BIOL 1103 Lecture Notes - Cd59, Complement Component 5A, Complement Membrane Attack Complex
30 Jan 2013
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Complement: overall principles of complement, two overall phases: enzymatic and lytic (pore forming, split products are formed during complement cascade, both products are biologically active, there are three ways to activate c", and all converge at c3. There are three ways to activate c": classical pathway. Activated by c1 binding to igm or igg which are bound to ag. Specifically, c1q portion binds two fc regions, then c1r/c1s cleaves c4. C4b reacts fast, e. g. covalently binds bacterial cell surface whereas c4a. C4b binds c2, c1s cleaves c2, results in c4b2a complex (the c3 remains soluble convertase: mannose binding lectin, alternative pathway. Mbl is homologous to c1, but does not require antibody to activate. Like c1, mbl cleaves c2 and c4 to create the c3 convertase. C3 can tickover , i. e. spontaneously covalently bind surfaces. In appropriate environment, c3 complexes with b; b is cleaved by d. C3bbb complex recruits properdin (p); this is a c3 convertase.
