Identification of VAYPQCV, a Gastrointestinally Stable Competitive DPP-IV Inhibitory Peptide from Bitter Leaf (Vernonia amygdalina).

Among hydrolysates generated from bitter leaf (Vernonia amygdalina) proteins using multiple proteases, the thermolysin-derived hydrolysate exhibited the strongest inhibition toward human dipeptidyl peptidase IV (DPP-IV). Bioassay-guided RP-HPLC fractionation coupled with LC-MS/MS analysis yielded five candidate peptides for synthesis and validation, among which the heptapeptide VAYPQCV (VV7) showed the strongest inhibitory activity with an IC50 of 19.8 ± 0.6 µM. Enzyme kinetic analysis demonstrated a classical competitive inhibition mode, with VV7 increasing the apparent Km without markedly affecting Vmax. Molecular docking further suggested that VV7 occupies the catalytic cavity of DPP-IV through interactions with Tyr666 in the S1 pocket and Glu205/Glu206 within the S2 subsite. VV7 also remained structurally intact after two-stage simulated gastrointestinal digestion, indicating resistance to extensive proteolytic degradation under the tested conditions. Collectively, these findings identify VV7 as a stable DPP-IV inhibitory peptide from bitter leaf and provide structural insight into its enzyme-level interaction with DPP-IV.