About Complement Component:
Complement Component Mechanism
Complement components can be activated via three pathways: classical, alternative, and lectin. The classical pathway is set in motion when C1q is attached to antibodies connected to antigen, activating C1r and C1s, which cleave C2 and C4.
The lectin pathway is triggered when this component encounters conserved carbohydrate motifs which are pathogenic. This activates the serine proteases associated with MBL (MASPs), cleaving C2 and C4. C2 and C4 cleavage products form the lectin and classical path C3 convertase, C4bC2a, which converts C3 into C3b and C3a.
The alternative pathway (AP) is activated when C3 hydrolyzes spontaneously to form C3(H2O)Bb, in the presence of Factors B and D, which in turn leads to the gradual formation of the AP C3 convertase (C3bBb) and AP C5 convertase.
Complement Component Interactions
Complement component C3 is a multifunctional protein that interacts with many different ligands and receptors.
Complement component 3 has been shown to interact with Factor H.
C5a interacts with receptor protein C5aR (CD88) on the surface of target cells such as neutrophils, macrophages, and endothelial cells.
Complement Component Function
The primary function of complement proteins is to help destroy pathogens through cell lysis or opsonization.
The C3 protein is essential for activating the complement system. Foreign invaders in the body trigger the C3 protein to be cleaved into two smaller pieces. C3b, one of these pieces, interacts with other proteins on the cells' surface to trigger the complement system's response.
Complement Component Structure
C2 has 39% identity with protein Factor B. Human C2 is produced as an inactive zymogen consisting of five domains.
Crystallographic C3 structures reveal that this protein contains 13 domains.