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. Author manuscript; available in PMC: 2021 Mar 1.
Published in final edited form as: Adv Chronic Kidney Dis. 2020 Mar;27(2):86–94. doi: 10.1053/j.ackd.2019.10.003

Figure 2. Inhibition of C3 convertases.

Figure 2.

The C3 convertases are inactivated by two mechanisms: decay acceleration and factor I mediated cleavage. Decay acceleration shortens the half-life of the convertase. Once the components are separated they cannot recombine. Factor I cleaves C3b and C4b, generating the catalytically inactive iC3b and iC4b fragments, respectively. Factor I requires the presence of proteins that can act as “cofactors”. CD46 (also called membrane cofactor protein, or MCP) and complement receptor-1 (CR1) can serve as cofactors for cleavage of either C3b or C4b. Factor H is a decay accelerator and a cofactor for the alternative pathway. C4 binding protein (C4bp) is a decay accelerator and cofactor for the classical and lectin pathway convertases.