Human small-intestinal apolipoprotein B-48 oligosaccharide chains

Abstract

Hepatic apolipoprotein (apo) B-100 isolated from human plasma is known to contain N-linked oligosaccharides of high-mannose-type and complex-type structures. Sequencing data have revealed that apo B-48 of small-intestinal origin, which represents about 48% of apo B-100 polypeptide from the N-terminus, possesses six potential sites for N-linked oligosaccharides, of which five are likely to be glycosylated. The characterization of the carbohydrate moiety of apo B-48 is the focus of this study. Apo B-48 was labelled with L-[35S]methionine and D-[3H]glucosamine in organ culture of human small-intestinal explants. N-Glycanase treatment resulted in loss of radioactivity from D-[3H]glucosamine-labelled but not L-[35S]methionine-labelled apo B-48 secreted into the medium, and caused no distinct change in mobility of apo B-48 upon electrophoresis on 5% polyacrylamide gel. Analysis of monosaccharide content revealed the presence of 16.8, 17.8, 13.4, 3.4, 2.4 and 2.3 residues of N-acetylglucosamine, mannose, galactose, fucose, xylose and N-acetylgalactosamine respectively. Small-intestinal apo B-48 from human lymph chylomicrons bound to [14C]concanavalin A, and the binding could be inhibited with methyl alpha-D-mannoside. In addition, wheat-germ, peanut, Limulus, soya-bean and Ulex lectins bound apo B-48 specifically. To characterize the carbohydrate moiety further, N-linked oligosaccharides were released by N-Glycanase treatment and reduced with NaB3H4. Labelled oligosaccharides were separated on a concanavalin A-Sepharose column. The majority (78%) were biantennary complex-type structures, 16% were high-mannose type and 6% (not retained by the column) most probably represented higher-branched oligosaccharides. These results suggest the presence of one high-mannose-type and four biantennary complex-type oligosaccharides, as well as probable O-linked sugars in apo B-48. By the use of h.p.l.c., exoglycosidase treatments and ion-exchange chromatography, a mixture of high-mannose-type species with predominant Man8GlcNAc2 as well as monosialylated, desialylated and fucosylated forms of complex-type oligosaccharides were detected.

Erythrocyte-Bound Apolipoprotein B in Relation to Atherosclerosis, Serum Lipids and ABO Blood Group

“…Studies are underway in our laboratory to gain more insight in the relationship between blood groups and ery-apoB. It is tempting to speculate that different carbohydrate groups on the apo B molecule interact with fucose, galactose, N acetyl-galactosamine or N acetyle-glucosamine, which make up the A, B and H antigens [16].…”

Differentiation of Intrahepatic Membrane-Bound and Secretory Apolipoprotein B by Monoclonal Antibodies: Membrane-Bound Apolipoprotein B Is More Glycosylated

“…Most, if not all, of the secondary, tertiary, or quaternary structure of apoB would have been destroyed under these conditions. Similarly, the experiments to deglycosylate apoB were all performed in the presence of ionic (SDS) and nonionic (NP-40) detergents before electrophoresis, blotting, and antibody probing (Figure 6)-Human apoB is both N-glycosylated and O-glycosylated (Taniguchi et al, 1989;Sasak et al, 1991). No data are available concerning the glycosylation of rat apoB.…”

The known unknowns of apolipoprotein glycosylation in health and disease

“…Tri-antennary, bi-antennary with sialylated LacdiNAc, hybrid, truncated complex bi-antennary and high mannose type (Man 5–9) ( Figure 1 ) structures make up the remainder ( Garner et al., 2001a ; Harazono et al., 2005 ; Sukhorukov et al., 2019 ). In ApoB-48, five out of six predicted N -glycosylation sites are glycosylated and contain sialylated complex bi-antennary type (78%) and high mannose type structures ( Sasak et al., 1991 ).…”