Flavonoids as Protein Disulfide Isomerase Inhibitors: Key Molecular and Structural Features for the Interaction

Quercetin-3-rutinoside (rutin) is a bioflavonoid that is common in foods. Thefinding that quercetin-3-rutinosideinhibits protein disulfide isomerase (PDI) and potently blocks thrombosisin vivohas enabled the evaluation of PDI inhibition inmultiple animal models of thrombus formation and has prompted clinical studies of PDI inhibition in thrombosis. Nonetheless, howquercetin-3-rutinoside blocks PDI activity remains an unanswered question. Combining NMR spectroscopy, site-directedmutagenesis, and biological assays, we identified H256 as the key residue for PDI interacting with quercetin-3-rutinoside. Quercetin-3-rutinoside inhibited the activity of PDI (WT) but not PDI (H256A). Molecular dynamic simulations indicated that theflavonoidskeleton, but not the rutinoside conjugate, is embedded in the major binding pocket on the b ' domain. Among several quercetin-3-rutinoside analogues tested, only compounds with a phenoxyl group at position 7 showed direct binding to PDI, further supportingour molecular model. Studies using purified coagulation factors showed that quercetin-3-rutinoside inhibited the augmenting effectsof PDI (WT), but not PDI (H256A), on tissue factor (TF) activity. Quercetin-3-rutinoside also inhibited chemotherapy-induced TFactivity enhancement on endothelial cells. Together, our studies show that residue H256 in PDI and the phenoxyl group at position7 in quercetin-3-rutinoside are essential for inhibition of PDI by quercetin-3-rutinoside. These results provide new insight into themolecular mechanism by whichflavonoids block PDI activity

Automated summary

This study identified H256 as the key residue for the interaction between quercetin-3-rutinoside and protein disulfide isomerase (PDI). The results also showed that the flavonoid skeleton, but not the rutinoside conjugate, is embedded in the major binding pocket of PDI. In addition, the inhibition of PDI activity by quercetin-3-rutinoside is dependent on the phenoxyl group at position 7. These findings provide new insights into the molecular mechanism of PDI inhibition by flavonoids.