4e0s | pdb_00004e0s
Crystal Structure of C5b-6
Structural highlights
Disease[CO6_HUMAN] Defects in C6 are the cause of complement component 6 deficiency (C6D) [MIM:612446]. A rare defect of the complement classical pathway associated with susceptibility to severe recurrent infections, predominantly by Neisseria gonorrhoeae or Neisseria meningitidis. Function[CO6_HUMAN] Constituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. Publication Abstract from PubMedThe complement Membrane Attack Complex (MAC) forms transmembrane pores in pathogen membranes. The first step in MAC assembly is cleavage of C5 to generate metastable C5b, which forms a stable complex with C6, termed C5b-6. C5b-6 initiates pore formation via the sequential recruitment of homologous proteins: C7, C8, and 12-18 copies of C9, each of which comprise a central MACPF domain flanked by auxiliary domains. We recently proposed a model of pore assembly, in which the auxiliary domains play key roles, both in stabilizing the closed conformation of the protomers, and in driving the sequential opening of the MACPF beta-sheet of each new recruit to the growing pore. Here, we describe an atomic model of C5b-6 at 4.2 A resolution. We show that C5b provides 4 interfaces for the auxiliary domains of C6. The largest interface is created by the insertion of an interdomain linker from C6 into a hydrophobic groove created by a major reorganization of the alpha-helical domain of C5b. In combination with a rigid-body docking of N-terminal elements of both proteins, C5b becomes locked into a stable conformation. Both C6 auxiliary domains flanking the linker pack tightly against C5b. The net effect is to induce a clockwise rigid-body rotation of 4 auxiliary domains as well as an opening/twisting of the central beta-sheet of C6, in the directions predicted by our model to activate or prime C6 for the subsequent steps in MAC assembly. The complex also suggests novel small-molecule strategies for modulating pathological MAC assembly. Crystal structure of C5b-6 suggests a structural basis for priming the assembly of the Membrane Attack Complex (MAC).,Aleshin AE, Discipio RG, Stec B, Liddington RC J Biol Chem. 2012 Apr 12. PMID:22500023[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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