Fig. 1.

The coupling between SerA and D2HGDH makes the robust interconversion between d-2-HG and 2-KG (green dotted box) to overcome the thermodynamic barrier of d-3-PG dehydrogenation and facilitate the biosynthetic process of l-serine (purple pathway). The coupling establishes a linkage among the intermediates of glycolysis (d-3-PG), TCA cycle (2-KG), and l-serine biosynthesis. The black dotted box indicates the already known straightforward connections between the intermediates of glycolysis (PEP and pyruvate) and TCA cycle (OAA). OAA, oxaloacetate; PEP, phosphoenolpyruvate; 3-PHP, 3-phosphohydroxypyruvate.