The C5 gene (C5 stands for "Complement C5") is a protein coding gene located at chromosome 9q33.2. Alternative splicing results in multiple transcript variants.
The C5 gene encodes with the C5 component of the complement system, a complement component that plays an important role in inflammation and defense against pathogens.
The complex C5 protein consists of the C5-alpha and -beta chains connected by a disulfide bridge. Activation of C5 by a C5 convertase initiates the spontaneous assembly of the late complement components, C5-C9, into the membrane attack complex (MAC).
C5b has a transient binding site for C6. The C5b-C6 complex is the basis for the assembly of the lytic complex.
C5a anaphylatoxin, derived from proteolytic degradation of complement C5, is a mediator of the local inflammatory process. Binding to the receptor C5AR1 triggers a number of responses, including release of intracellular calcium, smooth muscle contraction, increased vascular permeability, and release of histamine from mast cells and basophilic leukocytes. C5a is also a potent chemokine that stimulates the locomotion of polymorphonuclear leukocytes and directs their migration to sites of inflammation.
Mutations in the C5 gene cause complement component 5 deficiency (C5 deficiency syndrome), a chronic disease characterized by recurrent bacterial infections.