Factor V (pronounced factor five) is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
of the
coagulation
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism ...
system, rarely referred to as proaccelerin or labile factor. In contrast to most other coagulation factors, it is not enzymatically active but functions as a
cofactor. Deficiency leads to predisposition for
hemorrhage
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, v ...
, while some mutations (most notably
factor V Leiden
Factor V Leiden (rs6025 or ''F5'' p.R506Q) is a variant (mutated form) of human factor V (one of several substances that helps blood clot), which causes an increase in blood clotting (hypercoagulability). Due to this mutation, protein C, an antico ...
) predispose for
thrombosis
Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (th ...
.
Genetics
The
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
for factor V is located on the
first chromosome (1q24). It is genomically related to the family of
multicopper oxidases, and is homologous to coagulation
factor VIII. The gene spans 70 kb, consists of 25 exons, and the resulting protein has a relative molecular mass of approximately 330kDa.
Structure
Factor V protein consists of six domains: A1-A2-B-A3-C1-C2.
The A domains are
homologous to the A domains of the copper-binding protein
ceruloplasmin, and form a triangular as in that protein. A copper ion is bound in the A1-A3 interface, and A3 interacts with the plasma.
The C domains belong to the
phospholipid
Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
-binding
discoidin domain family (unrelated to
C2 domain), and the C2 domain mediates membrane binding. The B domain
C-terminus
The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein i ...
acts as a
cofactor for the
anticoagulant
Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where t ...
protein C activation by
protein S.
Activation of factor V to factor Va is done by cleavage and release of the B domain, after which the protein no longer assists in activating protein C. The protein is now divided to a heavy chain, consisting of the A1-A2 domains, and a light chain, consisting of the A3-C1-C2 domains. Both form non-covalently a complex in a calcium-dependent manner. This complex is the pro-coagulant factor Va.
Physiology
Factor V synthesis occurs in the liver, principally. The molecule circulates in plasma as a single-chain molecule with a plasma half-life of 12–36 hours.
Factor V is able to bind to activated
platelets and is activated by
thrombin. On activation, factor V is spliced in two chains (heavy and light chain with molecular masses of 110000 and 73000, respectively) which are noncovalently bound to each other by
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
. The thereby activated factor V (now called FVa) is a cofactor of the
prothrombinase complex: The activated
factor X (FXa) enzyme requires calcium and activated factor V (FVa) to convert prothrombin to
thrombin on the cell surface membrane.
Factor Va is degraded by
activated protein C
Protein C, also known as autoprothrombin IIA and blood coagulation factor XIX, is a zymogen, that is, an inactive enzyme. The activated form plays an important role in regulating anticoagulation, inflammation, and cell death and maintaining ...
, one of the principal physiological inhibitors of coagulation. In the presence of
thrombomodulin, thrombin acts to decrease clotting by activating protein C; therefore, the concentration and action of protein C are important determinants in the negative feedback loop through which thrombin limits its own activation.
Role in disease
Various hereditary disorders of factor V are known. Deficiency is associated with a rare mild form of
hemophilia
Haemophilia, or hemophilia (), is a mostly inherited genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. This results in people bleeding for a longer time after an injury, easy bruising ...
(termed parahemophilia or Owren parahemophilia), the incidence of which is about 1:1,000,000. It inherits in an
autosomal recessive
In genetics, dominance is the phenomenon of one variant ( allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant an ...
fashion.
There exists a bleeding tendency associated with the genetic up‐regulation of FV‐short, a minor splicing isoform of FV. This abnormal bleeding tendency occurs in east Texas bleeding disorder, Amsterdam bleeding disorder, and a third and more extreme example described in 2021 by Karen L. Zimowski ''et al.''
Other
mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, m ...
s of factor V are associated with
venous thrombosis
Venous thrombosis is blockage of a vein caused by a thrombus (blood clot). A common form of venous thrombosis is deep vein thrombosis (DVT), when a blood clot forms in the deep veins. If a thrombus breaks off (embolizes) and flows to the lungs t ...
. They are the most common hereditary causes for
thrombophilia
Thrombophilia (sometimes called hypercoagulability or a prothrombotic state) is an abnormality of blood coagulation that increases the risk of thrombosis (blood clots in blood vessels). Such abnormalities can be identified in 50% of people who ...
(a tendency to form
blood clot
A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cr ...
s). The most common one of these,
factor V Leiden
Factor V Leiden (rs6025 or ''F5'' p.R506Q) is a variant (mutated form) of human factor V (one of several substances that helps blood clot), which causes an increase in blood clotting (hypercoagulability). Due to this mutation, protein C, an antico ...
, is due to the replacement of an
arginine
Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the am ...
residue with
glutamine
Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...
at amino acid position 506 (R506Q). All prothrombotic factor V mutations (factor V Leiden, factor V Cambridge, factor V Hong Kong) make it resistant to cleavage by activated protein C ("APC resistance"). It therefore remains active and increases the rate of thrombin generation.
History
Until the discovery of factor V, coagulation was regarded as a product of four factors:
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
(IV) and thrombokinase (III) together acting on
prothrombin (II) to produce
fibrinogen (I); this model had been outlined by
Paul Morawitz
Paul Oskar Morawitz (April 3, 1879 in St. Petersburg – July 1, 1936) was a German internist and physiologist whose most important work was in studying the coagulation of blood.
After completing his medical studies at Leipzig (in 1901) he compl ...
in 1905.
The suggestion that an additional factor might exist was made by (1905–1990), a
Norwegian physician, during his investigations into the bleeding tendency of a lady called Mary (1914–2002). She had suffered from
nosebleeds and
menorrhagia
Heavy menstrual bleeding (HMB), previously known as menorrhagia or hypermenorrhea, is a menstrual period with excessively heavy flow. It is a type of abnormal uterine bleeding (AUB).
Abnormal uterine bleeding can be caused by structural abnor ...
(excessive menstrual blood loss) for most her life, and was found to have a prolonged
prothrombin time, suggesting either
vitamin K
Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation ...
deficiency or
chronic liver disease leading to prothrombin deficiency. However, neither were the case, and Owren demonstrated this by correcting the abnormality with plasma from which prothrombin had been removed. Using Mary's serum as index, he found that the "missing" factor, which he labeled V (I–IV having been used in Morawitz' model), had particular characteristics. Most investigations were performed during the
Second World War
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposi ...
, and while Owren published his results in Norway in 1944, he could not publish them internationally until the war was over. They appeared finally in ''
The Lancet
''The Lancet'' is a weekly peer-reviewed general medical journal and one of the oldest of its kind. It is also the world's highest-impact academic journal. It was founded in England in 1823.
The journal publishes original research articles ...
'' in 1947.
[
The possibility of an extra coagulation factor was initially resisted on methodological grounds by Drs Armand Quick and Walter Seegers, both world authorities in coagulation. Confirmatory studies from other groups led to their final approval several years later.][
Owren initially felt that factor V (labile factor or proaccelerin) activated another factor, which he named VI. VI was the factor that accelerated the conversion from prothrombin to thrombin. It was later discovered that factor V was "converted" (activated) by thrombin itself, and later still that factor VI was simply the activated form of factor V.][
The complete amino acid sequence of the protein was published in 1987. In 1994 ]factor V Leiden
Factor V Leiden (rs6025 or ''F5'' p.R506Q) is a variant (mutated form) of human factor V (one of several substances that helps blood clot), which causes an increase in blood clotting (hypercoagulability). Due to this mutation, protein C, an antico ...
, resistant to inactivation by protein C, was described; this abnormality is the most common genetic cause for thrombosis
Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (th ...
.
Interactions
Factor V has been shown to interact
Advocates for Informed Choice, doing business as, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex trai ...
with Protein S.
References
Further reading
*
*
*
*
*
*
*
*
External links
The Coagulation Factor V Protein
*
{{Coagulation
Coagulation system