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Identification of UBIAD1 as a novel human menaquinone-4 biosynthetic enzyme


Vitamin K occurs in the natural world in several forms, including a plant form, phylloquinone (PK), and a bacterial form, menaquinones (MKs). In many species, including humans, PK is a minor constituent of hepatic vitamin K content, with most hepatic vitamin K content comprising long-chain MKs. Menaquinone-4 (MK-4) is ubiquitously present in extrahepatic tissues, with particularly high concentrations in the brain, kidney and pancreas of humans and rats1,2,3. It has consistently been shown that PK is endogenously converted to MK-4 (refs 4–8). This occurs either directly within certain tissues or by interconversion to menadione (K3), followed by prenylation to MK-4 (refs 9–12). No previous study has sought to identify the human enzyme responsible for MK-4 biosynthesis. Previously we provided evidence for the conversion of PK and K3 into MK-4 in mouse cerebra13. However, the molecular mechanisms for these conversion reactions are unclear. Here we identify a human MK-4 biosynthetic enzyme. We screened the human genome database for prenylation enzymes and found UbiA prenyltransferase containing 1 (UBIAD1), a human homologue of Escherichia coli prenyltransferase menA. We found that short interfering RNA against the UBIAD1 gene inhibited the conversion of deuterium-labelled vitamin K derivatives into deuterium-labelled-MK-4 (MK-4-d7) in human cells. We confirmed that the UBIAD1 gene encodes an MK-4 biosynthetic enzyme through its expression and conversion of deuterium-labelled vitamin K derivatives into MK-4-d7 in insect cells infected with UBIAD1 baculovirus. Converted MK-4-d7 was chemically identified by 2H-NMR analysis. MK-4 biosynthesis by UBIAD1 was not affected by the vitamin K antagonist warfarin. UBIAD1 was localized in endoplasmic reticulum and ubiquitously expressed in several tissues of mice. Our results show that UBIAD1 is a human MK-4 biosynthetic enzyme; this identification will permit more effective decisions to be made about vitamin K intake and bone health.

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Figure 1: Conversion activities of deuterium-labelled vitamins K.
Figure 2: Conversion activity of UBIAD1 in MG-63 cells.
Figure 3: MK-4 biosynthetic activity of UBIAD1 in Sf9 cells and effects of warfarin on MK-4 biosynthesis.
Figure 4: Subcellular localization of UBIAD1 in MG-63 cells, UBIAD1 activity in microsomes from UBIAD1 baculovirus-infected Sf9 cells, and scheme of UBIAD1 activity.


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We thank M. Sugiura and A. Takeuchi for technical support with 2H-NMR analysis and LC-APCI-MS/MS analysis. This work was supported in part by priority areas from the Ministry of Education, Culture, Sports, Science and Technology (to K.N. and T.O.).

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K.N. and T.O. planned the project and analysed the experiments, together with Y.H., N.S., N.Y., M.W., Y.U., N.O., Y.S. and Y.S. The manuscript was written by K.N. and T.O., and all authors commented on it.

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Correspondence to Toshio Okano.

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The authors declare no competing financial interests.

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Nakagawa, K., Hirota, Y., Sawada, N. et al. Identification of UBIAD1 as a novel human menaquinone-4 biosynthetic enzyme. Nature 468, 117–121 (2010).

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