Interaction with human plasminogen system turns on proteolytic activity in Streptococcus agalactiae and enhances its virulence in a mouse model

Interactions of several microbial pathogens with the plasminogen system increase their invasive potential. In this study, we show that Streptococcus agalactiae binds human plasminogen which can be subsequently activated to plasmin, thus generating a proteolytic bacterium. S. agalactiae binds plasminogen via the direct pathway, using plasminogen receptors, and via the indirect pathway through fibrinogen receptors. The glyceraldehyde-3-phosphate dehydrogenase is one If the S. agalactiae proteins that bind plasminogen. Presence of exogenous activators such as uPA and tPA are required to activate bound plasminogen. Results from competitive inhibition assays indicate that binding is partially mediated through the lysine binding sites of plasminogen. Following plasminogen binding and activation, S. agalactiae is able to degrade in vitro fibronectin, one of the host extracellular matrix proteins. Moreover, incubation of S. agalactiae with either plasminogen alone, or plasminogen plus fibrinogen, in the presence of tPA enhanced its virulence in C57BL/6 mice, suggesting that acquisition of plasmin-like activity by the bacteria increase their invasiveness

Interaction with human plasminogen system turns on proteolytic activity in Streptococcus agalactiae and enhances its virulence in a mouse model

Interactions of several microbial pathogens with the plasminogen system increase their invasive potential. In this study, we show that Streptococcus agalactiae binds human plasminogen which can be subsequently activated to plasmin, thus generating a proteolytic bacterium. S. agalactiae binds plasminogen via the direct pathway, using plasminogen receptors, and via the indirect pathway through fibrinogen receptors. The glyceraldehyde-3-phosphate dehydrogenase is one If the S. agalactiae proteins that bind plasminogen. Presence of exogenous activators such as uPA and tPA are required to activate bound plasminogen. Results from competitive inhibition assays indicate that binding is partially mediated through the lysine binding sites of plasminogen. Following plasminogen binding and activation, S. agalactiae is able to degrade in vitro fibronectin, one of the host extracellular matrix proteins. Moreover, incubation of S. agalactiae with either plasminogen alone, or plasminogen plus fibrinogen, in the presence of tPA enhanced its virulence in C57BL/6 mice, suggesting that acquisition of plasmin-like activity by the bacteria increase their invasiveness

Identification of NAD(+) Synthetase from Streptococcus sobrinus as a B-Cell-Stimulatory Protein

Streptococcus sobrinus, one agent of dental caries, secretes a protein that induces lymphocyte polyclonal activation of the host as a mechanism of immune evasion. We have isolated from culture supernatants of this bacterium a protein with murine B-cell-stimulatory properties and subsequently cloned the relevant gene. It contains an open reading frame of 825 bp encoding a polypeptide with 275 amino acid residues and a molecular mass of 30 kDa. The protein displays high sequence homology with NAD(+) synthetases from several organisms, including a conserved fingerprint sequence (SGGXD) characteristic of ATP pyrophosphatases. The polypeptide was expressed in Escherichia coli as a hexahistidine-tagged protein and purified in an enzymatically active form. The recombinant NAD(+) synthetase stimulates murine B cells after in vitro treatment of spleen cell cultures, as demonstrated by its ability to induce up-regulation of the expression of CD69, an early marker of lymphocyte activation. Stimulation with the recombinant NAD(+) synthetase was also observed with other B-cell markers, such as CD19(+), B220(+), and CD21(+). Cell proliferation follows the activation induced by the recombinant NAD(+) synthetase