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Related Experiment Videos

The binding site for C1q on IgG.

A R Duncan1, G Winter

  • 1MRC Laboratory of Molecular Biology, Cambridge, UK.

Nature
|April 21, 1988
PubMed
Summary
This summary is machine-generated.

Antibodies initiate pathogen clearance by binding antigens and activating complement. Researchers identified specific amino acids (Glu 318, Lys 320, Lys 322) in the antibody Fc region crucial for C1q binding and complement activation.

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Area of Science:

  • Immunology
  • Molecular Biology
  • Biochemistry

Background:

  • Antibodies are key in humoral immunity, mediating pathogen clearance through mechanisms like complement lysis.
  • The complement cascade initiates with C1q binding to the antibody Fc region, a process sensitive to ionic strength and conserved across species.
  • Initial C1q binding to isolated antibody Fc regions is weak, but multivalent binding significantly enhances affinity.

Purpose of the Study:

  • To precisely map the C1q binding site on the antibody Fc region.
  • To identify specific amino acid residues involved in the C1q-antibody interaction.
  • To investigate the functional significance of the identified binding site in complement activation.

Main Methods:

  • Systematic mutagenesis of surface residues in the mouse IgG2b isotype.

Related Experiment Videos

  • Analysis of C1q binding affinities to altered antibody variants.
  • Testing the efficacy of a peptide mimic of the identified binding site in inhibiting complement lysis.

    • Main Results:

    • Localized the C1q binding site to three specific side chains: Glu 318, Lys 320, and Lys 322 in the mouse IgG2b Fc region.
    • These residues are conserved in other antibody isotypes.
    • A peptide mimicking this sequence motif effectively inhibited complement lysis.

    Conclusions:

    • The identified sequence motif (Glu 318, Lys 320, Lys 322) represents a critical binding site for C1q on IgG antibodies.
    • This conserved motif is essential for initiating the classical complement pathway.
    • The findings provide a molecular basis for C1q-antibody interactions and potential therapeutic targeting.