title: 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.
authors.affiliation: Department of Pediatrics, New England Medical Center, Tufts University School of Medicine, Boston, MA 02111.
authors.forename: W V
authors.initials: WV
authors.lastname: Sasak
authors.forename: J S
authors.initials: JS
authors.lastname: Lown
authors.forename: K A
authors.initials: KA
authors.lastname: Colburn
mesh_terms: D053283:Apolipoprotein B-48; D001055:Apolipoproteins B / Q000096:biosynthesis* / Q000302:isolation & purification; D002240:Carbohydrate Sequence; D002846:Chromatography, Affinity; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D006801:Humans; D007583:Jejunum / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000378:metabolism; D009844:Oligosaccharides / Q000302:isolation & purification*; D009924:Organ Culture Techniques; D013462:Sulfur Radioisotopes
chemical_list: D053283:Apolipoprotein B-48; D001055:Apolipoproteins B; D009844:Oligosaccharides; D013462:Sulfur Radioisotopes; D008715:Methionine