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

Abstract

Mutation of Arabidopsis thaliana NAD(P)H DEHYDROGENASE C1 (NDC1; At5g08740) results in the accumulation of demethylphylloquinone, a late biosynthetic intermediate of vitamin K 1 . 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.

Isolation and characterization of mutants corresponding to the MENA, MENB, MENC and MENE enzymatic steps of 5′‐monohydroxyphylloquinone biosynthesis in Chlamydomonas reinhardtii

“…Genomic data for C. reinhardtii (Table ) indicate that the biosynthetic pathway of PhQ from chorismate comprises homologs for nine of the ten consecutive enzymatic steps involved in the biosynthesis of PhQ in Synechocystis sp. PCC 6803 and in A. thaliana (Fatihi et al ., ). We did not find any obvious homolog of the cyanobacterial and plant DHNA–CoA thioesterase in Chlamydomonas or in other green algae (e.g.…”

“…This suggests that in Chlamydomonas , as in Arabidopsis, this part of the biosynthetic pathway also occurs in the peroxisome but this hypothesis remains to be confirmed by subcellular localization experiments. Altogether, our results suggest that localization of the steps involved in the PhQ biosynthesis pathway in Chlamydomonas (Figure ) might be very similar to that previously described in land plants (Fatihi et al ., ), and that there is no alternative route for PhQ synthesis in Chlamydomonas . We thus propose that chorismate is converted into o ‐succinylbenzoate by the first four enzymatic steps (PHYLLO) in the chloroplast.…”

“…In contrast, the Arabidopsis menG-homologous deficient mutant is viable because, as in Synechocystis, demethylphylloquinone acts as substitute for PhQ in PSI (Lohmann et al, 2006). In 2015 it was established in Synechocystis and Arabidopsis that the biosynthesis of PhQ has an additional step: the reduction of the demethylphylloquinone ring by a type-II NADPH dehydrogenase, called NdbB in Synechocystis and NDC1 in Arabidopsis, prior to its trans-methylation by MenG (Fatihi et al, 2015). Synechocystis ndbB and Arabidopsis ndc1 mutants display increased photosensitivity to high light like the PhQ-deficient mutants previously characterized in these organisms.…”

Role of Type 2 NAD(P)H Dehydrogenase NdbC in Redox Regulation of Carbon Allocation in Synechocystis

“…Regulation by NDH-2s also may be targeted to maintain the redox balance of NAD + /NADH, deduced from the fact that when all three Synechocystis NDH-2s were deleted, reduced NADH was strongly prevailing (Cooley and Vermaas, 2001). In addition, it was shown recently that NdbB is involved in vitamin K 1 biosynthesis (Fatihi et al, 2015).…”

Genetically Programmed Changes in Photosynthetic Cofactor Metabolism in Copper-deficient Chlamydomonas

“…It would be interesting to test whether other stress situations also allow PC-8 accumulation and to distinguish the relevant regulatory mechanisms. In Arabidopsis, PC-8 levels are regulated by the activity of a type II NADPH dehydrogenase C1 (ortholog is NDA5 in Chlamydomonas) (47,48) and a plastid ABC1-like kinase (49).…”