Vitamin K epoxide reductase (VKOR) is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

() that reduces

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 ...

after it has been oxidised in the carboxylation of glutamic acid residues in blood coagulation enzymes. VKOR is a member of a large family of predicted enzymes that are present in vertebrates, ''Drosophila'', plants,

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

and

archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

. In some

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

and

l homologues, the VKOR

domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function * Do ...

is fused with domains of the

thioredoxin Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes, including redox signaling. In humans, thioredoxins are encoded by ''TXN'' and '' TXN2'' genes. Loss-of-fu ...

family of

oxidoreductases In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually uti ...

. Four cysteine residues and one residue, which is either serine or threonine, are identified as likely active-site

residue Residue may refer to: Chemistry and biology * An amino acid, within a peptide chain * Crop residue, materials left after agricultural processes * Pesticide residue, refers to the pesticides that may remain on or in food after they are applied ...

s. Solved bacterial VKOR structures has enabled more insights into the catalytic mechanism. All VKORs are transmembrane proteins with at least three TM helices at the catalytic core. The quinone to be reduced is bound by a redox-active CXXC motif in the C-terminal helices, similar to the

DsbB Disulfide bond formation protein B (DsbB) is a protein component of the pathway that leads to disulfide bond formation in periplasmic proteins of ''Escherichia coli'' () and other bacteria. In ''Bacillus subtilis'' it is known as ''BdbC'' (). T ...

active site. Two other cysteines to the N-terminal are located in a loop outside of the transmembrane region; they relay electrons with a redox protein (or in the case of the bacterial homolog, its own fused domain). The human gene for VKOR is called

VKORC1 The human gene ''VKORC1'' encodes for the enzyme, Vitamin K epOxide Reductase Complex (VKORC) subunit 1. This enzymatic protein complex is responsible for reducing vitamin K 2,3-epoxide to its active form, which is important for effective clottin ...

(VKOR complex subunit 1). It is the target of anticoagulant

warfarin Warfarin, sold under the brand name Coumadin among others, is a medication that is used as an anticoagulant (blood thinner). It is commonly used to prevent blood clots such as deep vein thrombosis and pulmonary embolism, and to prevent st ...

. Its partner is a redox protein with an unknown identity. There is also a similar gene called VKORC1L1.

References

{{InterPro content, IPR012932 EC 1.17.4