• Bifidobacterial enolase, a cell surface receptor for human plasminogen involved in the interaction with the host.

      Candela, Marco; Biagi, Elena; Centanni, Manuela; Turroni, Silvia; Vici, Manuela; Musiani, Francesco; Vitali, Beatrice; Bergmann, Simone; Hammerschmidt, Sven; Brigidi, Patrizia; et al. (2009-10)
      The interaction with the host plasminogen/plasmin system represents a novel component in the molecular cross-talk between bifidobacteria and human host. Here, we demonstrated that the plasminogen-binding bifidobacterial species B. longum, B. bifidum, B. breve and B. lactis share the key glycolytic enzyme enolase as a surface receptor for human plasminogen. Enolase was visualized on the cell surface of the model strain B. lactis BI07. The His-tagged recombinant protein showed a high affinity for human plasminogen, with an equilibrium dissociation constant in the nanomolar range. By site-directed mutagenesis we demonstrated that the interaction between the B. lactis BI07 enolase and human plasminogen involves an internal plasminogen-binding site homologous to that of pneumococcal enolase. According to our data, the positively charged residues Lys-251 and Lys-255, as well as the negatively charged Glu-252, of the B. lactis BI07 enolase are crucial for plasminogen binding. Acting as a human plasminogen receptor, the bifidobacterial surface enolase is suggested to play an important role in the interaction process with the host.
    • Contribution of plasminogen activation towards the pathogenic potential of oral streptococci.

      Itzek, Andreas; Gillen, Christine M; Fulde, Marcus; Friedrichs, Claudia; Rodloff, Arne C; Chhatwal, Gursharan S; Nitsche-Schmitz, Daniel Patric; Department of Medical Microbiology, Helmholtz Centre for Infection Research, Braunschweig, Germany. (2010)
      Oral streptococci are a heterogeneous group of human commensals, with a potential to cause serious infections. Activation of plasminogen has been shown to increase the virulence of typical human pathogenic streptococci such as S. pneumoniae. One important factor for plasminogen activation is the streptococcal α-enolase. Here we report that plasminogen activation is also common in oral streptococci species involved in clinical infection and that it depends on the action of human plasminogen activators. The ability to activate plasminogen did not require full conservation of the internal plasminogen binding sequence motif FYDKERKVY of α-enolase that was previously described as crucial for increased plasminogen binding, activation and virulence. Instead, experiments with recombinant α-enolase variants indicate that the naturally occurring variations do not impair plasminogen binding. In spite of these variations in the internal plasminogen binding motif oral streptococci showed similar activation of plasminogen. We conclude that the pathomechanism of plasminogen activation is conserved in oral streptococci that cause infections in human. This may contribute to their opportunistic pathogenic character that is unfurled in certain niches.
    • Cooperative binding and activation of fibronectin by a bacterial surface protein.

      Marjenberg, Zoe R; Ellis, Ian R; Hagan, Robert M; Prabhakaran, Sabitha; Höök, Magnus; Talay, Susanne R; Potts, Jennifer R; Staunton, David; Schwarz-Linek, Ulrich; Biomedical Sciences Research Complex, University of St. Andrews, St. Andrews KY16 9ST, Scotland, United Kingdom. (2011-01-21)
      Integrin-dependent cell invasion of some pathogenic bacteria is mediated by surface proteins targeting the extracellular matrix protein fibronectin (FN). Although the structural basis for bacterial FN recognition is well understood, it has been unclear why proteins such as streptococcal SfbI contain several FN-binding sites. We used microcalorimetry to reveal cooperative binding of FN fragments to arrays of binding sites in SfbI. In combination with thermodynamic analyses, functional cell-based assays show that SfbI induces conformational changes in the N-terminal 100-kDa region of FN (FN100kDa), most likely by competition with intramolecular interactions defining an inactive state of FN100kDa. This study provides insights into how long range conformational changes resulting in FN activation may be triggered by bacterial pathogens.
    • SCM, a novel M-like protein from Streptococcus canis, binds (mini)-plasminogen with high affinity and facilitates bacterial transmigration.

      Fulde, Marcus; Rohde, Manfred; Hitzmann, Angela; Preissner, Klaus T; Nitsche-Schmitz, D Patric; Nerlich, Andreas; Chhatwal, Gursharan Singh; Bergmann, Simone; Department of Medical Microbiology, Helmholtz Centre for Infection Research (HZI), Braunschweig, Germany. Marcus.Fulde@helmholtz-hzi.de (2011-02-24)
      Streptococcus canis is an important zoonotic pathogen capable of causing serious invasive diseases in domestic animals and humans. In the present paper we report the binding of human plasminogen to S. canis and the recruitment of proteolytically active plasmin on its surface. The binding receptor for plasminogen was identified as a novel M-like protein designated SCM (S. canis M-like protein). SPR (surface plasmon resonance) analyses, radioactive dot-blot analyses and heterologous expression on the surface of Streptococcus gordonii confirmed the plasminogen-binding capability of SCM. The binding domain was located within the N-terminus of SCM, which specifically bound to the C-terminal part of plasminogen (mini-plasminogen) comprising kringle domain 5 and the catalytic domain. In the presence of urokinase, SCM mediated plasminogen activation on the bacterial surface that was inhibited by serine protease inhibitors and lysine amino acid analogues. Surface-bound plasmin effectively degraded purified fibrinogen as well as fibrin clots, resulting in the dissolution of fibrin thrombi. Electron microscopic illustration and time-lapse imaging demonstrated bacterial transmigration through fibrinous thrombi. The present study has led, for the first time, to the identification of SCM as a novel receptor for (mini)-plasminogen mediating the fibrinolytic activity of S. canis.