisms involved in this interaction, the nature of the bacterial proteins required remains poorly understood. This study provides clear evidence that several S. gordonii surface proteins participate in the interaction with platelets to support platelet adhesion and induce platelet aggregation. S. gordonii strains were found to support strong (DL1-Challis, SK12, SK184, and Blackburn) or moderate (UB1545 hsa and CH1-Challis) adhesion or failed to support platelet adhesion (M5, M99, and Channon). In addition, under flow conditions, platelets rolled and subsequently adhered to immobilized S. gordonii at low shear (50 s^–1) in an Hsa-dependent manner but did not interact with S. gordonii DL1 at any shear rate of >50 s^–1. S. gordonii strains either induced (DL1-Challis, SK12, SK184, UB1545 hsa, and M99) or failed to induce (M5, CH1-Challis, Channon, and Blackburn) platelet aggregation. Using a proteomic approach to identify differential cell wall protein expression between aggregating (DL1) and nonaggregating (Blackburn) strains, we identified antigen I/antigen II family proteins SspA and SspB. The overexpression of SspA or SspB in platelet-nonreactive Lactococcus lactis induced GPIIb/GPIIIa-dependent platelet aggregation similar to that seen with S. gordonii DL1. However, they failed to support platelet adhesion. Thus, S. gordonii has distinct mechanisms for supporting platelet adhesion and inducing platelet aggregation. Differential protein expression between strains may be important for the pathogenesis of invasive diseases such as infective endocarditis.

Published ahead of print on 24 September 2007.

Editor: B. A. McCormick