Identification and Characterization of a Pepsin and Chymotrypsin-Resistant Peptide in the α Subunit of the 11S Globulin Legumin from Common Bean (Phaseolus vulgaris L.)

The 11S globulin legumin typically accounts for approximately 3% of total protein in common bean (Phaseolus vulgaris). It was previously reported that a legumin peptide of approximately 20 kDa is resistant to pepsin digestion. Sequence prediction suggested that the pepsin resistant peptide is located at the C-terminal end of the α-subunit, within a glutamic acid-rich domain, overlapping with a chymotrypsin-resistant peptide. Using purified legumin, the peptide of ca. 20 kDa was found to be resistant to pepsin digestion in a pH-dependent manner, and its location was determined by two-dimensional gel electrophoresis and LC-MS-MS. Sample 1 corresponds to trypsin spot. Sample 2 corresponds to legumin alpha subunit spot of 63 kDa. Sample 3 corresponds to legumin alpha subunit spot of 48 kDa. Sample 4 corresponds to legumin beta subunit spot. Sample 5 corresponds to pepsin resistant spot of alpha subunit.