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Related Experiment Video

Updated: Jun 22, 2026

High-resolution Melting PCR for Complement Receptor 1 Length Polymorphism Genotyping: An Innovative Tool for Alzheimer's Disease Gene Susceptibility Assessment
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Multimeric interactions between complement factor H and its C3d ligand provide new insight on complement regulation.

Azubuike I Okemefuna1, Keying Li, Ruodan Nan

  • 1Institute of Structural and Molecular Biology, Division of Biosciences Darwin Building, University College London, Gower Street, London, UK.

Journal of Molecular Biology
|June 10, 2009
PubMed
Summary
This summary is machine-generated.

Factor H (FH) and its fragment C3d form multimeric complexes, not a simple 1:1 binding. This finding offers new insights into complement regulation at host cell surfaces during excessive complement activation.

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Published on: January 29, 2014

Area of Science:

  • Immunology
  • Biochemistry
  • Structural Biology

Background:

  • The alternative complement pathway is initiated by C3b activation.
  • Factor H (FH) is the primary serum regulator of C3b.
  • The C-terminal SCR-20 domain of FH binds C3d, a fragment of C3b.

Purpose of the Study:

  • To investigate the binding stoichiometry and complex formation between FH (or its fragment SCR-16/20) and C3d.
  • To elucidate the structural basis of FH-C3d interactions.
  • To provide new insights into FH regulation during complement activation.

Main Methods:

  • Analytical ultracentrifugation to analyze size distribution of FH/SCR-16/20 and C3d mixtures.
  • Surface plasmon resonance to study binding kinetics and determine equilibrium dissociation constants.
  • X-ray scattering to assess the dimensions of C3d complexes with SCR-16/20.
  • Molecular modeling to interpret structural data.

Main Results:

  • Multimeric complexes of FH/SCR-16/20 and C3d were observed at physiologically relevant concentrations.
  • Surface plasmon resonance revealed a two-stage binding process with a K(D)(1) of 2.6 microM for the initial interaction.
  • X-ray scattering and molecular modeling suggest the formation of associating dimers.
  • The interaction is not a simple 1:1 stoichiometry as commonly assumed.

Conclusions:

  • The physiological interaction between FH and C3d involves multimer formation, challenging the traditional 1:1 binding model.
  • These multimers involve the C-terminus of FH, impacting its interaction with host cell surfaces.
  • The findings offer novel perspectives on FH's regulatory role in both fluid-phase and cell-surface complement activation.