THE SACCHARIDE CHAIN OF LUPIN SEED CONGLUTIN-GAMMA IS NOT RESPONSIBLE FOR THE PROTECTION OF THE NATIVE PROTEIN FROM DEGRADATION BY TRYPSIN, BUT FACILITATES THE REFOLDING OF THE ACID-TREATED PROTEIN TO THE RESISTANT CONFORMATION

Native glycosylated and enzymically deglycosylated conglutin gamma (a lupin seed oligomeric protein) both showed an unusual resistance to tryptic degradation. The result of this treatment was that a single 40-residue peptide was cleaved from the N-terminus of conglutin gamma light subunit. Acid treatment of the two protein forms led to their substantial unfolding, as indicated by CD spectra. After this treatment, both polypeptides were completely degraded by trypsin after a few minutes of incubation. Conversely, trypsin pulse experiments run under renaturing conditions demonstrated a different refolding behaviour of the two proteins: the glycosylated form became resistant to trypsin after a 7-h renaturation, while the deglycosylated form required 42 h renaturation. These results were confirmed by CD spectra and reverse-phase HPLC analyses of the glycosylated and deglycosylated conglutin gamma forms. Therefore, it was concluded that the saccharide chain of conglutin gamma increased the rate of formation of a trypsin-resistant conformation upon refolding of the acid-treated protein, without playing any direct role in the protection of the native protein from proteolysis.