Covalent Interactions of Anthocyanins with Proteins: Activity-Based Protein Profiling of Cyanidin-3-O-glucoside

Anthocyanins are common natural pigments with a variety of physiological activities. Traditional perspectives attribute their molecular mechanism to noncovalent interactions influencing signaling pathways. However, this ignores the nature of its benzopyrylium skeleton, which readily reacts with the electron-rich groups of proteins. Here, we modified cyanidin-3-O-glucoside (C3G) via activity-based protein profiling technology by our previous synthesis route and prepared the covalent binding probe (C3G-Probe) and the noncovalent photoaffinity probe (C3G-Diazirine). The properties of C3G's covalent binding to proteins were also discovered by comparing the labeling of the two probes to the whole HepG2 cell proteome. We further explored its target proteins and enriched pathways in HepG2 and HeLa cells. Western blot analysis further confirmed the covalent binding of C3G to four target proteins: insulin-degrading enzyme, metal cation symporter ZIP14, spermatid perinuclear RNA-binding protein, and Cystatin-B. Pathway analysis showed that covalent targets of C3G were concentrated in metabolic pathways and several ribonucleoprotein complexes that were also coenriched. The results of this study provide new insights into the interaction of the naturally active molecule C3G with proteins.