PMID: 15016353 , Related PDB id: 1Q0P

Authors:

Bhattacharya AA, Lupher ML Jr, Staunton DE, Liddington RC

Title:

Crystal structure of the A domain from complement factor B reveals an integrin-like open conformation.

Journal:

Structure. 2004 Mar;12(3):371-8.

Abstract:

Complement factor B is a 90 kDa protein consisting of three domains: a three-module complement control protein, a von Willebrand factor A domain, and a C-terminal serine protease (SP) domain that adopts a default inactive (zymogen) conformation. The interaction between factor B and pathogen-bound C3b is mediated by its A domain, triggering a conformational change in factor B that ultimately creates the "C3 convertase" of the alternative complement pathway. We report the crystal structure of the A domain from factor B and show that it contains an integrin-like MIDAS motif that adopts the "open" conformation typical of integrin-ligand complexes, with an acidic residue (provided by a fortuitous crystal contact) completing the coordination of the metal ion. Modeling studies indicate that the factor B A domain can also adopt the closed conformation, supporting the hypothesis that an "integrin-like switch" is conserved in complement proteins and perhaps in 60 other A domains found within the human proteome.