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Effects of zinc on factor I cofactor activity of C4b-binding protein and factor H

Anna M Blom1, Lena Kask, Bala Ramesh

  • 1Department of Clinical Chemistry, Lund University, University Hospital Malmö, S-205 02, Malmö, Sweden. Anna.Blom@klkemi.mas.lu.se

Archives of Biochemistry and Biophysics
|October 3, 2003
PubMed

Insights

Zinc ions enhance complement inhibition by increasing cofactor affinity for C3b/C4b at low concentrations. High zinc levels cause aggregation, inhibiting this crucial immune process.

Area of Science:

  • Immunology
  • Biochemistry

Background:

  • Complement inhibition is vital for immune system regulation.
  • Factor I (FI) proteolytically degrades complement factors C3b and C4b.
  • Cofactor proteins are essential for Factor I-mediated degradation.

Purpose of the Study:

  • To investigate the role of zinc ions (Zn2+) in complement inhibition.
  • To determine how zinc affects the cofactor activity of C4b-binding protein and factor H.

Main Methods:

  • Surface plasmon resonance to assess protein-ligand interactions.
  • Fluorescent chelator method to determine zinc binding constants.
  • Nitrocellulose membrane immobilization for protein binding studies.

Main Results:

  • Zinc ions (Zn2+) at micromolar concentrations enhance cofactor activity.
  • High zinc concentrations (≥2 mM) abolish cofactor activity.
  • Zinc binds to C3b and C4b, increasing their affinity for cofactors at low zinc levels.
  • High zinc concentrations induce aggregation of C4b/C3b, inhibiting the reaction.

Conclusions:

  • Zinc ions modulate complement inhibition by regulating cofactor activity.
  • Low zinc concentrations enhance complement regulation, while high concentrations impair it.
  • Understanding zinc's role is crucial for therapeutic strategies targeting the complement system.

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