C3 (complement)

C3 (complement)

The complement system, with the central role of C3 highlighted.

The C3 (complement) is a protein of the immune system that plays a central role in the complement system and contributes to innate immunity. As a part of the immune system, C3 plays a crucial role in the immune response and inflammation.

Structure

C3 is a large protein, consisting of an alpha and beta chain, which are linked by a disulfide bond. The alpha chain contains the C3 convertase binding site, while the beta chain contains a thioester bond, which is critical for the protein's function.

Function

C3 is involved in the activation of the complement system, including both the classical and alternative pathways. It is cleaved by C3 convertase into two fragments: C3a and C3b. C3a is an anaphylatoxin, which induces inflammation, while C3b binds to pathogens, marking them for destruction by phagocytes.

Clinical significance

Abnormalities in C3 can lead to diseases such as C3 deficiency and atypical hemolytic uremic syndrome (aHUS). C3 deficiency is a rare genetic disorder characterized by recurrent and severe bacterial infections. aHUS is a disease characterized by the formation of blood clots in small blood vessels throughout the body, which can lead to kidney failure.

See also

• Complement system
• Immune system
• C3 deficiency
• Atypical hemolytic uremic syndrome (aHUS)