Purification, identification and structural modelling of DPP-IV inhibiting peptides from barbel protein hydrolysate

Inhibition of DPP-IV may improve glycemic control in diabetics by preventing the rapid breakdown and there by prolonging the physiological action of incretin hormones. Barbel muscle protein hydrolysate (BMPH) was noted to exhibit DPP-IV inhibitory activity, with an IC50 value of 1.94mg/mL. It was fractionated into five major fractions (FI-FV) by size exclusion chromatography using a Superdex peptide. The FIII fraction was noted to display the highest inhibitory activity, with an IC50 value of 1.23mg/mL, and was, therefore, further fractionated by RP-HPLC. Four major peptide sub-fractions were selected. The results revealed that the SF4 sub-fraction showed the highest DPP-IV inhibitory activity, with an IC50 value of 0.21mg/mL. This sub-fraction was submitted to RP-HPLC, ESI-MS, and ESI-MS/MS analyses. The findings indicated that SF4 consisted of two peptides (IC50=96μg/mL), namely PP1 and PP2, whose structures were identified as Trp-Ser-Gly (330Da) and Phe-Ser-Asp (349Da), respectively. This is the first report of these sequences from barbel proteins. The structural modelling through docking simulations results with DPP-IV showed that the Trp-Ser-Gly peptide bound to DPP-IV with high affinity. Overall, the results suggested that BMPH can be considered as a promising natural source of DPP-IV inhibitory peptides.