Complement component 5
- OMIM: 120900
- UniProt: P01031
Complement component C5 is a protein of the complement system and has, as part of the membrane attack complex to the immune system of humans and animals an important function. Mutations in the C5 gene is responsible for an uncommon inherited immunodeficiency.
Structurally, the protein is related to alpha-2 -macroglobulin.
Genetics and construction
The gene encoding C5 C5 gene is located in humans on chromosome 9 locus q34.1. It consists of 41 exons and occupies a total of 79,000 base pairs.
The gene consists of 1676 amino acids in humans. The enzyme C5 convertase cleaves C5 into C5a, the two components (74 amino acid ) and the significantly larger C5b.
C5a is when people from 74 amino acids and has a molecular mass of 11 kDa. The polypeptide belongs to the group of anaphylatoxins and plays a major role in chemotaxis. In the blood serum B of C5a is cleaved, the terminal amino acid arginine by the enzyme carboxypeptidase, which " C5a des Arg " is created. The activity is thus only slightly reduced. C5a has a number of local and systemic effects. So it contracted for example, Smooth muscle, which can lead to bronchospasm. Furthermore, it increases the permeability of the blood capillaries. In mast cells, it releases histamine. C5a activates neutrophils and macrophages.
C5a can referred to two different receptors, C5aR and C5L2, bind, which are located on the surface of phagocytes. C5aR activates the G- protein -mediated signaling through the mitogen-activated protein kinase pathway. Inhibition of C5aR has potent anti-inflammatory effects. The function of C5L2 currently there is no consensus. The results of various working groups are very contradictory.
Since C5a, tumor growth is positively affected in an animal model mouse, inhibition of C5a is a potential target in cancer immunotherapy.
C5b has a molar mass of 190 kDa. It is deposited in the cell membrane of the target cell and constituting the first component of the membrane attack complex. Together with the components located thereon anlagernden C6, C7, C8 and C9, as a pore diameter of about 10 nm is formed in the cell membrane, leading to cytolysis of the cell.