Résumé
Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is a crucial reducing cofactor for reductive biosynthesis and protection from oxidative stress. To fulfill their heightened anabolic and reductive power demands, cancer cells must boost their NADPH production. Pro-growth and mitogenic protein kinases promote the activity of cytosolic NAD kinase (NADK), which produces NADP + , a limiting NADPH precursor. However, the molecular architecture and mechanistic regulation of human NADK remain undescribed. Here, we report the cryo-EM structure of human NADK, both in its apo-form and in complex with its substrate NAD + , revealing a tetrameric organization with distinct structural features. We discover that the N-terminal and C-terminal tails of NADK have opposing effects on its enzymatic activity and cellular NADP(H) levels. Specifically, the C-terminal region is critical for NADK activity, whereas the N-terminal region exhibits an inhibitory role. This study reveals new molecular insights into the regulation of a vital enzyme governing NADP(H) production.