Exploration of novel DPP-IV inhibitory peptides from discarded eggshell membrane: An integrated in silico and in vitro study

Dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides exhibit great potential to alleviate type II diabetes. This study aimed to prepare, identify and explore the molecular mechanism of DPP-IV inhibitory peptides from eggshell membrane (ESM), an abundant byproduct of the food industry, based on combining in silico and in vitro assessments. In silico evaluation of ten major ESM proteins revealed the great potential of ESM as a novel source of DPP-IV inhibitors. Moreover, the optimal combined-enzymatic strategy (alkaline protease + papain) for the efficient production of DPP-IV inhibitory peptides from ESM was designed by simulated proteolysis. Corresponding with in silico predictions, in vitro assessments confirmed that sodium sulfite assisted the screened dual enzymes led to better production of DPP-IV inhibitory peptides from ESM, with preferable total nitrogen recovery (86.61% ± 4.83%), DPP-IV inhibitory activity (64.61% ± 2.75%) and total antioxidant activity (215.27 ± 1.75 μg/mL). Due to the correlation between diabetes and oxidative stress, the antioxidant and DPP-IV inhibitory activities of the hydrolysate facilitate its amelioration of diabetes. Three novel DPP-IV inhibitory peptides with high abundance in ESM hydrolysates (YPEPPPQ, HDGADVS and VTDGQPH) were identified by LC-MS/MS, in silico characterization and molecular docking. These peptides were synthesized and confirmed to possess DPP-IV inhibitory activity, potentially relating to their stable binding with key residues within the S1, S2 pockets and catalytic triad of DPP-IV via hydrogen bonding and hydrophobic interaction. Overall, this research suggests an effective and time-saving strategy to investigate novel DPP-IV inhibitory peptides from ESM, as well as opens new opportunities for ESM application in antidiabetic foods.