Ca2+-binding and Ca2+-independent respiratory NADH and NADPH dehydrogenases of Arabidopsis thaliana.
Type II NAD(P)H:quinone oxidoreductases are single polypeptide proteins widespread in the living world. They bypass the first site of respiratory energy conservation, constituted by the type I NADH dehydrogenases. To investigate substrate specificities and Ca(2+) binding properties of seven predicted type II NAD(P)H dehydrogenases of Arabidopsis thaliana we have produced them as T7-tagged fusion proteins in Escherichia coli. The NDB1 and NDB2 enzymes were found to bind Ca(2+), and a single amino acid substitution in the EF hand motif of NDB1 abolished the Ca(2+) binding. NDB2 and NDB4 functionally complemented an E. coli mutant deficient in endogenous type I and type II NADH dehydrogenases. This demonstrates that these two plant enzymes can substitute for the NADH dehydrogenases in the bacterial respiratory chain. Three NDB-type enzymes displayed distinct catalytic profiles with substrate specificities and Ca(2+) stimulation being considerably affected by changes in pH and substrate concentrations. Under physiologically relevant conditions, the NDB1 fusion protein acted as a Ca(2+)-dependent NADPH dehydrogenase. NDB2 and NDB4 fusion proteins were NADH-specific, and NDB2 was stimulated by Ca(2+). The observed activity profiles of the NDB-type enzymes provide a fundament for understanding the mitochondrial system for direct oxidation of cytosolic NAD(P)H in plants. Our findings also suggest different modes of regulation and metabolic roles for the analyzed A. thaliana enzymes.
Department of Cell and Organism Biology, Lund University, Sölvegatan 35B, SE-223 62 Lund, Sweden.
Daniela A
DA
Geisler
Department of Cell and Organism Biology, Lund University, Sölvegatan 35B, SE-223 62 Lund, Sweden.
Christian
C
Broselid
Department of Cell and Organism Biology, Lund University, Sölvegatan 35B, SE-223 62 Lund, Sweden.
Lars
L
Hederstedt
Department of Cell and Organism Biology, Lund University, Sölvegatan 35B, SE-223 62 Lund, Sweden. Electronic address: Allan.Rasmusson@cob.lu.se.
Allan G
AG
Rasmusson
D020816:Amino Acid Motifs / Q000235:genetics; D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004579:Electron Transport / Q000502:physiology; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D008928:Mitochondria / Q000201:enzymology / Q000235:genetics; D009249:NADP / Q000378:metabolism; D009252:NADPH Dehydrogenase; D010084:Oxidation-Reduction; D011485:Protein Binding / Q000235:genetics; D011993:Recombinant Fusion Proteins
D029681:Arabidopsis Proteins; D002135:Calcium-Binding Proteins; D011993:Recombinant Fusion Proteins; D009249:NADP; D009252:NADPH Dehydrogenase; D002118:Calcium