Promotion of polypeptide folding by interactions with Asn-Glycans

We have recently revealed that the intramolecular Asn-glycans promote the refolding of reductively denatured bovine pancreatic RNase B, and that extramolecular Asn-glycans of both high-mannose and complex types also markedly stimulate the oxidative refolding of RNase B and its nonglycosylated form, RNase A [Yamaguchi, H. and Uchida, M. (1996) J. Biochem. 120, 474-477; Nishimura et al. (1998) J. Biochem. 123, 516-520]. The present investigation was undertaken to see whether this function of Asn-glycans is specific to the refolding of pancreatic RNases; i.e., extramolecular Asn-glycans were examined for their effects on the oxidative refolding of hen egg white lysozyme and bovine alpha-lactalbumin by monitoring changes in activity, dynamic volume, intrinsic fluorescence, and affinity for a fluorescent probe, 1-anilino-8-naphthalenesulfonate. Asn-glycans of both high-mannose and complex types markedly stimulated the oxidative refolding of these proteins, giving similar results to those previously obtained with RNases, though differences attributable to the characteristics of individual proteins were observed in the promotive effects. Thus it seems probable that Asn-glycans generally promote the proper folding of denatured polypeptides.