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Staphylococcal complement inhibitor modulates phagocyte responses by dimerization of convertases.

Ilse Jongerius1, Manon Puister, Jin Wu

  • 1Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands. i.jongerius@umcutrecht.nl

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Staphylococcus aureus uses staphylococcal complement inhibitor (SCIN) to evade immune detection by forming dimeric complement enzymes. This dimerization impairs binding to key phagocytic receptors, aiding bacterial survival.

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Area of Science:

  • Microbiology
  • Immunology
  • Structural Biology

Background:

  • Staphylococcus aureus is a human pathogen that employs complement-evasion molecules to resist host immunity.
  • The staphylococcal complement inhibitor (SCIN) is a key molecule that targets complement C3 convertase enzymes, crucial for complement-mediated functions like phagocytosis and inflammation.
  • SCIN inhibits the alternative pathway C3 convertase (C3bBb) and induces its dimerization.

Purpose of the Study:

  • To investigate the role of SCIN-induced dimerization of C3 convertases in Staphylococcus aureus immune evasion.
  • To determine how SCIN-mediated dimerization affects the recognition of complement-coated bacteria by phagocytic receptors.

Main Methods:

  • Biochemical assays to study the interaction of SCIN with C3 convertases.
  • Analysis of the binding of monomeric and dimeric SCIN-convertase complexes to complement receptors.
  • Assessment of the antiphagocytic properties of SCIN.

Main Results:

  • SCIN induces dimerization of the alternative pathway C3 convertase (C3bBb).
  • Dimeric SCIN-convertase complexes exhibit impaired binding to complement receptor 1 (CR1) and the complement receptor of the Ig superfamily (CRIg).
  • The dimerization site of SCIN is critical for its potent antiphagocytic activity.

Conclusions:

  • SCIN-induced dimerization of C3 convertases is a novel immune evasion strategy employed by Staphylococcus aureus.
  • This dimerization mechanism hinders the recognition of bacteria by key phagocytic receptors, contributing to immune evasion.
  • Understanding SCIN's mechanism provides insights into Staphylococcus aureus pathogenesis and potential therapeutic targets.