Post‐translational regulation of human D‐3‐phosphoglycerate dehydrogenase in Alzheimer's disease

Emerging evidence suggests that sex-specific differences in L-serine (L-Ser) metabolism play a key role in Alzheimer's disease (AD). While disruptions in amino acid balance are well known, recent findings point to a dimorphic regulation of the serine biosynthetic pathway. To explore this, we examined post-translational modifications (PTMs) of D-3-phosphoglycerate dehydrogenase (PHGDH)-the rate-limiting enzyme for de novo L-Ser synthesis-as a potentialmechanism underlying this difference. PHGDH was immunoprecipitated from hippocampal tissue of healthy and AD-affected males and females and analyzed by mass spectrometry. Five phosphorylation sites (S55, T60, T78, S383, and S473) were shared across all groups, but a unique deacetylation at K289 appeared exclusively in AD males. Functional assays using recombinant PHGDH variants revealed that changes at solvent-exposed sites (K289, S383, and S473) reduced solubility, while phosphomimetic substitutions at S55 and T78 within the catalytic cleft strongly impaired activity. Notably, mimicking acetylation at K289 improved protein stability. Overall, these PTMs act both as subtle modulators and as on/off switches, fine-tuning PHGDH function and potentially contributing to sex-dependent metabolic vulnerability in AD.