Bioorthogonal Vitamin C Probes Enable Cellular Profiling and Investigation of Lysine Vitcylation.

Vitamin C is an essential micronutrient, yet its direct chemical engagement with the proteome remains poorly defined. Here, we develop and experimentally benchmark a bioorthogonal probe platform for labeling, profiling, and imaging of lysine vitcylation, a recently identified vitamin C-derived post-translational modification, in living cells. Chemoproteomic analysis and fluorescence imaging reveal a candidate vitcylome enriched in nucleolar proteins associated with ribonucleoprotein biogenesis and RNA processing, and reporter-derived lysine adducts on selected targets were validated by mass spectrometry. Time-resolved analyses demonstrate that intracellular vitcylation undergoes unexpectedly rapid remodeling, indicating active cellular regulation. Furthermore, a genome-wide CRISPR-Cas9 screen identifies glutathione S-transferase P1 (GSTP1) as an upstream regulator of global vitamin C-derived protein modification, linking vitcylation remodeling to cellular electrophile handling and redox homeostasis. Collectively, this platform provides a chemical framework for profiling, visualizing, and investigating protein vitcylation in living cells, and reveals vitcylation as a dynamic, spatially organized and regulated metabolic modification.