View source for Factor XI

{{Short description|Mammalian protein found in Homo sapiens}}
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{{Infobox gene}}

'''Factor XI''', or '''plasma thromboplastin antecedent''', is the [[zymogen]] form of factor XIa, one of the [[enzyme]]s involved in [[coagulation]]. Like many other coagulation factors, it is a [[serine protease]].  In humans, factor XI is encoded by ''F11'' [[gene]].<ref name="Fujikawa_1986">{{cite journal | vauthors = Fujikawa K, Chung DW, Hendrickson LE, Davie EW | title = Amino acid sequence of human factor XI, a blood coagulation factor with four tandem repeats that are highly homologous with plasma prekallikrein | journal = Biochemistry | volume = 25 | issue = 9 | pages = 2417–2424 | date = May 1986 | pmid = 3636155 | doi = 10.1021/bi00357a018 }}</ref><ref name="Asakai_1987">{{cite journal | vauthors = Asakai R, Davie EW, Chung DW | title = Organization of the gene for human factor XI | journal = Biochemistry | volume = 26 | issue = 23 | pages = 7221–7228 | date = Nov 1987 | pmid = 2827746 | doi = 10.1021/bi00397a004 }}</ref><ref name="Kato_1989">{{cite journal | vauthors = Kato A, Asakai R, Davie EW, Aoki N | title = Factor XI gene (F11) is located on the distal end of the long arm of human chromosome 4 | journal = Cytogenetics and Cell Genetics | volume = 52 | issue = 1–2 | pages = 77–78 | year = 1989 | pmid = 2612218 | doi = 10.1159/000132844 }}</ref><ref name="Buetow_1991">{{cite journal | vauthors = Buetow KH, Shiang R, Yang P, Nakamura Y, Lathrop GM, White R, Wasmuth JJ, Wood S, Berdahl LD, Leysens NJ | title = A detailed multipoint map of human chromosome 4 provides evidence for linkage heterogeneity and position-specific recombination rates | journal = American Journal of Human Genetics | volume = 48 | issue = 5 | pages = 911–925 | date = May 1991 | pmid = 1673289 | pmc = 1683054 }}</ref>

== Function ==

Factor XI (FXI) is produced by the [[liver]] and circulates as a [[protein dimer|homo-dimer]] in its inactive form.<ref name="Wu_2008">{{cite journal | vauthors = Wu W, Sinha D, Shikov S, Yip CK, Walz T, Billings PC, Lear JD, Walsh PN | title = Factor XI homodimer structure is essential for normal proteolytic activation by factor XIIa, thrombin, and factor XIa | journal = The Journal of Biological Chemistry | volume = 283 | issue = 27 | pages = 18655–18664 | date = Jul 2008 | pmid = 18441012 | pmc = 2441546 | doi = 10.1074/jbc.M802275200 | doi-access = free }}</ref> The plasma half-life of FXI is approximately 52 hours. The zymogen factor is activated into ''factor XIa'' by [[factor XII]]a (FXIIa), [[thrombin]], and FXIa itself; due to its activation by FXIIa, FXI is a member of the "contact pathway" (which includes [[high molecular weight kininogen|HMWK]], [[prekallikrein]], [[factor XII]], factor XI, and [[factor IX]]).<ref name="Walsh_2001">{{cite journal | vauthors = Walsh PN | title = Roles of platelets and factor XI in the initiation of blood coagulation by thrombin | journal = Thrombosis and Haemostasis | volume = 86 | issue = 1 | pages = 75–82 | date = Jul 2001 | pmid = 11487044 | doi = 10.1055/s-0037-1616203 | s2cid = 32572142 | url = http://www.schattauer.de/index.php?id=1268&pii=th01070007&no_cache=1 | access-date = 2009-01-07 | archive-url = https://web.archive.org/web/20160416092638/http://www.schattauer.de/index.php?id=1268&pii=th01070007&no_cache=1 | archive-date = 2016-04-16 | url-status = dead | url-access = subscription }}</ref>

Factor XIa activates factor IX by selectively cleaving [[arginine|arg]]-[[alanine|ala]] and [[arginine|arg]]-[[valine|val]] [[peptide bond]]s. Factor IXa, in turn, forms a complex with Factor VIIIa (FIXa-FVIIIa) and activates [[factor X]].

Physiological 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.<ref name="Asakai_1987" /><ref name="Kato_1989" />

Factor XI consists of four [[PAN domain|apple domain]]s, that create a disk-like platform around the base of a fifth, catalytic [[serine protease]] domain.
One contains a binding site for [[thrombin]], another for [[high molecular weight kininogen]], a third one for [[factor IX]], [[heparin]] and [[glycoprotein Ib]] and the fourth is implicated in forming the factor XI homodimer, including a [[cysteine]] residue that creates a [[disulfide bond]].

In the homodimer, the apple domains create two disk-like platforms connected together at an angle, with the catalytic domains sticking out at each side of the dimer.

Activation by thrombin or [[factor XII]]a is achieved by cleavage of Arg369-Ile370 peptide bonds on both subunits of the dimer. This results in a partial detachment of the catalytic domain from the disk-like apple domains, still linked to the fourth domain with a disulfide bond, but now farther from the third domain.
This is thought that this exposes the factor IX binding site of the third apple domain, allowing factor XI's protease activity on it.
<ref>{{cite journal | vauthors = Emsley J, McEwan PA, Gailani D | title = Structure and function of factor XI | journal = Blood | volume = 115 | issue = 13 | pages = 2569–2577 | date = Apr 2010 | pmid = 20110423 | pmc = 4828079 | doi = 10.1182/blood-2009-09-199182 }}</ref>

== Role in disease ==

Deficiency of factor XI causes the rare [[hemophilia C]]; this mainly occurs in [[Ashkenazi]] [[Jew]]s 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. There is little spontaneous bleeding, but surgical procedures may cause excessive blood loss, and prophylaxis is required.<ref name="BoltonMaggs_1996">{{cite journal | vauthors = Bolton-Maggs PH | title = Factor XI deficiency | journal = Bailliere's Clinical Haematology | volume = 9 | issue = 2 | pages = 355–368 | date = Jun 1996 | pmid = 8800510 | doi = 10.1016/S0950-3536(96)80068-0 }}</ref>

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.

=== Inhibition ===
Pharmacological inhibitors of factor XI that are under clinical development but not yet approved for treatment {{as of|2022|05|lc=y}} include the oral factor XIa inhibitors [[Asundexian]] (BAY 2433334)<ref name="NCT04304508">{{ClinicalTrialsGov|NCT04304508|Study to Gather Information About Proper Dosing and Safety of the Oral FXIa Inhibitor BAY 2433334 in Patients Following a Recent Non Cardioembolic Ischemic Stroke Which Occurs When a Blood Clot Has Formed Somewhere in the Human Body (But Not in the Heart) Travelled to the Brain. (PACIFIC-STROKE)}}</ref> and [[Milvexian]]<ref name="Weitz_2021">{{cite journal | vauthors = Weitz JI, Strony J, Ageno W, Gailani D, Hylek EM, Lassen MR, Mahaffey KW, Notani RS, Roberts R, Segers A, Raskob GE | title = Milvexian for the Prevention of Venous Thromboembolism | journal = The New England Journal of Medicine | volume = 385 | issue = 23 | pages = 2161–2172 | date = November 2021 | pmid = 34780683 | pmc = 9540352 | doi = 10.1056/NEJMoa2113194 | s2cid = 244132392 }}</ref> as well as the monoclonal anti-factor XI antibody [[abelacimab]] (MAA868). The idea behind producing such an inhibitor is that XI is mostly involved in intrinsic/contact activation pathway,<ref name="Long_2016">{{cite journal | vauthors = Long AT, Kenne E, Jung R, Fuchs TA, Renné T | title = Contact system revisited: an interface between inflammation, coagulation, and innate immunity | journal = Journal of Thrombosis and Haemostasis | volume = 14 | issue = 3 | pages = 427–437 | date = March 2016 | pmid = 26707513 | doi = 10.1111/jth.13235 | doi-access = free }}</ref> which plays a bigger role in [[thrombosis]] as opposed to [[hemostasis]], so targeting it may reduce clotting risks without a corresponding increase in bleeding.<ref name="Verhamme_2021">{{cite journal | vauthors = Verhamme P, Yi BA, Segers A, Salter J, Bloomfield D, Buller HR, Raskob GE, Weitz JI | title = Abelacimab for Prevention of Venous Thromboembolism | journal = The New England Journal of Medicine | volume = 385 | issue = 7 | pages = 609–617 | date = 12 August 2021 | pmid = 34297496 | doi = 10.1056/NEJMoa2105872 | s2cid = 236198598 | doi-access = free }}</ref> An [[abelacimab]] trial appears to have indeed produced this result.<ref>{{cite journal | vauthors = Ruff CT, Patel SM, Giugliano RP, Morrow DA, Hug B, Kuder JF, Goodrich EL, Chen SA, Goodman SG, Joung B, Kiss RG, Spinar J, Wojakowski W, Weitz JI, Murphy SA, Wiviott SD, Parkar S, Bloomfield D, Sabatine MS | title = Abelacimab versus Rivaroxaban in Patients with Atrial Fibrillation | journal = The New England Journal of Medicine | volume = 392 | issue = 4 | pages = 361–371 | date = 23 January 2025 | pmid = 39842011 | doi = 10.1056/NEJMoa2406674 }}</ref>

== See also ==
*[[Contact activation pathway]] (also known as the ''intrinsic pathway'')
*[[Tissue factor pathway]] (also known as the ''extrinsic pathway'')

== References ==
{{Reflist|33em}}

== Further reading ==
{{Refbegin|33em}}
* {{cite journal | vauthors = Gailani D, Zivelin A, Sinha D, Walsh PN | title = Do platelets synthesize factor XI? | journal = Journal of Thrombosis and Haemostasis | volume = 2 | issue = 10 | pages = 1709–1712 | year = 2005 | pmid = 15456479 | doi = 10.1111/j.1538-7836.2004.00935.x | s2cid = 5962587 | doi-access = free }}
* {{cite journal | vauthors = Dossenbach-Glaninger A, Hopmeier P | title = Coagulation factor XI: a database of mutations and polymorphisms associated with factor XI deficiency | journal = Blood Coagulation & Fibrinolysis | volume = 16 | issue = 4 | pages = 231–238 | date = Jun 2005 | pmid = 15870541 | doi = 10.1097/01.mbc.0000169214.62560.a5 | s2cid = 23922781 }}
* {{cite journal | vauthors = Seligsohn U | title = Factor XI in haemostasis and thrombosis: past, present and future | journal = Thrombosis and Haemostasis | volume = 98 | issue = 1 | pages = 84–89 | date = Jul 2007 | pmid = 17597996 | doi = 10.1160/th07-04-0246 | doi-access = free }}
* {{cite journal | vauthors = Meijers JC, Davie EW, Chung DW | title = Expression of human blood coagulation factor XI: characterization of the defect in factor XI type III deficiency | journal = Blood | volume = 79 | issue = 6 | pages = 1435–1440 | date = Mar 1992 | pmid = 1547342 | doi = 10.1182/blood.V79.6.1435.1435 | doi-access = free }}
* {{cite journal | vauthors = Gailani D, Broze GJ | title = Factor XI activation in a revised model of blood coagulation | journal = Science | location = New York, N.Y. | volume = 253 | issue = 5022 | pages = 909–912 | date = Aug 1991 | pmid = 1652157 | doi = 10.1126/science.1652157 | bibcode = 1991Sci...253..909G | s2cid = 9262836 }}
* {{cite journal | vauthors = Buetow KH, Shiang R, Yang P, Nakamura Y, Lathrop GM, White R, Wasmuth JJ, Wood S, Berdahl LD, Leysens NJ | title = A detailed multipoint map of human chromosome 4 provides evidence for linkage heterogeneity and position-specific recombination rates | journal = American Journal of Human Genetics | volume = 48 | issue = 5 | pages = 911–925 | date = May 1991 | pmid = 1673289 | pmc = 1683054 }}
* {{cite journal | vauthors = Bodfish P, Warne D, Watkins C, Nyberg K, Spurr NK | title = Dinucleotide repeat polymorphism in the human coagulation factor XI gene, intron B (F11), detected using the polymerase chain reaction | journal = Nucleic Acids Research | volume = 19 | issue = 24 | pages = 6979 | year = 1992 | pmid = 1762944 | pmc = 329377 | doi = 10.1093/nar/19.24.6979-a }}
* {{cite journal | vauthors = Clarkson K, Rosenfeld B, Fair J, Klein A, Bell W | title = Factor XI deficiency acquired by liver transplantation | journal = Annals of Internal Medicine | volume = 115 | issue = 11 | pages = 877–879 | date = Dec 1991 | pmid = 1952475 | doi = 10.7326/0003-4819-115-11-877 }}
* {{cite journal | vauthors = McMullen BA, Fujikawa K, Davie EW | title = Location of the disulfide bonds in human coagulation factor XI: the presence of tandem apple domains | journal = Biochemistry | volume = 30 | issue = 8 | pages = 2056–2060 | date = Feb 1991 | pmid = 1998667 | doi = 10.1021/bi00222a008 }}
* {{cite journal | vauthors = Naito K, Fujikawa K | title = Activation of human blood coagulation factor XI independent of factor XII. Factor XI is activated by thrombin and factor XIa in the presence of negatively charged surfaces | journal = The Journal of Biological Chemistry | volume = 266 | issue = 12 | pages = 7353–7358 | date = Apr 1991 | pmid = 2019570 | doi = 10.1016/S0021-9258(20)89453-8 | doi-access = free }}
* {{cite journal | vauthors = Asakai R, Chung DW, Davie EW, Seligsohn U | title = Factor XI deficiency in Ashkenazi Jews in Israel | journal = The New England Journal of Medicine | volume = 325 | issue = 3 | pages = 153–158 | date = Jul 1991 | pmid = 2052060 | doi = 10.1056/NEJM199107183250303 | doi-access = free }}
* {{cite journal | vauthors = España F, Berrettini M, Griffin JH | title = Purification and characterization of plasma protein C inhibitor | journal = Thrombosis Research | volume = 55 | issue = 3 | pages = 369–384 | date = Aug 1989 | pmid = 2551064 | doi = 10.1016/0049-3848(89)90069-8 }}
* {{cite journal | vauthors = Asakai R, Chung DW, Ratnoff OD, Davie EW | title = Factor XI (plasma thromboplastin antecedent) deficiency in Ashkenazi Jews is a bleeding disorder that can result from three types of point mutations | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 86 | issue = 20 | pages = 7667–7671 | date = Oct 1989 | pmid = 2813350 | pmc = 298131 | doi = 10.1073/pnas.86.20.7667 | bibcode = 1989PNAS...86.7667A | doi-access = free }}
* {{cite journal | vauthors = Asakai R, Davie EW, Chung DW | title = Organization of the gene for human factor XI | journal = Biochemistry | volume = 26 | issue = 23 | pages = 7221–7228 | year = 1988 | pmid = 2827746 | doi = 10.1021/bi00397a004 }}
* {{cite journal | vauthors = Fujikawa K, Chung DW, Hendrickson LE, Davie EW | title = Amino acid sequence of human factor XI, a blood coagulation factor with four tandem repeats that are highly homologous with plasma prekallikrein | journal = Biochemistry | volume = 25 | issue = 9 | pages = 2417–2424 | date = May 1986 | pmid = 3636155 | doi = 10.1021/bi00357a018 }}
* {{cite journal | vauthors = Warn-Cramer BJ, Bajaj SP | title = Stoichiometry of binding of high molecular weight kininogen to factor XI/XIa | journal = Biochemical and Biophysical Research Communications | volume = 133 | issue = 2 | pages = 417–422 | year = 1986 | pmid = 3936495 | doi = 10.1016/0006-291X(85)90922-2 }}
* {{cite journal | vauthors = Bouma BN, Vlooswijk RA, Griffin JH | title = Immunologic studies of human coagulation factor XI and its complex with high molecular weight kininogen | journal = Blood | volume = 62 | issue = 5 | pages = 1123–1131 | date = Nov 1983 | pmid = 6626744 | doi = 10.1182/blood.V62.5.1123.1123 | doi-access = free }}
* {{cite journal | vauthors = Tuszynski GP, Bevacqua SJ, Schmaier AH, Colman RW, Walsh PN | title = Factor XI antigen and activity in human platelets | journal = Blood | volume = 59 | issue = 6 | pages = 1148–1156 | date = Jun 1982 | pmid = 7044446 | doi = 10.1182/blood.V59.6.1148.1148 | doi-access = free }}
* {{cite journal | vauthors = Imanaka Y, Lal K, Nishimura T, Bolton-Maggs PH, Tuddenham EG, McVey JH | title = Identification of two novel mutations in non-Jewish factor XI deficiency | journal = British Journal of Haematology | volume = 90 | issue = 4 | pages = 916–920 | date = Aug 1995 | pmid = 7669672 | doi = 10.1111/j.1365-2141.1995.tb05215.x | s2cid = 21900907 }}
* {{cite journal | vauthors = Pugh RE, McVey JH, Tuddenham EG, Hancock JF | title = Six point mutations that cause factor XI deficiency | journal = Blood | volume = 85 | issue = 6 | pages = 1509–1516 | date = Mar 1995 | pmid = 7888672 | doi = 10.1182/blood.V85.6.1509.bloodjournal8561509 | doi-access = free }}
* {{cite journal | vauthors = Riley PW, Cheng H, Samuel D, Roder H, Walsh PN | title = Dimer dissociation and unfolding mechanism of coagulation factor XI apple 4 domain: spectroscopic and mutational analysis | journal = Journal of Molecular Biology | volume = 367 | issue = 2 | pages = 558–573 | date = Mar 2007 | pmid = 17257616 | pmc = 1945241 | doi = 10.1016/j.jmb.2006.12.066 }}
* {{cite journal | vauthors = Samuel D, Cheng H, Riley PW, Canutescu AA, Nagaswami C, Weisel JW, Bu Z, Walsh PN, Roder H | title = Solution structure of the A4 domain of factor XI sheds light on the mechanism of zymogen activation | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 40 | pages = 15693–15698 | date = Oct 2007 | pmid = 17884987 | pmc = 1987390 | doi = 10.1073/pnas.0703080104 | bibcode = 2007PNAS..10415693S | doi-access = free }}
{{Refend}}

== External links ==
* The [[MEROPS]] online database for peptidases and their inhibitors: [http://merops.sanger.ac.uk/cgi-bin/merops.cgi?id=S01.213 S01.213] {{Webarchive|url=https://web.archive.org/web/20200529050416/https://www.ebi.ac.uk/merops/ |date=2020-05-29 }}
{{PDB Gallery|geneid=2160}}

{{Coagulation}}
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{{DEFAULTSORT:Factor Xi}}
[[Category:EC 3.4.21]]
[[Category:Coagulation system]]
[[Category:Zymogens]]