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A theoretical view of the C3d:CR2 binding controversy
Rohith R Mohan1, Ronald D Gorham1, Dimitrios Morikis1
1Department of Bioengineering, University of California, Riverside, United States.
Molecular Immunology
|December 1, 2014
Summary
The C3d:CR2 interaction
Area of Science:
- Immunology
- Structural Biology
- Computational Biophysics
Background:
- The complement system protein C3d binds to CR2 (Complement Receptor 2), bridging innate and adaptive immunity.
- Conflicting cocrystal structures (PDB: 1GHQ and 3OED) have created debate regarding the C3d:CR2 binding mode.
- The 1GHQ structure shows CR2 SCR2 binding C3d's side face, while 3OED shows CR2 SCR1-2 binding C3d's acidic patch.
Purpose of the Study:
- To computationally investigate the binding modes of the C3d:CR2 interaction.
- To determine the electrostatically and energetically favorable binding site for C3d:CR2.
- To explain the influence of nonphysiological zinc ions on C3d:CR2 complex formation.
Main Methods:
- Utilized a variety of computational approaches.
- Analyzed electrostatic favorability, structural and dissociative stability, and binding affinity.
- Investigated the effect of nonphysiological zinc ions on binding.
Main Results:
- The acidic patch binding site (3OED mode) is electrostatically more favorable, more stable, and has higher binding affinity than the 1GHQ mode.
- Nonphysiological zinc ions enhance C3d:CR2 complex formation at C3d's side face (1GHQ mode).
- Zinc ions increase electrostatic favorability, intermolecular interactions, and overall energetic favorability for the 1GHQ binding mode.
Conclusions:
- Provides a theoretical basis for C3d:CR2 binding at C3d's acidic cavity.
- Explains CR2 binding to C3d's side face in the presence of nonphysiological zinc ions.
- Clarifies the binding mechanisms of the C3d:CR2 interaction under different conditions.
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