Complement factor B (CFB)
The protein contains 764 amino acids for an estimated molecular weight of 85533 Da.
Factor B which is part of the alternate pathway of the complement system is cleaved by factor D into 2 fragments: Ba and Bb. Bb, a serine protease, then combines with complement factor 3b to generate the C3 or C5 convertase. It has also been implicated in proliferation and differentiation of preactivated B-lymphocytes, rapid spreading of peripheral blood monocytes, stimulation of lymphocyte blastogenesis and lysis of erythrocytes. Ba inhibits the proliferation of preactivated B-lymphocytes. (updated: Sept. 12, 2018)
Protein identification was indicated in the following studies:
Methods
The following articles were analysed to gather the proteome content of erythrocytes.
The gene or protein list provided in the studies were processed using the ID mapping API of Uniprot in September 2018. The number of proteins identified and mapped without ambiguity in these studies is indicated below.
Only Swiss-Prot entries (reviewed) were considered for protein evidence assignation.
| Publication | Identification 1 | Uniprot mapping 2 | Not mapped / Obsolete | TrEMBL | Swiss-Prot |
|---|---|---|---|---|---|
| Goodman (2013) | 2289 (gene list) | 2278 | 53 | 20599 | 2269 |
| Lange (2014) | 1234 | 1234 | 7 | 28 | 1224 |
| Hegedus (2015) | 2638 | 2622 | 0 | 235 | 2387 |
| Wilson (2016) | 1658 | 1528 | 170 | 291 | 1068 |
| d'Alessandro (2017) | 1826 | 1817 | 2 | 0 | 1815 |
| Bryk (2017) | 2090 | 2060 | 10 | 108 | 1942 |
| Chu (2018) | 1853 | 1804 | 55 | 362 | 1387 |
1 as available in the article and/or in supplementary material
2 uniprot mapping returns all protein isoforms as one entry
The compilation of older studies can be retrieved from the Red Blood Cell Collection database.
The data and differentiation stages presented below come from the proteomic study and analysis performed by our partners of the GReX consortium, more details are available in their published work.
This protein is annotated as membranous in Gene Ontology.
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Biological Process
Complement activation
Complement activation, alternative pathway
Regulation of complement activation
The reference OMIM entry for this protein is 138470
Complement factor b; cfb
Factor b; fb
Properdin factor b; bf
Factor b, properdin
C3 proactivator
C3 proaccelerator
Glycine-rich beta-glycoprotein; gbg
DESCRIPTION
The CFB gene encodes complement factor B, which is part of the alternative complement pathway. Complement factor B is cleaved into a 30-kD N terminal 'Ba' fragment and a 57-kD C-terminal 'Bb' fragment by factor D (CFD; 134350) in the presence of C3b. The C-terminal half of the Bb fragment contains the essential active site residues characteristic of serine proteases, but has a molecular weight twice that of proteinases previously described, suggesting that it is a novel type of serine proteinase. The Bb fragment forms the C3bBb alternative pathway convertase (Christie and Gagnon, 1983). Complement factor B was originally known as a glycine-rich beta-glycoprotein (GBG).CLONING
Christie and Gagnon (1983) determined that the major product of factor B cleavage, Bb, is composed of 505 amino acids and has a molecular mass of 57 kD. Campbell and Porter (1983) isolated clones corresponding to the complement protein factor B gene from a human liver cDNA library.BIOCHEMICAL FEATURES
- Crystal Structure Forneris et al. (2010) presented crystal structures of the proconvertase C3bB (see 120700) at 4-angstrom resolution and its complex with factor D (134350) at 3.5-angstrom resolution. Their data showed how factor B binding to C3b forms an open 'activation' state of C3bB. Factor D specifically binds the open conformation of factor B through a site distant from the catalytic center and is activated by the substrate, which displaces factor D's self-inhibitory loop. This concerted proteolytic mechanism, which if cofactor-dependent and substrate-induced, restricts complement amplification to C3b-tagged target cells.GENE STRUCTURE
Campbell and Porter (1983) determined that the Bb portion of the factor B gene is about 4 kb long. The 3-prime end of the gene codes for amino acids 87-505 of Bb and includes the serine protease domain of the protein. Campbell (1987) determined that the complete factor B gene spans 6 kb and contains 18 exons, whereas the C2 gene (613927) spans 18 kb.MAPPING
Allen (1974) showed that GBG and HLA (see, e.g., HLA-A; 142800) are tightly linked on chromosome 6p21. No recombinants were observed among 44 children from 12 informative families. Rittner et al. (1975) found a recombination fraction of 6.1% between HLA and the GBG locus, which they symbolized 'Bf.' They further proposed that Bf is closely linked to the MLC locus with the following order: HLA (first locus)--HLA (second locus)--MLC--Bf--PGM3 (172100). Teisberg et al. (1975) found 90 apparently nonrecombinant offspring from 23 matings. Raum et al. (1976) concluded that the factor B locus and the C2 deficiency locus (217000) are close together, and that the 2 loci are 3 to 5 cM from the HLA-A and HLA-B loci. Two crossovers out of 57 were observed for C2 versus HLA-B, and 3 out of 72 for factor B versus HLA-B. The order of the genes was taken to be HLA-A, -B, -D, factor B, C2. Albert et al. (1975) presented data they interpreted as suggesting that the Bf locus is between HLA-B and HLA-D. Linkage disequilibrium likewise suggested that Bf is close to HLA-B but not close to HLA-A (Bender et al., 1977). Analysis of what Edwards preferred to call allelic association (because it does not have implications of a disturbance driven by selection or other forces as may 'linkage disequilibrium') led Arnason et al. (1977) to conclude that the HLA-B locus and the Bf locus are very close. For most workers, linkage disequilib ... More on the omim web site
Nov. 17, 2018: Protein entry updated
Automatic update: OMIM entry 138470 was added.
Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).