Abstract
SummaryA range of Streptococcus bacteria are able to interact with blood platelets to form a thrombus (clot). Streptococcus gordonii is ubiquitous within the human oral cavity and amongst the common pathogens isolated from subjects with infective endocarditis. Two cell surface proteins, Hsa and Platelet adherence protein A (PadA), in S. gordonii mediate adherence and activation of platelets. In this study, we demonstrate that PadA binds activated platelets and that an NGR (Asparagine‐Glycine‐Arginine) motif within a 657 amino acid residue N‐terminal fragment of PadA is responsible for this, together with two other integrin‐like recognition motifs RGT and AGD. PadA also acts in concert with Hsa to mediate binding of S. gordonii to cellular fibronectin and vitronectin, and to promote formation of biofilms. Evidence is presented that PadA and Hsa are each reliant on the other's active presentation on the bacterial cell surface, suggesting cooperativity in functions impacting both colonization and pathogenesis.
Highlights
Streptococcus, Staphylococcus, and Enterococcus bacteria account for >80% cases of infective endocarditis (Muñoz et al, 2015; Slipczuk et al, 2013) and are able to trigger activation or aggregation of blood platelets into a clot or thrombus (Fitzgerald, Foster, & Cox, 2006; Kerrigan, 2015)
We have investigated the relative functions of Hsa and PadA in S. gordonii platelet interactions, and in bacterial cell binding to various extracellular matrix components that may be exposed at sites of endothelial damage, for example, fibronectin or vitronectin
We have studied in more detail the interactions of the mature N‐terminal F2 region (657 aa residues) of PadA with platelets and matrix components, and the relative roles of the integrin‐recognition motifs and NGR in S. gordonii host interactions
Summary
A range of Streptococcus bacteria are able to interact with blood platelets to form a thrombus (clot). Hsa and Platelet adherence protein A (PadA), in S. gordonii mediate adherence and activation of platelets. We demonstrate that PadA binds activated platelets and that an NGR (Asparagine‐ Glycine‐Arginine) motif within a 657 amino acid residue N‐terminal fragment of PadA is responsible for this, together with two other integrin‐like recognition motifs RGT and AGD. PadA acts in concert with Hsa to mediate binding of S. gordonii to cellular fibronectin and vitronectin, and to promote formation of biofilms. Evidence is presented that PadA and Hsa are each reliant on the other's active presentation on the bacterial cell surface, suggesting cooperativity in functions impacting both colonization and pathogenesis
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