PMID: 21205667 , Related PDB ids: 2XW9, 2XWA, 2XWB, 2XWJ

Authors:

Forneris F, Ricklin D, Wu J, Tzekou A, Wallace RS, Lambris JD, Gros P

Title:

Structures of C3b in complex with factors B and D give insight into complement convertase formation.

Journal:

Science. 2010 Dec 24;330(6012):1816-20.

Abstract:

Activation of the complement cascade induces inflammatory responses and marks cells for immune clearance. In the central complement-amplification step, a complex consisting of surface-bound C3b and factor B is cleaved by factor D to generate active convertases on targeted surfaces. We present crystal structures of the pro-convertase C3bB at 4 angstrom resolution and its complex with factor D at 3.5 angstrom resolution. Our data show how factor B binding to C3b forms an open "activation" state of C3bB. Factor D specifically binds the open conformation of factor B through a site distant from the catalytic center and is activated by the substrate, which displaces factor D's self-inhibitory loop. This concerted proteolytic mechanism, which is cofactor-dependent and substrate-induced, restricts complement amplification to C3b-tagged target cells.