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

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 γcarboxylase for γcarboxylation 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 type2 (VKCFD2), a disease phenotype reported in 3 unrelated families. VKCFD2 patients suffer from spontaneous bleeding episodes because of decreased levels of γcarboxylated VKD clotting factors. Daily supraphysioiogical vitamin K supplementation restores clotting for VKCFD2 patients and results in high serum levelsof vitamin K 2,3-epoxide, suggesting that supplemented vitamin K is reduced in vivo. Although the p.Arg98Trp mutation results in reduced vitamin K2,3-epoxidereductase 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. (Blood.2014;124(8):1354-1362) [ABSTRACT FROM AUTHOR]