Journal
THROMBOSIS AND HAEMOSTASIS
Volume 94, Issue 4, Pages 780-786Publisher
GEORG THIEME VERLAG KG
DOI: 10.1160/TH05-02-0082
Keywords
vitamin K; VKOR; warfarin; CXXC motif; mutagenesis
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Coumarin and homologous compounds are the most widely used anticoagulant drugs worldwide. They function as antagonists of vitamin K, an essential cofactor for the posttranslational gamma-glutamyl carboxylation of the so-called vitamin K-dependent proteins. As vitamin K hydroquinone is converted to vitamin K epoxide (VKO) in every carboxylation step, the epoxide has to be recycled to the reduced form by the vitamin K epoxide reductase complex (VKOR). Recently, a single coumarin-sensitive protein of the putative VKOR enzyme complex was identified in humans (vitamin K epoxide reductase complex subunit 1, VKORC1). Mutations in VKORC1 result in two different phenotypes: warfarin resistance (WR) and multiple coagulation factor deficiency type 2 (VKCFD2). Here,we report on the expression of site-directed VKORC1 mutants, addressing possible structural and functional roles of all seven cysteine residues (Cys 16, Cys43, Cys51, Cys85, Cys96, Cys 132, Cys 135), the highly conserved residue Ser/Thr57, and Arg98, known to cause VKCFD2 in humans. Our results support the hypothesis that the CI32-X-X-C135 motif in VKORC1 comprises part of the redox active site that catalyzes VKO reduction and also suggest a crucial role for the hydrophobic Thr-Tyr-Ala motif in coumarin binding. Furthermore, our results support the concept that different structural components of VKORC1 define the binding sites for vitamin K epoxide and coumarin.
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