Everything about Factor Xi totally explained
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| Name = Coagulation factor XI (plasma thromboplastin antecedent)
| HGNCid = 3529
| Symbol = F11
| AltSymbols =; FXI; MGC141891
| OMIM = 264900
| ECnumber =
| Homologene = 86654
| MGIid = 99481
| GeneAtlas_image1 = PBB_GE_F11_206610_s_at_tn.png
| Function =
| Component =
| Process =
| Orthologs =
}}
Factor XI or
plasma thromboplastin antecedent is one of the
enzymes of the
coagulation cascade. Like many other coagulation factors, it's a
serine protease.
Physiology
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 it's also
autocatalytic, and FXI is a member of the "contact pathway" due to activation by FXIIa (with 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).
Protein structure and molecular biology
Although synthesized as a single polypeptide chain, FXI circulates as a homo-dimer. Every chain has a relative molecular mass of approximately 80000. Typical plasma concentrations of FXI are 5 mg/l, corresponding to a plasma concentration (of FXI dimers) of approximately 30nM.
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
Haemophilia C; this mainly occurs in
Ashkenazi Jews and is believed to affect approximately 8% of that population, of both sexes. 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's uncertain what determines these levels and how serious the procoagulant state is.
Further Information
Get more info on 'Factor Xi'.
|
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