Molecular characterization of the multiple interactions of SpsD, a surface protein from Staphylococcus pseudintermedius, with host extracellular matrix proteins

Staphylococcus pseudintermedius, a commensal and pathogen of dogs and occasionally of humans, expresses surface
proteins potentially involved in host colonization and pathogenesis. Here, we describe the cloning and characterization of
SpsD, a surface protein of S. pseudintermedius reported as interacting with extracellular matrix proteins and corneocytes. A
ligand screen and Western immunoblotting revealed that the N-terminal A domain of SpsD bound fibrinogen, fibronectin,
elastin and cytokeratin 10. SpsD also interfered with thrombin-induced fibrinogen coagulation and blocked ADP-induced
platelet aggregation. The binding site for SpsD was mapped to residues 395–411 in the fibrinogen c-chain, while binding
sites in fibronectin were localized to the N- and C-terminal regions. SpsD also bound to glycine- and serine-rich omega loops
within the C-terminal tail region of cytokeratin 10. Ligand binding studies using SpsD variants lacking the C-terminal
segment or containing an amino-acid substitution in the putative ligand binding site provided insights into interaction
mechanism of SpsD with the different ligands. Together these data demonstrate the multi-ligand binding properties of
SpsD and illustrate some interesting differences in the variety of ligands bound by SpsD and related proteins from S. aureus