A pathway for repair of NAD(P)H in plants.
Unwanted enzyme side reactions and spontaneous decomposition of metabolites can lead to a build-up of compounds that compete with natural enzyme substrates and must be dealt with for efficient metabolism. It has recently been realized that there are enzymes that process such compounds, formulating the concept of metabolite repair. NADH and NADPH are vital cellular redox cofactors but can form non-functional hydrates (named NAD(P)HX) spontaneously or enzymatically that compete with enzymes dependent on NAD(P)H, impairing normal enzyme function. Here we report on the functional characterization of components of a potential NAD(P)H repair pathway in plants comprising a stereospecific dehydratase (NNRD) and an epimerase (NNRE), the latter being fused to a vitamin B6 salvage enzyme. Through the use of the recombinant proteins, we show that the ATP-dependent NNRD and NNRE act concomitantly to restore NAD(P)HX to NAD(P)H. NNRD behaves as a tetramer and NNRE as a dimer, but the proteins do not physically interact. In vivo fluorescence analysis demonstrates that the proteins are localized to mitochondria and/or plastids, implicating these as the key organelles where this repair is required. Expression analysis indicates that whereas NNRE is present ubiquitously, NNRD is restricted to seeds but appears to be dispensable during the normal Arabidopsis life cycle.
From the Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland.
Maite
M
Colinas
From the Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland.
Holly V
HV
Shaw
From the Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland.
Sylvain
S
Loubéry
From the Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland.
Markus
M
Kaufmann
From the Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland.
Michael
M
Moulin
From the Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland theresa.fitzpatrick@unige.ch.
Teresa B
TB
Fitzpatrick
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D018506:Gene Expression Regulation, Plant; D006836:Hydro-Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D053858:Metabolic Networks and Pathways / Q000235:genetics; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D009243:NAD / Q000737:chemistry / Q000378:metabolism*; D009249:NADP / Q000737:chemistry / Q000378:metabolism*; D030821:Plants, Genetically Modified; D018087:Plastids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D019998:Racemases and Epimerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; D008164:Luminescent Proteins; D009243:NAD; D009249:NADP; D006836:Hydro-Lyases; D019998:Racemases and Epimerases
Arabidopsis; Dehydratase; Enzyme Catalysis; Epimerase; Fluorescence; Metabolism; Metabolite Repair; Mitochondria; NAD(P)H; Protein Localization