N-Glycans protect proteins from protease digestion through their binding affinities for aromatic amino acid residues.
It was previously revealed [Yamaguchi, H., Nishiyama, T., and Uchida, M. (1999) J. Biochem. 126, 261-265] that N-glycans of both the high-mannose and complex types have binding affinity for aromatic amino acid residues. This study shows that free N-glycans protect proteins from protease digestion through their binding affinities for the aromatic amino acid residues exposed on protein molecules. Protease digestion of bovine pancreatic RNase A and bovine a-lactalbumin was depressed in solutions (1 mM or so) of free N-glycans of both the high-mannose and complex types. The increasing order of the protective effects of the N-glycans paralleled that of their affinities for aromatic amino acid residues; and the presence of aromatic amino acids practically abolished the protective effects of the N-glycans. The N-glycans also depressed the protease digestion of metallothionein, an aromatic amino acid-free protein, in agreement with the observation that the N-glycans also interact with the solvent-exposed aromatic amino acid residues of the proteases. Thus it seems probable that the N-glycans protect proteins from protease digestion by steric hindrance attributable to their binding affinity for the solvent-exposed aromatic amino acid residues of both substrate proteins and proteases.
Nishiyama
T
T
Department of Applied Biological Chemistry, College of Agriculture, Osaka Prefecture University, Gakuen-cho Sakai, Osaka 599-8531, Japan.
Kimura
N
N
Jitsuhara
Y
Y
Uchida
M
M
Ochi
F
F
Yamaguchi
H
H
D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D050260:Carbohydrate Metabolism; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D002918:Chymotrypsin / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D007768:Lactalbumin / Q000378:metabolism; D008668:Metallothionein / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry* / Q000502:physiology*; D011485:Protein Binding; D012259:Ribonuclease, Pancreatic / Q000378:metabolism; D013997:Time Factors; D014357:Trypsin / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D000596:Amino Acids; D011134:Polysaccharides; D014443:Tyrosine; D007768:Lactalbumin; D008668:Metallothionein; C025787:N-acetyltyrosine; D012259:Ribonuclease, Pancreatic; D010450:Endopeptidases; D002918:Chymotrypsin; D014357:Trypsin