Factor XI

Coagulation factor XI
PDB rendering based on 1xx9.
Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 1XX9, 1XXD, 1XXF, 1ZHM, 1ZHP, 1ZHR, 1ZJD, 1ZLR, 1ZMJ, 1ZML, 1ZMN, 1ZOM, 1ZPB, 1ZPC, 1ZPZ, 1ZRK, 1ZSJ, 1ZSK, 1ZSL, 1ZTJ, 1ZTK, 1ZTL, 2F83, 2FDA, 2J8J, 2J8L, 3BG8, 3SOR, 3SOS, 4CR5, 4CR9, 4CRA, 4CRB, 4CRC, 4CRD, 4CRE, 4CRF, 4CRG, 4NA7, 4NA8, 4TY6, 4TY7, 4WXI, 4X6M, 4X6N, 4X6O, 4X6P
Identifiers
Symbols	F11 ; FXI
External IDs	OMIM: 264900 MGI: 99481 HomoloGene: 86654 ChEMBL: 2820 GeneCards: F11 Gene
EC number	3.4.21.27
Gene ontology Molecular function • serine-type endopeptidase activity • protein binding • heparin binding Cellular component • extracellular region • extracellular space • plasma membrane • membrane • extracellular exosome Biological process • blood coagulation • blood coagulation, intrinsic pathway • plasminogen activation • positive regulation of fibrinolysis Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	2160	109821
Ensembl	ENSG00000088926	ENSMUSG00000031645
UniProt	P03951	Q91Y47
RefSeq (mRNA)	NM_000128	NM_028066
RefSeq (protein)	NP_000119	NP_082342
Location (UCSC)	Chr 4: 186.27 – 186.29 Mb	Chr 8: 45.24 – 45.26 Mb
PubMed search	[1]	[2]

Factor XI or plasma thromboplastin antecedent is the zymogen form of factor XIa, one of the enzymes of the coagulation cascade. Like many other coagulation factors, it is a serine protease. In humans, Factor XI is encoded by the F11 gene.

Function

Factor XI (FXI) is produced by the liver and circulates as a homo-dimer in its inactive form. The plasma half-life of FXI is approximately 52 hours. The zymogen factor is activated into factor XIa by factor XIIa (FXIIa), thrombin, and FXIa itself; due to its activation by FXIIa, FXI is a member of the "contact pathway" (which includes HMWK, prekallikrein, factor XII, factor XI, and factor IX).

Factor XIa activates factor IX by selectively cleaving arg-ala and arg-val peptide bonds. Factor IXa, in turn, activates factor X.

Inhibitors of factor XIa include protein Z-dependent protease inhibitor (ZPI, a member of the serine protease inhibitor/serpin class of proteins), which is independent of protein Z (its action on factor X, however, is protein Z-dependent, hence its name).

Structure

Although synthesized as a single polypeptide chain, FXI circulates as a homodimer. Every chain has a relative molecular mass of approximately 80000. Typical plasma concentrations of FXI are 5 μg/mL, corresponding to a plasma concentration (of FXI dimers) of approximately 30 nM. The FXI gene is 23kb in length, has 15 exons, and is found on chromosome 4q32-35.

Role in disease

Deficiency of factor XI causes the rare hemophilia C; this mainly occurs in Ashkenazi Jews and is believed to affect approximately 8% of that population. Less commonly, hemophilia C can be found in Jews of Iraqi ancestry and in Israeli Arabs. The condition has been described in other populations at around 1% of cases. It is an autosomal recessive disorder. There is little spontaneous bleeding, but surgical procedures may cause excessive blood loss, and prophylaxis is required.

Low levels of factor XI also occur in many other disease states, including Noonan syndrome.

High levels of factor XI have been implicated in thrombosis, although it is uncertain what determines these levels and how serious the procoagulant state is.

See also

• Contact activation pathway (also known as the intrinsic pathway)
• Tissue factor pathway (also known as the extrinsic pathway)

External links

• The MEROPS online database for peptidases and their inhibitors: S01.213