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Insights into complement convertase formation based on the structure of the factor B‐cobra venom factor complex
Author(s) -
Janssen Bert J C,
Gomes Lucio,
Koning Roman I,
Svergun Dmitri I,
Koster Abraham J,
Fritzinger David C,
Vogel CarlWilhelm,
Gros Piet
Publication year - 2009
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/emboj.2009.184
Subject(s) - c3 convertase , complement factor b , biology , cobra , alternative complement pathway , ophidia , complement system , complement (music) , complement factor i , venom , immunology , genetics , biochemistry , antibody , phenotype , gene , complementation , computer science , programming language
Immune protection by the complement system critically depends on assembly of C3 convertases on the surface of pathogens and altered host cells. These short‐lived protease complexes are formed through pro‐convertases, which for the alternative pathway consist of the complement component C3b and the pro‐enzyme factor B (FB). Here, we present the crystal structure at 2.2‐Å resolution, small‐angle X‐ray scattering and electron microscopy (EM) data of the pro‐convertase formed by human FB and cobra venom factor (CVF), a potent homologue of C3b that generates more stable convertases. FB is loaded onto CVF through its pro‐peptide Ba segment by specific contacts, which explain the specificity for the homologous C3b over the native C3 and inactive products iC3b and C3c. The protease segment Bb binds the carboxy terminus of CVF through the metal‐ion dependent adhesion site of the Von Willebrand factor A‐type domain. A possible dynamic equilibrium between a ‘loading’ and ‘activation’ state of the pro‐convertase may explain the observed difference between the crystal structure of CVFB and the EM structure of C3bB. These insights into formation of convertases provide a basis for further development of complement therapeutics.