Structural heterogeneity of sugar chains in immunoglobulin G. Conformation of immunoglobulin G molecule and substrate specificities of glycosyltransferases.
The heterogeneous asparagine-linked sugar chains of bovine and human immunoglobulins G were separated into 12 components by reversed-phase high performance liquid chromatography, and their structures were determined by 1H NMR spectroscopy. Both immunoglobulin (Ig) G sources contained eight non-bisected biantennary complexes and four bisected biantennary complexes. In the non-bisected sugar chains of bovine IgG, galactosylation of the Man alpha 1-3 branch predominated over that of the Man alpha 1-6, whereas in the bisected complexes galactosylation of the Man alpha 1-6 branch predominated. This difference can be explained by the substrate specificities of the galactosyl-transferases and of the N-acetylglucosaminyltransferase III involved in their synthesis. The sugar chains of human IgG1 differs in the distribution of its galactose residues from bovine IgG and human IgG2. The Man alpha 1-6 branch of all IgG1s was more highly galactosylated than the Man alpha 1-3 branch even in the non-bisected complexes. Such findings are in conflict with the substrate specificities of galactosyltransferases. Whereas these enzymes derivatized more of the Man alpha 1-6 branch of native human IgG1, in denatured protein more of the Man alpha 1-3 branch was galactosylated. Thus, protein conformation may influence the structure of its sugar chains.
Fujii
S
S
Department of Biochemistry, Osaka University Medical School, Japan.
Nishiura
T
T
Nishikawa
A
A
Miura
R
R
Taniguchi
N
N
D000818:Animals; D001216:Asparagine; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D005700:Galactosyltransferases / Q000378:metabolism*; D005964:Glucosyltransferases / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D007074:Immunoglobulin G / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009101:Multiple Myeloma / Q000276:immunology; D017351:N-Acetylglucosaminyltransferases; D009844:Oligosaccharides / Q000096:biosynthesis* / Q000302:isolation & purification; D011499:Protein Processing, Post-Translational; D012016:Reference Values; D013379:Substrate Specificity
D007074:Immunoglobulin G; D009844:Oligosaccharides; D001216:Asparagine; D005700:Galactosyltransferases; D005964:Glucosyltransferases; D017351:N-Acetylglucosaminyltransferases; C037649:N-acetyllactosaminide beta-1,6-N-acetylglucosaminyltransferase