Question

Can someone help me with complement proteins? I know there's 3 parts that is alternative, lectin and classical but I don't seem to understand the flow of it.

Answer 1

ANSWER :

COMPLEMENT PROTEINS : Complement proteins are those plasma proteins which activates by pathogens or indirectly by antibody, which occurs to cascade reactions, generates active components with different functions.

PARTS OF COMPLEMENT PROTEINS :

1. CLASSICAL PATHWAY : It is triggered by C1 complex activation. C1 is composed of 1 molecule of C1g, two molecules of C1r and C1s. C1g binds to IgM antigens. C1g binds to pathogen surfaces which leads to changes in C1g molecule leading to activation of 2 C1r molecules. It is a serine protease which forms C1s serine protease. The component of C1r splits into C4, C2which produces C4a, C4b, C2a, C2b binds for forming of classical pathway

2. ALTERNATIVE PATHWAY : This pathway is continuously activated in a low level leading to hydrolysis of C3 due to thioester breakdown. This pathway does not depends on antibodies binding pathogens. C3b is generated by C3, when internal thioester reacts with hydroxyl of a moleculeon the surface of pathogen C3b binds to form C3bB. This process of D factor is cleaved to Ba Bb with C3b to form C3bBb which is a alternative processof C3 pathway.

3. LECTIN PATHWAY : This pathway is a homologous to classical. It is activated with binding of MBL to mannose on the surface of pathogen, which splits into C4 to C4a C4b and C2 to C2a C2b C4b C2b binds to form classical C3 convertase. Ficolins are the homologous which functions through MASP. The larger fragment of C2 named as C2a. Ficolins and their bindings compensate for the lack of specific pathogen recognize molecules.