The Arg98Trp mutation in human VKORC1 causing VKCFD2 disrupts a di-arginine-based ER retention motif

Blood. 2014 Aug 21;124(8):1354-62. doi: 10.1182/blood-2013-12-545988. Epub 2014 Jun 24.

Abstract

Vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) is an enzyme localized to the endoplasmic reticulum (ER) membrane. VKORC1 catalyzes the reduction of vitamin K 2,3-epoxide to vitamin K and to vitamin K hydroquinone, the latter required by the enzyme γ-carboxylase for γ-carboxylation of all vitamin K-dependent (VKD) proteins. Until now, only 1 human VKORC1 mutation, p.Arg98Trp, is known to cause combined deficiency of VKD clotting factors type 2 (VKCFD2), a disease phenotype reported in 3 unrelated families. VKCFD2 patients suffer from spontaneous bleeding episodes because of decreased levels of γ-carboxylated VKD clotting factors. Daily supraphysiological vitamin K supplementation restores clotting for VKCFD2 patients and results in high serum levels of vitamin K 2,3-epoxide, suggesting that supplemented vitamin K is reduced in vivo. Although the p.Arg98Trp mutation results in reduced vitamin K 2,3-epoxide reductase activity, the molecular mechanism underlying this pathophysiology is unknown. Using a combination of in silico analysis and confocal microscopy, we demonstrate for the first time that VKORC1:p.Arg98Trp disrupts a di-arginine ER retention motif resulting in 20% ER colocalization only. As a consequence, VKORC1 exits the ER membrane by cellular quality control systems and results in the observed VKCFD2 phenotype.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Substitution
  • Blood Coagulation Factors / genetics
  • Blood Coagulation Factors / metabolism*
  • Cell Line
  • Endoplasmic Reticulum / enzymology*
  • Endoplasmic Reticulum / genetics
  • Humans
  • Mutation, Missense*
  • Protein Transport / physiology
  • Vitamin K / genetics
  • Vitamin K / metabolism*
  • Vitamin K Epoxide Reductases / genetics
  • Vitamin K Epoxide Reductases / metabolism*

Substances

  • Blood Coagulation Factors
  • Vitamin K
  • VKORC1 protein, human
  • Vitamin K Epoxide Reductases