Complement factor I inactivates surface-bound C3b

Stable Identifier
Reaction [transition]
Gallus gallus
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Complement factor I (CFI) is a serine protease that inhibits all complement pathways by degrading surface-bound C3b and C4b into inactive fragments. Factor I binds to CFH:C3b complex and cleaves C3b, producing iC3b which remains bound to the membrane. iC3b is proteolytically inactive and cannot contribute to the complement cascade process, though it does contribute to opsonization [Ross JD et al 1982; Masaki T et al 1992; Fukui A et al 2002; Nilsson SC et al 2010].

Predicted chicken CFI shows 51% amino acid sequence identity with its human counterpart. The chicken events of complement factor I activity have not been verified experimentally but are inferred from the orthologous human events.

Literature References
PubMed ID Title Journal Year
12417021 Mapping of the sites responsible for factor I-cofactor activity for cleavage of C3b and C4b on human C4b-binding protein (C4bp) by deletion mutagenesis

Fukui, A, Yuasa-Nakagawa, T, Murakami, Y, Funami, K, Kishi, N, Matsuda, T, Fujita, T, Seya, T, Nagasawa, S

J. Biochem. 2002
1386357 Factor I-dependent inactivation of human complement C4b of the classical pathway by C3b/C4b receptor (CR1, CD35) and membrane cofactor protein (MCP, CD46)

Masaki, T, Matsumoto, M, Nakanishi, I, Yasuda, R, Seya, T

J Biochem 1992
6214588 Generation of three different fragments of bound C3 with purified factor I or serum. I. Requirements for factor H vs CR1 cofactor activity

Ross, GD, Lambris, JD, Cain, JA, Newman, SL

J Immunol 1982
20044478 Analysis of binding sites on complement factor I that are required for its activity

Nilsson, SC, Nita, I, MÃ¥nsson, L, Groeneveld, TW, Trouw, LA, Villoutreix, BO, Blom, AM

J. Biol. Chem. 2010
Participant Of
Catalyst Activity
Catalyst Activity
serine-type endopeptidase activity of CFI [extracellular region]
Physical Entity
Inferred From
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