Complement factor I
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| Complement Factor I
| |
| Identifiers | |
| Symbol | CFI |
| Alt. Symbols | C3b-INA, FI, IF, KAF, factor I |
| Entrez | 3426 |
| HUGO | 5394 |
| OMIM | 217030 |
| RefSeq | NM_000204 |
| UniProt | P05156 |
| Other data | |
| EC number | 3.4.21.45 |
| Locus | Chr. 4 q25 |
Complement Factor I (fI) is a protein of the Complement system, first isolated in 1966 in guinea pig serum[1] that regulates complement activation by cleaving cell-bound or fluid phase C3b and C4b.[2]
Contents |
Pathology
Factor I deficiency in turn leads to low levels of complement component 3 (C3) in plasma, due to unregulated activation of the complement alternative pathway, and it has been associated with recurrent bacterial infections in children; more recently, mutations in the Factor I gene have been shown to be implicated [3] in development of Haemolytic Uremic Syndrome, a renal disease also caused by unregulated complement activation.
Production
The gene for Factor I in humans is located on chromosome 4 [4] Factor I is synthesised mostly in the liver, and is initially secreted as a single 88 kDalton gene product; this precursor protein is then cleaved by furin to yield the mature fI protein, which is a disulphide-linked dimer of heavy chain (residues 19-335, 51 kDalton) and light chain (residues 340-583, 37 kDalton). Only the mature protein is active.
Structure
Both heavy and light chains bear Asn-linked glycans, on three distinct glycosylation sites each.
The fI heavy chain has four domains: a FIMAC domain, a Scavenger Receptor Cysteine Rich (SRCR) domain and two LDL-receptor Class A domains; the precise biological function of the heavy chain is not known, but it is likely to play a key role in recognising the fI cleavage substrates (C3b and C4b) and the cofactor proteins needed for cleavage of C3b (Factor H, CR1, MCP) and C4b (C4BP). The LDL-receptor domains are likely to contain one Calcium-binding site each.
The fI light chain is the serine protease domain containing the catalytic triad responsible for specific cleavage of C3b and C4b.
Genetic polymorphism in Factor I has been observed.[5]
References
- ↑ Nelson R, Jensen J, Gigli I, Tamura N (1966). "Methods for the separation, purification and measurement of nine components of hemolytic complement in guinea-pig serum". Immunochemistry 3 (2): 111-35. PMID 5960883.
- ↑ Lachmann P, Müller-Eberhard H (1968). "The demonstration in human serum of "conglutinogen-activating factor" and its effect on the third component of complement". J Immunol 100 (4): 691-8. PMID 5645214.
- ↑ Saunders R, Abarrategui-Garrido C, Frémeaux-Bacchi V, Goicoechea de Jorge E, Goodship T, López Trascasa M, Noris M, Ponce Castro I, Remuzzi G, Rodríguez de Córdoba S, Sánchez-Corral P, Skerka C, Zipfel P, Perkins S (2007). "The interactive Factor H-atypical hemolytic uremic syndrome mutation database and website: update and integration of membrane cofactor protein and Factor I mutations with structural models". Hum Mutat 28 (3): 222-34. PMID 17089378.
- ↑ Goldberger G, Bruns G, Rits M, Edge M, Kwiatkowski D (1987). "Human complement factor I: analysis of cDNA-derived primary structure and assignment of its gene to chromosome 4.". J Biol Chem 262 (21): 10065-71. PMID 2956252.
- ↑ Nakamura S, Abe K (1985). "Genetic polymorphism of human factor I (C3b inactivator)". Hum Genet 71 (1): 45-8. PMID 3897024.
Proteins: complement system (C, L, A) | |
|---|---|
| Activators | CLA: C3-convertase - MAC (C6, C7, C8, C9) - L: Mannan-binding lectin - A: Factor P/Properdin |
| Enzymes | C: C1Q/C1R/C1S - C4 - C2 - CLA: C3 - C5 (C5a) - L: MASP1 - MASP2 - A: Factor B - Factor D |
| Inhibitors | CLA: C1-inhibitor - Decay accelerating factor - Factor I - CL: C4BP - A: Factor H |
| Complement receptors | CR1 - CR2 - CR3 - CR4 - CD11b/CD11c/CD18 - Anaphylatoxin (C3a, C5a) |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
