Activation of C5 by a C5 convertase initiates the spontaneous assembly of the late complement components, C5-C9, into the membrane attack complex. C5b has a transient binding site for C6. The C5b-C6 complex is the foundation upon which the lytic complex is assembled. Derived from proteolytic degradation of complement C5, C5a anaphylatoxin is a mediator of local inflammatory process. Binding to the receptor C5AR1 induces a variety of responses including intracellular calcium release, contraction of smooth muscle, increased vascular permeability, and histamine release from mast cells and basophilic leukocytes (PubMed:8182049). C5a is also a potent chemokine which stimulates the locomotion of polymorphonuclear leukocytes and directs their migration toward sites of inflammation. C5 precursor is first processed by the removal of 4 basic residues, forming two chains, beta and alpha, linked by a disulfide bond. C5 convertase activates C5 by cleaving the alpha chain, releasing C5a anaphylatoxin and generating C5b (beta chain + alpha' chain). Interacts with the tick complement inhibitors OmCI, RaCI1 and CirpT1 (PubMed:18536718, PubMed:27018802, PubMed:31871188). Interacts with cobra venom factor (CVF) (PubMed:21217642). Interacts with C5AR1. (Microbial infection) Interacts with Staphylococcus aureus protein SSL5. C5 variants are responsible for poor response to eculizumab [MIM:615749]. Eculizumab is a monoclonal antibody highly effective in reducing intravascular hemolysis in patients with paroxysmal nocturnal hemoglobinuria. It specifically binds to the terminal complement protein C5, inhibits its cleavage into C5a and C5b, and prevents the formations of the cytolytic complement pore (PubMed:24521109). The disease is caused by variants affecting the gene represented in this entry. An association study of C5 haplotypes and genotypes in individuals with chronic hepatitis C virus infection shows that individuals homozygous for the C5_1 haplotype have a significantly higher stage of liver fibrosis than individuals carrying at least 1 other allele. C5 mutation db Complement C5 entry