Vitamin K epoxide reductase

Vitamin K epoxide reductase (warfarin-sensitive)
Reaction
Identifiers
EC no.	1.17.4.4
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
Search PMC articles PubMed articles NCBI proteins

Vitamin K epoxide reductase
Structure of a bacterial VKOR, membrane denoted as lines (PDB: 3KP9​).
Identifiers
Symbol	VKOR
Pfam	PF07884
InterPro	IPR012932
CATH	3kp9
TCDB	9.B.265
OPM superfamily	18
OPM protein	3kp9
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Vitamin K epoxide reductase (VKOR) is an enzyme (EC 1.17.4.4) that reduces vitamin K 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 and archaea.^[1] In some plant and bacterial homologues, the VKOR domain is fused with domains of the thioredoxin family of oxidoreductases.^[1]

Four cysteine residues and one residue, which is either serine or threonine, are identified as likely active-site residues.^[1] 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 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).^[2][3]

The human gene for VKOR is called VKORC1 (VKOR complex subunit 1). It is the target of anticoagulant warfarin. Its partner is a redox protein with an unknown identity,^[4][5] probably a thioredoxin-like protein located in the ER lumen such as TMX1.^[6]

There is also a similar gene called VKORC1L1. The VKORL1 complex it forms is much less efficient at reducing the epoxide, but it has the ability to reduce the quinone form of vitamin K to a diol form (KH₂). Although EC 1.17.4.4 notes both paralogs as having both activities, the precise division of labor in vitro is debated.^[7]

References

1. Goodstadt L, Ponting CP (June 2004). "Vitamin K epoxide reductase: homology, active site and catalytic mechanism". Trends in Biochemical Sciences. 29 (6): 289–92. doi:10.1016/j.tibs.2004.04.004. PMID 15276181.
2. Li W, Schulman S, Dutton RJ, Boyd D, Beckwith J, Rapoport TA (January 2010). "Structure of a bacterial homologue of vitamin K epoxide reductase". Nature. 463 (7280): 507–12. Bibcode:2010Natur.463..507L. doi:10.1038/nature08720. PMC 2919313. PMID 20110994.
3. Rishavy MA, Usubalieva A, Hallgren KW, Berkner KL (March 2011). "Novel insight into the mechanism of the vitamin K oxidoreductase (VKOR): electron relay through Cys43 and Cys51 reduces VKOR to allow vitamin K reduction and facilitation of vitamin K-dependent protein carboxylation". The Journal of Biological Chemistry. 286 (9): 7267–78. doi:10.1074/jbc.M110.172213. PMC 3044983. PMID 20978134.
4. Li T, Chang CY, Jin DY, Lin PJ, Khvorova A, Stafford DW (February 2004). "Identification of the gene for vitamin K epoxide reductase". Nature. 427 (6974): 541–4. Bibcode:2004Natur.427..541L. doi:10.1038/nature02254. PMID 14765195. S2CID 4424554.
5. Rost S, Fregin A, Ivaskevicius V, Conzelmann E, Hörtnagel K, Pelz HJ, Lappegard K, Seifried E, Scharrer I, Tuddenham EG, Müller CR, Strom TM, Oldenburg J (February 2004). "Mutations in VKORC1 cause warfarin resistance and multiple coagulation factor deficiency type 2". Nature. 427 (6974): 537–41. Bibcode:2004Natur.427..537R. doi:10.1038/nature02214. PMID 14765194. S2CID 4424197.
6. Schulman, Sol; Wang, Belinda; Li, Weikai; Rapoport, Tom A. (24 August 2010). "Vitamin K epoxide reductase prefers ER membrane-anchored thioredoxin-like redox partners". Proceedings of the National Academy of Sciences. 107 (34): 15027–15032. Bibcode:2010PNAS..10715027S. doi:10.1073/pnas.1009972107. PMC 2930587. PMID 20696932.
7. Shearer MJ, Newman P (March 2014). "Recent trends in the metabolism and cell biology of vitamin K with special reference to vitamin K cycling and MK-4 biosynthesis". Journal of Lipid Research. 55 (3): 345–362. doi:10.1194/jlr.R045559. PMC 3934721. PMID 24489112.

This article incorporates text from the public domain Pfam and InterPro: IPR012932