DIRECT DEMONSTRATION OF THE ESSENTIAL ROLE OF THE INTRAMOLECULAR HIGH-MANNOSE OLIGOSACCHARIDE CHAINS IN THE FOLDING AND ASSEMBLY OF SOYBEAN (GLYCINE-MAX) LECTIN POLYPEPTIDES

We investigated the role of the intramolecular high-mannose oligosaccharide chains in the folding and assembly of soybean lectin polypeptides. Soybean lectin, dissociated into subunits and completely denatured in 6 M guanidine hydrochloride, was quantitatively reconstituted to the active tetrameric structure by simple dilution. However, neither the activity nor the tetrameric structure was regained in the presence of 100 muM of an asparagine-linked oligosaccharide, Man9GlcNAc2Asn, having the same structure as that of the sugar chains of soybean lectin. Besides, the same concentration of this glycopeptide even dissociated, although only gradually, the native lectin into subunits. On the other hand, the deglycosylated subunits had no ability to regain the activity or the tetrameric structure. The present study provided for the first time direct evidence of the essential role of the intramolecular high-mannose oligosaccharide chains in the proper folding and assembly of glycopolypeptides.