C4b2akonvertaasia

C4b2akonvertaasia, also known as the classical pathway C3 convertase, is a crucial enzyme complex in the complement system of the immune response. It is formed during the activation of the classical pathway, which is typically triggered by the binding of antibodies to antigens. The C4b2a complex is responsible for cleaving the C3 protein, initiating a cascade of further complement activation.

The formation of C4b2a involves several steps. First, the C1 complex, activated by antigen-antibody complexes, cleaves C4 and C2. This cleavage generates C4b and C2b fragments. The C4b fragment then binds to the surface of the activating cell or particle. Subsequently, C2b binds to C4b, forming the C4b2a complex. This complex is a serine protease enzyme.

Once formed, C4b2a acts on C3, cleaving it into C3a and C3b fragments. The C3b fragment can then covalently bind to the target surface, promoting opsonization (marking the target for phagocytosis) and contributing to the formation of the next component of the complement cascade, the C5 convertase. The C3a fragment acts as an anaphylatoxin, contributing to inflammation. The activity of C4b2a is tightly regulated to prevent damage to host tissues.