Inducible NAD(H)-linked methylglyoxal oxidoreductase regulates cellular methylglyoxal and pyruvate through enhanced activities of alcohol dehydrogenase and methylglyoxal-oxidizing enzymes in glutathione-depleted Candida albicans

Background: High methylglyoxal content disrupts cell physiology, but mammals have scavengers to prevent glycolytic and mitochondrial dysfunctions. In yeast, methylglyoxal accumulation triggers methylglyoxal-oxidizing alcohol dehydrogenase (Adh1) activity. While methylglyoxal reductases and glyoxalases have been well studied in prokaryotes and eukaryotes, experimental evidence for methylglyoxal dehydrogenase (Mgd) and other catalytic activities of this enzyme affecting glycolysis and the tricarboxylic acid cycle is lacking. Methods: A glycine-rich cytoplasmic Mgd protein, designated as Mgd1/Grp2, was isolated from glutathione-depleted Candida albicans. The effects of Mgdl/Grp2 activities on metabolic pathophysiology were investigated using knockout and overexpression mutants. We measured glutathione-(in)dependent metabolite contents and metabolic effects, including viability, oxygen consumption, ADH1 transcripts, and glutathione reductase and alpha-ketoglutarate dehydrogenase activities in the mutants. Based on the findings, methylglyoxal-oxidizing proteins were monitored to determine effects of MGDI/GRP2 disruption on methylglyoxal-scavenging traits during glutathione deprivation. Results: Methylglyoxal-oxidizing NAD(H)-linked Mgd1/Grp2 was found solely in glutathione auxotrophs, and it catalyzed the reduction of both methylglyoxal and pyruvate. MGDI/GRP2 disruptants showed growth defects, cell-cycle arrest, and methylglyoxal and pyruvate accumulation with mitochondrial impairment, regardless of ADH1 compensation. Other methylglyoxal-oxidizing enzymes were identified as key glycolytic enzymes with enhanced activity and transcription in MGDI/GRP2 disruptants, irrespective of glutathione content. Conclusions: Failure of methylglyoxal and pyruvate dissimilation by Mgdl/Grp2 deficiency leads to poor glutathione-dependent redox regulation despite compensation by Adh1. General significance: This is the first report that multifunctional Mgd activities contribute to scavenging methylglyoxal and pyruvate to maintain metabolic homeostasis and the redox pool via glycolytic enzymes and Adh1 expression.