A Dedicated Type II NADPH Dehydrogenase Performs the Penultimate Step in the Biosynthesis of Vitamin K₁ in Synechocystis and Arabidopsis

Authors

Abdelhak Fatihi, University of Nebraska–LincolnFollow
Scott Latimer, University of Nebraska-Lincoln
Stefan Schmollinger, University of California, Los Angeles
Anna Block, University of Nebraska-Lincoln
Patrick Dussault, University of Nebraska-LincolnFollow
Wim F.J. Vermaas, Arizona State University
Sabeeha S. Merchant, University of California, Los Angeles
Gilles J. Basset, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2015

Citation

The Plant Cell, Vol. 27: 1730–1741, June 2015

Comments

Copyright 2015 American Society of Plant Biologists. All rights reserved.

Abstract

Mutation of Arabidopsis thaliana NAD(P)H DEHYDROGENASE C1 (NDC1; At5g08740) results in the accumulation of demethylphylloquinone, a late biosynthetic intermediate of vitamin K₁. Gene coexpression and phylogenomics analyses showed that conserved functional associations occur between vitamin K biosynthesis and NDC1 homologs throughout the prokaryotic and eukaryotic lineages. Deletion of Synechocystis ndbB, which encodes for one such homolog, resulted in the same defects as those observed in the cyanobacterial demethylnaphthoquinone methyltransferase knockout. Chemical modeling and assay of purified demethylnaphthoquinone methyltransferase demonstrated that, by virtue of the strong electrophilic nature of S-adenosyl-Lmethionine, the transmethylation of the demethylated precursor of vitamin K is strictly dependent on the reduced form of its naphthoquinone ring. NDC1 was shown to catalyze such a prerequisite reduction by using NADPH and demethylphylloquinone as substrates and flavine adenine dinucleotide as a cofactor. NDC1 displayed Michaelis-Menten kinetics and was markedly inhibited by dicumarol, a competitive inhibitor of naphthoquinone oxidoreductases. These data demonstrate that the reduction of the demethylnaphthoquinone ring represents an authentic step in the biosynthetic pathway of vitamin K, that this reaction is enzymatically driven, and that a selection pressure is operating to retain type II NAD(P)H dehydrogenases in this process.