Coupling between d-3-phosphoglycerate dehydrogenase and d-2-hydroxyglutarate dehydrogenase drives bacterial l-serine synthesis

Abstract

l-Serine biosynthesis, a crucial metabolic process in most domains of life, is initiated byd-3-phosphoglycerate (d-3-PG) dehydrogenation, a thermodynamically unfavorable reaction catalyzed byd-3-PG dehydrogenase (SerA).d-2-Hydroxyglutarate (d-2-HG) is traditionally viewed as an abnormal metabolite associated with cancer and neurometabolic disorders. Here, we reveal that bacterial anabolism and catabolism ofd-2-HG are involved inl-serine biosynthesis inPseudomonas stutzeriA1501 andPseudomonas aeruginosaPAO1. SerA catalyzes the stereospecific reduction of 2-ketoglutarate (2-KG) tod-2-HG, responsible for the major production ofd-2-HG in vivo. SerA combines the energetically favorable reaction ofd-2-HG production to overcome the thermodynamic barrier ofd-3-PG dehydrogenation. We identified a bacteriald-2-HG dehydrogenase (D2HGDH), a flavin adenine dinucleotide (FAD)-dependent enzyme, that convertsd-2-HG back to 2-KG. Electron transfer flavoprotein (ETF) and ETF-ubiquinone oxidoreductase (ETFQO) are also essential ind-2-HG metabolism through their capacity to transfer electrons from D2HGDH. Furthermore, while the mutant with D2HGDH deletion displayed decreased growth, the defect was rescued by addingl-serine, suggesting that the D2HGDH is functionally tied tol-serine synthesis. Substantial flux flows throughd-2-HG, being produced by SerA and removed by D2HGDH, ETF, and ETFQO, maintainingd-2-HG homeostasis. Overall, our results uncover thatd-2-HG–mediated coupling between SerA and D2HGDH drives bacteriall-serine synthesis.