Factor IX

Factor IX (EC 3.4.21.22), also known as Christmas factor, is one of the serine proteases involved in coagulation; it belongs to peptidase family S1. Deficiency of this protein causes haemophilia B.

F9
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 1CFH, 1CFI, 1EDM, 1IXA, 1MGX, 1NL0, 1RFN, 2WPH, 2WPI, 2WPJ, 2WPK, 2WPL, 2WPM, 3KCG, 3LC3, 3LC5, 4YZU, 4Z0K, 4ZAE, 4WM0, 4WMA, 4WMI, 4WMK, 4WN2, 4WNH, 5EGM, 5JBC, 5JB9, 5JBB, 5JB8, 5JBA
Identifiers
Aliases	F9, F9 p22, FIX, HEMB, P19, PTC, THPH8, coagulation factor IX, Blood coagulation factor IX, Christmas Factor
External IDs	OMIM: 300746; MGI: 88384; HomoloGene: 106; GeneCards: F9; OMA:F9 - orthologs
Gene location (Human) Chr. X chromosome (human)[1] Band Xq27.1 Start 139,530,739 bp[1] End 139,563,459 bp[1]
Gene location (Mouse) Chr. X chromosome (mouse)[2] Band X A6|X 33.5 cM Start 59,044,824 bp[2] End 59,076,119 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in right lobe of liver secondary oocyte gonad pancreatic ductal cell skin of thigh kidney blood human musculoskeletal system muscular system muscle Top expressed in left lobe of liver lumbar spinal ganglion gallbladder sexually immature organism thoracic diaphragm medial head of gastrocnemius muscle dentate gyrus nucleus of stria terminalis piriform cortex jejunum More reference expression data BioGPS More reference expression data
Gene ontology Molecular function endopeptidase activity metal ion binding peptidase activity serine-type peptidase activity hydrolase activity calcium ion binding serine-type endopeptidase activity protein binding Cellular component endoplasmic reticulum lumen plasma membrane Golgi lumen extracellular exosome extracellular region extracellular space collagen-containing extracellular matrix Biological process hemostasis blood coagulation, intrinsic pathway zymogen activation endoplasmic reticulum to Golgi vesicle-mediated transport signal peptide processing blood coagulation, extrinsic pathway peptidyl-glutamic acid carboxylation proteolysis blood coagulation Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 2158 14071 Ensembl ENSG00000101981 ENSMUSG00000031138 UniProt P00740 P16294 RefSeq (mRNA) NM_000133 NM_001313913 NM_007979 NM_001305797 RefSeq (protein) NP_000124 NP_001300842 NP_001292726 NP_032005 Location (UCSC) Chr X: 139.53 – 139.56 Mb Chr X: 59.04 – 59.08 Mb PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

It was discovered in 1952 after a young boy named Stephen Christmas was found to be lacking this exact factor, leading to haemophilia.^[5] Coagulation factor IX is on the World Health Organization's List of Essential Medicines.^[6]

Physiology

The blood coagulation and Protein C pathway.

Factor IX is produced as a zymogen, an inactive precursor. It is processed to remove the signal peptide, glycosylated and then cleaved by factor XIa (of the contact pathway) or factor VIIa (of the tissue factor pathway) to produce a two-chain form, where the chains are linked by a disulfide bridge.^[7][8] When activated into factor IXa, in the presence of Ca²⁺, membrane phospholipids, and a Factor VIII cofactor, it hydrolyses one arginine-isoleucine bond in factor X to form factor Xa.

Factor IX is inhibited by antithrombin.^[7]

Factor IX expression increases with age in humans and mice. In mouse models, mutations within the promoter region of factor IX have an age-dependent phenotype.^[9]

Domain architecture

Factors VII, IX, and X all play key roles in blood coagulation and also share a common domain architecture.^[10] The factor IX protein is composed of four protein domains: the Gla domain, two tandem copies of the EGF domain and a C-terminal trypsin-like peptidase domain which carries out the catalytic cleavage.

Human factor IX protein domain architecture, where each protein domain is represented by a coloured box

The N-terminal EGF domain has been shown to at least in part be responsible for binding tissue factor.^[10] Wilkinson et al. conclude that residues 88 to 109 of the second EGF domain mediate binding to platelets and assembly of the factor X activating complex.^[11]

The structures of all four domains have been solved. A structure of the two EGF domains and the trypsin-like domain was determined for the pig protein.^[12] The structure of the Gla domain, which is responsible for Ca(II)-dependent phospholipid binding, was also determined by NMR.^[13]

Several structures of 'super active' mutants have been solved,^[14] which reveal the nature of factor IX activation by other proteins in the clotting cascade.

Genetics

In human, the F9 gene is located on the X chromosome at position q27.1.

Because the gene for factor IX is located on the X chromosome (Xq27.1-q27.2), loss-of-function mutations thereof are X-linked recessive: males experience the disease phenotype much more frequently than females. At least 534 disease-causing mutations in this gene have been discovered.^[15] The F9 gene was first cloned in 1982 by Kotoku Kurachi and Earl Davie.^[16]

Polly, a transgenic cloned Poll Dorset sheep carrying the gene for factor IX, was produced by Dr Ian Wilmut at the Roslin Institute in 1997.^[17]

Role in disease

See also: Prothrombin complex concentrate

Factor IX
INN: nonacog alfa

Clinical data
Trade names	Benefix
License data	US DailyMed: Coagulation Factor IX
ATC code	None
Legal status
Legal status	AU: S4 (Prescription only)

Factor IX
INN: nonacog gamma

Clinical data
Trade names	Rixubis
Routes of administration	Intravenous
ATC code	None
Legal status
Legal status	EU: Rx-only[18]

Factor IX
INN: albutrepenonacog alfa

Clinical data
Trade names	Idelvion
License data	US DailyMed: Coagulation Factor IX
ATC code	None
Legal status
Legal status	AU: S4 (Prescription only) CA: ℞-only[19]

Factor IX
INN: eftrenonacog alfa

Clinical data
Trade names	Alprolix
License data	US DailyMed: Coagulation Factor IX
ATC code	None
Legal status
Legal status	AU: S4 (Prescription only) EU: Rx-only[20]

Factor IX
INN: nonacog beta pegol

Clinical data
Trade names	Refixia
ATC code	None
Legal status
Legal status	AU: S4 (Prescription only)[21]

Deficiency of factor IX causes Christmas disease (hemophilia B).^[5] Over 3000 variants of factor IX have been described, affecting 73% of the 461 residues;^[22] some cause no symptoms, but many lead to a significant bleeding disorder. The original Christmas disease mutation was identified by sequencing of Christmas' DNA, revealing a mutation which changed a cysteine to a serine.^[23] Recombinant factor IX is used to treat Christmas disease. Formulations include:

• nonacog alfa (brand name Benefix)^[24]
• nonacog gamma (brand name Rixubis)^[18]
• albutrepenonacog alfa (brand name Idelvion)^[25]
• eftrenonacog alfa (brand name Alprolix)^[26]
• nonacog beta pegol (brand name Refixia)^[27]
• coagulation factor IX [recombinant] (Benefix)^[28]
• coagulation factor IX [recombinant] (Idelvion)^[29]
• coagulation factor IX (recombinant), Fc fusion protein (Alprolix)^[30]
• coagulation factor IX [recombinant] (Ixinity)^[31][32]
• coagulation factor IX [recombinant] (Rebinyn)^[33]
• coagulation factor IX [recombinant] (Rixubis)^[34]
• coagulation factor IX (human) (Alphanine SD)^[35]

Some rare mutations of factor IX result in elevated clotting activity, and can result in clotting diseases, such as deep vein thrombosis. This gain of function mutation renders the protein hyperfunctional and is associated with familial early-onset thrombophilia.^[36]

Factor IX deficiency is treated by injection of purified factor IX produced through cloning in various animal or animal cell vectors. Tranexamic acid may be of value in patients undergoing surgery who have inherited factor IX deficiency in order to reduce the perioperative risk of bleeding.^[37]

A list of all the mutations in Factor IX is compiled and maintained by EAHAD.^[38]

Coagulation factor IX is on the World Health Organization's List of Essential Medicines.^[6]