THE SACCHARIDE CHAIN OF LUPIN SEED CONGLUTIN-GAMMA IS NOT RESPONSIBLEFOR 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 tr yptic degradation. The result of this treatment was that a single 40-r esidue peptide was cleaved from the N-terminus of conglutin gamma ligh t subunit. Acid treatment of the two protein forms led to their substa ntial unfolding, as indicated by CD spectra. After this treatment, bot h polypeptides were completely degraded by trypsin after a few minutes of incubation. Conversely, trypsin pulse experiments run under renatu ring conditions demonstrated a different refolding behaviour of the tw o proteins: the glycosylated form became resistant to trypsin after a 7-h renaturation, while the deglycosylated form required 42 h renatura tion. These results were confirmed by CD spectra and reverse-phase HPL C analyses of the glycosylated and deglycosylated conglutin gamma form s. Therefore, it was concluded that the saccharide chain of conglutin gamma increased the rate of formation of a trypsin-resistant conformat ion upon refolding of the acid-treated protein, without playing any di rect role in the protection of the native protein from proteolysis.