Purification and a molecular docking study of α-glucosidase-inhibitory peptides from a soybean protein hydrolysate with ultrasonic pretreatment

Soybean protein was hydrolyzed using trypsin with ultrasound pretreatment to obtain a soybean protein hydrolysate. The latter was separated sequentially by ultrafiltration, ion exchange chromatography, gel filtration chromatography, and reversed-phase high-performance liquid chromatography. A highly active component with molecular weight less than 5 kDa, obtained by ultrafiltration, significantly reduced the levels of fasting blood glucose in mice. α-Glucosidase-inhibitory activity of fraction C-III-2a separated by reversed-phase high-performance liquid chromatography was the highest, and the half-inhibitory concentration (IC50) was 0.049 mg/mL. Amino acid sequences of two tripeptides from fraction C-III-2a were identified as Gly-Ser-Arg and Glu-Ala-Lys by ion trap tandem mass spectrometry. Molecular docking analyses revealed that the α-glucosidase inhibition by the peptides could be mainly attributed to the formation of five strong hydrogen bonds between Glu-Ala-Lys and His-674, Asp-518, Arg-600, Asp-616, and Asp-282 in α-glucosidase, and to four hydrogen bonds between Gly-Ser-Arg and residues Asp-282, Asp-518, and Asp-616. The results indicated that an α-glucosidase-inhibitory peptide may have hypoglycemic efficacy when used as an ingredient in novel functional foods.