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The pH-regulated antigen 1 of Candida albicans binds the human complement inhibitor C4b-binding protein and mediates

Shanshan Luo1, Anna M Blom2, Steffen Rupp3

  • 1From the Department of Infection Biology and.

The Journal of Biological Chemistry
|January 8, 2011
PubMed

Insights

Candida albicans uses Pra1 to bind human C4b-binding protein (C4BP), evading the immune system. This interaction helps the fungus evade complement-mediated destruction.

Area of Science:

  • Immunology
  • Microbiology
  • Biochemistry

Background:

  • Candida albicans employs immune evasion strategies to survive in the host.
  • Human complement inhibitors like C4b-binding protein (C4BP) are crucial targets for microbial immune evasion.

Purpose of the Study:

  • To identify and characterize the interaction between Candida albicans pH-regulated antigen 1 (Pra1) and human C4BP.
  • To determine the role of the Pra1-C4BP interaction in Candida albicans immune evasion.

Main Methods:

  • Enzyme-linked immunosorbent assay (ELISA)
  • Isothermal titration calorimetry (ITC)
  • Recombinant protein expression
  • Candida albicans strain manipulation (overexpression and knockout)

Main Results:

  • Pra1 directly binds C4BP through ionic interactions.
  • Binding sites were localized to CCP4, CCP7, and CCP8 domains of C4BP.
  • C4BP bound to Pra1 retains its complement-inhibitory activity.
  • Pra1 facilitates simultaneous binding of C4BP and Factor H.
  • Pra1 overexpression enhances C4BP surface deposition on C. albicans, while Pra1 knockout reduces it.
  • C4BP captured by C. albicans inhibits complement deposition (C4b, C3b) and maintains cofactor activity.

Conclusions:

  • Candida Pra1 is the first identified fungal protein that binds C4BP.
  • Pra1 binding to C4BP mediates human complement control, aiding Candida albicans immune and complement evasion.

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