Two D-2-hydroxy-acid dehydrogenases in arabidopsis thaliana with catalytic capacities to participate in the last reactions of the methylglyoxal and β-oxidation pathways
Artikel i vetenskaplig tidskrift, 2009
The Arabidopsis thaliana locus At5g06580 encodes an ortholog to Saccharomyces cerevisiae D-lactate dehydrogenase (AtD-LDH). The recombinant protein is a homodimer of 59-kDa subunits with one FAD per monomer. A substrate screen indicated that AtD-LDH catalyzes the oxidation of D- and L-lactate, D-2-hydroxybutyrate, glycerate, and glycolate using cytochrome c as an electron acceptor. AtD-LDH shows a clear preference for D-lactate, with a catalytic efficiency 200- and 2000-fold higher than that for L-lactate and glycolate, respectively, and a Km value for D-lactate of ∼160 μM. Knock-out mutants showed impaired growth in the presence of D-lactate or methylglyoxal. Collectively, the data indicated that the protein is a D-LDH that participates in planta in the methylglyoxal pathway. Web-based bioinformatic tools revealed the existence of a paralogous protein encoded by locus At4g36400. The recombinant protein is a homodimer of 61-kDa subunits with one FAD per monomer. A substrate screening revealed highly specific D-2-hydroxyglutarate (D-2HG) conversion in the presence of an organic cofactor with a Km value of ∼580 μM. Thus, the enzyme was characterized as a D-2HG dehydrogenase (AtD-2HGDH). Analysis of knock-out mutants demonstrated that AtD-2HGDH is responsible for the total D-2HGDH activity present in A. thaliana. Gene coexpression analysis indicated that AtD-2HGDH is in the same network as several genes involved in β-oxidation and degradation of branched-chain amino acids and chlorophyll. It is proposed that AtD-2HGDH participates in the catabolism of D-2HG most probably during the mobilization of alternative substrates from proteolysis and/or lipid degradation.