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Substrate recognition by complement convertases revealed in the C5-cobra venom factor complex.

Nick S Laursen1, Kasper R Andersen, Ingke Braren

  • 1Department of Molecular Biology, Aarhus University, Aarhus, Denmark.

The EMBO Journal
|January 11, 2011
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Summary
This summary is machine-generated.

Complement system proteins C5 and cobra venom factor (CVF) form a two-point attachment. This interaction, influenced by inhibitor SSL7, reveals how convertases cleave complement proteins, aiding innate immunity.

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Area of Science:

  • Immunology
  • Structural Biology
  • Biochemistry

Background:

  • The complement system is crucial for innate immunity, initiating inflammation via C3 and C5 protein cleavage by convertases.
  • Convertases are complexes of substrate-binding and protease subunits (e.g., C3b-Bb).

Purpose of the Study:

  • To elucidate the structural basis of complement protein C5 cleavage by convertases.
  • To understand the mechanism of SSL7 inhibition on C5 cleavage.

Main Methods:

  • Determined crystal structures of cobra venom factor (CVF)-C5 and CVF-C5-SSL7 complexes at 4.3 Å resolution.
  • Analyzed protein-protein interactions and conformational changes.

Main Results:

  • Revealed a parallel two-point attachment between C5 and CVF.
  • Demonstrated SSL7's minimal impact on the C5-CVF interface, explaining IgA-dependent inhibition.
  • Showed CVF acts as a scaffold, inducing conformational changes in C5 for cleavage by Bb.

Conclusions:

  • Presented a general model for convertase substrate recognition based on C5-CVF and C3b-Bb-SCIN structures.
  • Rationalized prior knowledge of convertase-substrate interactions.