D-Lactate dehydrogenase links methylglyoxal degradation and electron 13 transport through cytochrome C

WELCHEN E; SCHMITZ J; FUCHS P; GARCÍA L; WAGNER S; WIENSTROER J; SCHERTL P; BRAUN HP; SCHWARZLÄNDER M; GONZALEZ DH; MAURINO VG

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Lugar: Rockville; Año: 2016

0032-0889

Glycolysis generates methylglyoxal (MG) as an unavoidable, cytotoxic by-product in plant cells. MG generation can rise strongly under stress, making effective detoxification essential. MG scavenging can be performed by the glyoxalase system, which produces D-lactate as an intermediate. D-lactate dehydrogenase of Arabidopsis (D-LDH; At5g06580) catalyses in vitro the oxidation of D-lactate to pyruvate using FAD as cofactor, but its function in the context of the plant cell has been insufficiently understood. Blue native polyacrylamide electrophoresis of mitochondrial extracts combined with in gel activity assays using different substrates and tandem mass spectrometry allowed us to definitely show that D-LDH is specific for D-lactate. D-LDH was found in active dimers and did not associate with the respiratory supercomplexes of the inner mitochondrial membrane. Arabidopsis plants defective in cytochrome c (CYTc) provided genetic evidence that CYTc acts as the in vivo electron acceptor of D-LDH. The CYTc mutants, like D-LDH mutants, were more sensitive to D-lactate and MG, suggesting that they function in the same pathway. In addition, overexpression of D-LDH and CYTc increased tolerance to both compounds in a manner that was dependent on the amount of the other protein. Together with fluorescent fine-localization of D-LDH, the functional interaction with CYTc in vivo strongly suggests that D-lactate oxidation takes place in the mitochondrial intermembrane space delivering electrons to the respiratory chain through CYTc. These results provide a comprehensive picture of the organisation and function of D-LDH in the plant cell and exemplify how the plant mitochondrial respiratory chain functions as a multi-functional electron sink for reductants from cytosolic pathways.