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Structure of complement fragment C3b-factor H and implications for host protection by complement regulators.

Jin Wu¹, You-Qiang Wu, Daniel Ricklin

¹Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Department of Chemistry, Utrecht University, Utrecht, The Netherlands.

Nature Immunology

|June 9, 2009

Summary

Factor H (FH) regulates complement activation by binding complement fragment C3b. This structural study reveals how FH destabilizes the C3 convertase and aids C3b degradation, explaining disease mutations.

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Area of Science:

Immunology
Structural Biology
Biochemistry

Background:

Factor H (FH) is a key regulator of the complement system.
FH protects host cells from complement-mediated damage.
Dysregulation of complement contributes to various diseases.

Purpose of the Study:

To elucidate the structural basis of Factor H's regulatory activity.
To understand the interaction between FH and its target, complement fragment C3b.
To provide insights into disease-related mutations.

Main Methods:

X-ray crystallography was used to solve the structure of FH domains 1-4 bound to C3b.
Structural analysis of the FH-C3b complex.

Main Results:

FH binds to multiple domains of C3b, covering an extensive surface area.
FH destabilizes the C3 convertase through competition and electrostatic repulsion.
FH acts as a platform for Factor I-mediated C3b degradation and stabilizes C3b.

Conclusions:

The study provides a structural model for complement regulation by FH.
The findings offer explanations for mutations in FH and C3b linked to diseases.
This work deepens our understanding of the complement system's intricate regulatory mechanisms.