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Ionic tethering contributes to the conformational stability and function of complement C3b.

Andrés López-Perrote1, Reed E S Harrison2, Marta Subías3

  • 1Centro de Investigaciones Biológicas, Spanish National Research Council (CSIC), Madrid, Spain.

Molecular Immunology
|March 4, 2017
PubMed
Summary
This summary is machine-generated.

The complement protein C3b

Keywords:
C3bComplementElectron microscopyF-variantPolymorphismsS-variant

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Area of Science:

  • Immunology
  • Structural Biology
  • Computational Biology

Background:

  • The complement system's alternative pathway (AP) is crucial for immune response.
  • C3b, a key component, exists in multiple conformations affecting protein interactions.
  • Understanding C3b's conformational dynamics is vital for complement regulation research.

Purpose of the Study:

  • To investigate the conformational dynamics of C3b using computational and molecular imaging techniques.
  • To elucidate the role of electrostatic interactions in C3b's structural stability.
  • To explore how C3b conformation influences its interaction with Factor B and complement regulation.

Main Methods:

  • Development of a computational model for electrostatic interactions within C3b.
  • Application of single-molecule electron microscopy (EM) for molecular imaging.
  • Thermodynamic modeling to assess the impact of counterion concentration on C3b structure.

Main Results:

  • Identified an ionic tether between C3b's TED domain and its MG ring.
  • Demonstrated NaCl concentration-dependent conformational changes in C3b via EM.
  • Showed TED domain displacement is compatible with C3b-Factor B binding.
  • Predicted mutations, including the R102G polymorphism, affect TED domain positioning.
  • Observed distinct conformational differences between C3b isoforms (C3bS and C3bF).

Conclusions:

  • C3b's TED domain exhibits an ionic, reversible attachment to the MG ring.
  • This conformational flexibility may influence complement regulation, particularly in specific C3b polymorphisms.
  • The findings provide insights into C3b structure-function relationships and potential therapeutic targets.