Complement factor B

CFB
Identifiers
Aliases	CFB, Cfb, AI195813, AI255840, Bf, C2, Fb, H2-Bf, AHUS4, ARMD14, BFD, CFAB, CFBD, FBI12, GBG, PBF2, complement factor B
External IDs	OMIM: 138470; MGI: 105975; GeneCards: CFB
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 3HS0, 1DLE, 1Q0P, 1RRK, 1RS0, 1RTK, 2OK5, 2WIN, 2XWB, 2XWJ, 3HRZ
Enzyme activity EC # BRENDA ExPASy KEGG MetaCyc 3.4.21.47 ↗ ↗ ↗ ↗
Gene location (Human) Chr. Chromosome 6 (human) Band 6p21.33 Start 31,945,650 bp End 31,952,084 bp
Gene location (Mouse) Chr. Chromosome 17 (mouse) Band 17 B1|17 18.41 cM Start 35,075,350 bp End 35,081,494 bp
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in right lobe of liver gallbladder appendix duodenum islet of Langerhans olfactory zone of nasal mucosa Descending thoracic aorta gastric mucosa right coronary artery human kidney Top expressed in proximal tubule right kidney human kidney white adipose tissue hepatobiliary system liver jejunum ileum colon duodenum More reference expression data BioGPS More reference expression data
Gene ontology Molecular function peptidase activity serine-type peptidase activity serine-type endopeptidase activity hydrolase activity complement binding protein binding Cellular component extracellular region plasma membrane blood microparticle extracellular exosome extracellular space Biological process complement activation regulation of complement activation proteolysis immune system process complement activation, alternative pathway innate immune response Sources:Amigo / QuickGO
Orthologs Databases NCBI: entry; OMA: entry Species Human Mouse Entrez 629 14962 Ensembl ENSG00000243570 ENSG00000239754 ENSG00000243649 ENSG00000241253 ENSG00000242335 ENSG00000241534 ENSG00000204359 ENSMUSG00000090231 UniProt P00751 P04186 RefSeq (mRNA) NM_001710 NM_001142706 NM_008198 RefSeq (protein) NP_001701 NP_001136178 NP_032224 NP_001389804 Location (UCSC) Chr 6: 31.95 – 31.95 Mb Chr 17: 35.08 – 35.08 Mb PubMed search
Wikidata
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Complement factor B is a protein that in humans is encoded by the CFB gene.

Function

This gene encodes complement factor B, a component of the alternative pathway of complement activation. It is directly paralogous to complement component 2 (C2) of the classical pathway, occupying the same locus on Chromosome 6 (6p21.33) and sharing 39% sequence homology, with even greater functional homology due to conservative amino acid replacements accounting for 11% of the divergence. Both are serine proteases with directly analogous functions in their respective complement activation pathways.

Factor B circulates in the blood as a single chain polypeptide. Upon activation of the alternative pathway, it is cleaved by complement factor D yielding the noncatalytic chain Ba and the catalytic subunit Bb. The active subunit Bb harbors the serine protease domain that associates with C3b to form the alternative pathway C3 convertase. Bb is involved in the proliferation of preactivated B lymphocytes, while Ba inhibits their proliferation. This gene localizes to the major histocompatibility complex (MHC class III) region on chromosome 6. This cluster includes several genes involved in regulation of the immune reaction. The polyadenylation site of this gene is 421 bp from the 5' end of the gene for complement component 2.

Alternative pathway. (Some labels are in Polish.)

Complement tests

C4 (C)	FB (A)	C3	CH50	Conditions
·	↓	↓	↓	PSG, C3 NeF AA
↓	·	↓	·	HAE, C4D
·	·	·	↓	TCPD
↓	·/↓	↓	↓	SLE
↑	↑	↑	↑	inflammation

Further reading

• Ambrus JL, Peters MG, Fauci AS, Brown EJ (March 1990). "The Ba fragment of complement factor B inhibits human B lymphocyte proliferation". Journal of Immunology. 144 (5). Baltimore: 1549–1553. doi:10.4049/jimmunol.144.5.1549. PMID 2307833.
• Bradley DT, Zipfel PF, Hughes AE (June 2011). "Complement in age-related macular degeneration: a focus on function". Eye. 25 (6). London, England: 683–693. doi:10.1038/eye.2011.37. PMC 3178140. PMID 21394116.
• Campbell RD (January 1987). "The molecular genetics and polymorphism of C2 and factor B". British Medical Bulletin. 43 (1): 37–49. doi:10.1093/oxfordjournals.bmb.a072175. PMID 3315100.
• Campbell RD, Bentley DR, Morley BJ (September 1984). "The factor B and C2 genes". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 306 (1129): 367–378. Bibcode:1984RSPTB.306..367C. doi:10.1098/rstb.1984.0097. PMID 6149579.
• Yu CY (1999). "Molecular genetics of the human MHC complement gene cluster". Experimental and Clinical Immunogenetics. 15 (4): 213–230. doi:10.1159/000019075. PMID 10072631. S2CID 25061446.
• Rawal N, Pangburn MK (March 2001). "Structure/function of C5 convertases of complement". International Immunopharmacology. 1 (3): 415–422. doi:10.1016/S1567-5769(00)00039-4. PMID 11367526.
• Arnason A, Larsen B, Marshall WH, Edwards JH, Macintosh P, Olaisen B, et al. (August 1977). "Very close linkage between HLA-B and Bf inferred from allelic association". Nature. 268 (5620): 527–528. Bibcode:1977Natur.268..527A. doi:10.1038/268527a0. PMID 889587. S2CID 4262433.
• Barnum SR, Ishii Y, Agrawal A, Volanakis JE (October 1992). "Production and interferon-gamma-mediated regulation of complement component C2 and factors B and D by the astroglioma cell line U105-MG". The Biochemical Journal. 287. 287 ( Pt 2) (2): 595–601. doi:10.1042/bj2870595. PMC 1133207. PMID 1445220.
• Yancey KB, Overholser O, Domloge-Hultsch N, Li LJ, Caughman SW, Bisalbutra P (March 1992). "Human keratinocytes and A-431 cells synthesize and secrete factor B, the major zymogen protease of the alternative complement pathway". The Journal of Investigative Dermatology. 98 (3): 379–383. doi:10.1111/1523-1747.ep12499812. PMID 1545147.
• Niemann MA, Bhown AS, Miller EJ (March 1991). "The principal site of glycation of human complement factor B". The Biochemical Journal. 274. 274 ( Pt 2) (2): 473–480. doi:10.1042/bj2740473. PMC 1150163. PMID 2006911.
• Davrinche C, Abbal M, Clerc A (1991). "Molecular characterization of human complement factor B subtypes". Immunogenetics. 32 (5): 309–312. doi:10.1007/bf00211644. PMID 2249879. S2CID 13698345.
• Farries TC, Lachmann PJ, Harrison RA (August 1988). "Analysis of the interaction between properdin and factor B, components of the alternative-pathway C3 convertase of complement". The Biochemical Journal. 253 (3): 667–675. doi:10.1042/bj2530667. PMC 1149358. PMID 3140783.
• Wu LC, Morley BJ, Campbell RD (January 1987). "Cell-specific expression of the human complement protein factor B gene: evidence for the role of two distinct 5'-flanking elements". Cell. 48 (2): 331–342. doi:10.1016/0092-8674(87)90436-3. PMID 3643061. S2CID 32752642.
• Campbell RD, Porter RR (July 1983). "Molecular cloning and characterization of the gene coding for human complement protein factor B". Proceedings of the National Academy of Sciences of the United States of America. 80 (14): 4464–4468. Bibcode:1983PNAS...80.4464C. doi:10.1073/pnas.80.14.4464. PMC 384059. PMID 6308626.
• Morley BJ, Campbell RD (January 1984). "Internal homologies of the Ba fragment from human complement component Factor B, a class III MHC antigen". The EMBO Journal. 3 (1): 153–157. doi:10.1002/j.1460-2075.1984.tb01776.x. PMC 557312. PMID 6323161.
• Christie DL, Gagnon J (January 1983). "Amino acid sequence of the Bb fragment from complement Factor B. Sequence of the major cyanogen bromide-cleavage peptide (CB-II) and completion of the sequence of the Bb fragment". The Biochemical Journal. 209 (1): 61–70. doi:10.1042/bj2090061. PMC 1154056. PMID 6342610.
• Mole JE, Anderson JK, Davison EA, Woods DE (March 1984). "Complete primary structure for the zymogen of human complement factor B". The Journal of Biological Chemistry. 259 (6): 3407–3412. doi:10.1016/S0021-9258(17)43108-5. PMID 6546754.
• Woods DE, Markham AF, Ricker AT, Goldberger G, Colten HR (September 1982). "Isolation of cDNA clones for the human complement protein factor B, a class III major histocompatibility complex gene product". Proceedings of the National Academy of Sciences of the United States of America. 79 (18): 5661–5665. Bibcode:1982PNAS...79.5661W. doi:10.1073/pnas.79.18.5661. PMC 346964. PMID 6957884.
• Maruyama K, Sugano S (January 1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene. 138 (1–2): 171–174. doi:10.1016/0378-1119(94)90802-8. PMID 8125298.
• Mejía JE, Jahn I, de la Salle H, Hauptmann G (January 1994). "Human factor B. Complete cDNA sequence of the BF*S allele". Human Immunology. 39 (1): 49–53. doi:10.1016/0198-8859(94)90100-7. PMID 8181962.

External links

• GeneReviews/NCBI/NIH/UW entry on Atypical Hemolytic-Uremic Syndrome
• OMIM entries on Atypical Hemolytic-Uremic Syndrome
• The MEROPS online database for peptidases and their inhibitors: S01.196
• Complement+Factor+B at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• Overview of all the structural information available in the PDB for UniProt: P00751 (Complement factor B) at the PDBe-KB.