Complement component 5

Complement component 5 (C5) is a protein that is part of the complement system, a complex system of proteins that play a crucial role in the immune system and inflammation. C5 is produced by the liver and is found in the blood plasma. It is involved in a variety of immune responses, including the promotion of inflammation, the attraction of white blood cells to sites of infection, and the destruction of bacteria and other foreign substances.

Structure

C5 is a large protein composed of multiple subunits. It is made up of a heavy chain and a light chain, which are linked together by disulfide bonds. The heavy chain contains a region known as the C5 convertase binding site, which is crucial for the activation of C5.

Function

The primary function of C5 is to initiate the formation of the Membrane Attack Complex (MAC), a group of proteins that form a pore in the membrane of invading pathogens, leading to their destruction. This process is known as complement activation.

C5 is also involved in the process of chemotaxis, the attraction of white blood cells to sites of infection. It does this by being cleaved into two smaller fragments, C5a and C5b. C5a is a potent chemotactic factor, meaning it can attract white blood cells to the site of infection. C5b, on the other hand, is involved in the formation of the MAC.

Clinical significance

Mutations in the C5 gene can lead to a variety of health problems. For example, a deficiency in C5 can result in an increased susceptibility to certain types of bacterial infections. On the other hand, overactivity of C5 has been implicated in a number of inflammatory diseases, including rheumatoid arthritis, lupus, and asthma.

There are also drugs that target C5, such as eculizumab, which is used to treat conditions like paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome.

See also

• Complement system
• Membrane Attack Complex
• Complement activation
• Chemotaxis