Mitochondrial 2-hydroxyglutarate metabolism

• In plants, lysine catabolism is the source of D-2-hydroxyglutarate (D-2HG).
• L-2HG would be formed from 2-ketoglutarate (2KG) in a side reaction of mMDH.
• D- and L-2HG are oxidized to 2KG by mitochondrial stereospecific dehydrogenases.
• L-2HG is oxidized back to 2KG by L-2HGDH in a metabolic repair reaction.
• Disturbed plant mitochondrial 2HG metabolism does not seriously affect development.

2-Hydroxyglutarate (2-HG) is a five-carbon dicarboxylic acid with a hydroxyl group at the alpha position, which forms a stereocenter in this molecule. Although the existence of mitochondrial D- and L-2HG metabolisms has long been known in different eukaryotes, the biosynthetic pathways, especially in plants, have not been completely elucidated. While D-2HG is involved in intermediary metabolism, L-2HG may not have a cellular function but it needs to be recycled through a metabolic repair reaction. Independent of their metabolic origin, D- and L-2HG are oxidized in plant mitochondria to 2-ketoglutarate through the action of two stereospecific enzymes, d- and l-2-hydroxyacid dehydrogenases. While plants are to a large extent unaffected by high cellular concentrations of D-2HG, deficiencies in the metabolism of D- and L-2HG result in fatal disorders in humans. We present current data gathered on plant D- and L-2HG metabolisms and relate it to existing knowledge on 2HG metabolism in other organisms. We focus on the metabolic origin of these compounds, the mitochondrial catabolic steps catalyzed by the stereospecific dehydrogenases, and phylogenetic relationships between different studied 2-hydroxyacid dehydrogenases.