The long-term objective of this project is to understand, not only the structure and function of the vitamin K epoxide reductase (VKOR), but also the vitamin K cycle as a whole. Vitamin K-dependent carboxylation is an essential post-translational modification for proteins important in several physiologic functions, including blood coagulation and bone metabolism. VKOR is the target of warfarin, the most widely prescribed anti-coagulant for thromboembolic disorders. Although estimated to prevent twenty strokes per induced bleeding episode, warfarin is still under-utilized because of fear of bleeding. It is hoped that research funded by this grant will lead to improved anti- thrombotic therapies that will avoid some of the problems related to warfarin treatment. Specifically, we propose to accomplish the following during the tenure of this grant: (1) using standard purification and enzyme assay methods, RNAi technologies, and modified expression cloning, we will investigate the vitamin K cycle to identify components other than the vitamin K epoxide reductase (VKOR) necessary for the production of vitamin K hydroquinone, (2) employing electron crystallography, biochemical and molecular biological techniques, conduct studies to elucidate the three- dimensional structure of VKOR, and (3) using both in vivo and in vitro methods investigate the structural characteristics necessary for VKOR.
In addition to development of new ways of controlling thromboses, knowledge gained from our research on the vitamin K cycle should give insight into the vitamin's apparently major role in bone formation. While the contribution to bone metabolism is clear, it is still controversial whether vitamin K is useful in treating or slowing progression of bone density loss in osteoporosis. Another developing area relevant to public health is the role of coagulation/thrombosis in cancer, and in turn whether vitamin K and its antagonists have a place in cancer treatment.
|Tie, Jian-Ke; Jin, Da-Yun; Stafford, Darrel W (2014) Conserved loop cysteines of vitamin K epoxide reductase complex subunit 1-like 1 (VKORC1L1) are involved in its active site regeneration. J Biol Chem 289:9396-407|
|Tie, J-K; Jin, D-Y; Tie, K et al. (2013) Evaluation of warfarin resistance using transcription activator-like effector nucleases-mediated vitamin K epoxide reductase knockout HEK293 cells. J Thromb Haemost 11:1556-64|
|Ingram, Brian O; Turbyfill, Jared L; Bledsoe, Peggy J et al. (2013) Assessment of the contribution of NAD(P)H-dependent quinone oxidoreductase 1 (NQO1) to the reduction of vitamin K in wild-type and NQO1-deficient mice. Biochem J 456:47-54|
|Tie, Jian-Ke; Jin, Da-Yun; Stafford, Darrel W (2012) Mycobacterium tuberculosis vitamin K epoxide reductase homologue supports vitamin K-dependent carboxylation in mammalian cells. Antioxid Redox Signal 16:329-38|
|Wu, Sangwook; Liu, Shubin; Davis, Charles H et al. (2011) A hetero-dimer model for concerted action of vitamin K carboxylase and vitamin K reductase in vitamin K cycle. J Theor Biol 279:143-9|
|Tie, Jian-Ke; Jin, Da-Yun; Straight, David L et al. (2011) Functional study of the vitamin K cycle in mammalian cells. Blood 117:2967-74|
|Jin, Da-Yun; Tie, Jian-Ke; Stafford, Darrel W (2007) The conversion of vitamin K epoxide to vitamin K quinone and vitamin K quinone to vitamin K hydroquinone uses the same active site cysteines. Biochemistry 46:7279-83|
|Chu, Pei-Hsuan; Huang, Teng-Yi; Williams, Jason et al. (2006) Purified vitamin K epoxide reductase alone is sufficient for conversion of vitamin K epoxide to vitamin K and vitamin K to vitamin KH2. Proc Natl Acad Sci U S A 103:19308-13|