Department of Genome Sciences, University of Washington, Seattle, United States
Nathan J Rollins
Department of Systems Biology, Harvard Medical School, Boston, United States
Jason J Stephany
Department of Genome Sciences, University of Washington, Seattle, United States
Katherine A Sitko
Department of Genome Sciences, University of Washington, Seattle, United States
Kenneth A Matreyek
Department of Genome Sciences, University of Washington, Seattle, United States
Marta Verby
Donnelly Centre and Departments of Molecular Genetics and Computer Science, University of Toronto, and Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Canada
Song Sun
Donnelly Centre and Departments of Molecular Genetics and Computer Science, University of Toronto, and Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Canada
Frederick P Roth
Donnelly Centre and Departments of Molecular Genetics and Computer Science, University of Toronto, and Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Canada
Department of Genome Sciences, University of Washington, Seattle, United States; Department of Bioengineering, University of Washington, Seattle, United States
Vitamin K epoxide reductase (VKOR) drives the vitamin K cycle, activating vitamin K-dependent blood clotting factors. VKOR is also the target of the widely used anticoagulant drug, warfarin. Despite VKOR’s pivotal role in coagulation, its structure and active site remain poorly understood. In addition, VKOR variants can cause vitamin K-dependent clotting factor deficiency or alter warfarin response. Here, we used multiplexed, sequencing-based assays to measure the effects of 2,695 VKOR missense variants on abundance and 697 variants on activity in cultured human cells. The large-scale functional data, along with an evolutionary coupling analysis, supports a four transmembrane domain topology, with variants in transmembrane domains exhibiting strongly deleterious effects on abundance and activity. Functionally constrained regions of the protein define the active site, and we find that, of four conserved cysteines putatively critical for function, only three are absolutely required. Finally, 25% of human VKOR missense variants show reduced abundance or activity, possibly conferring warfarin sensitivity or causing disease.
