title: Isolation and characterization of the two glycosylation isoforms of low molecular weight mannose 6-phosphate receptor from bovine testis. Effect of carbohydrate components on ligand binding.
abstract: Low molecular weight mannose 6-phosphate receptor from bovine testis exhibits two isoforms on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Mr values of 45,000 (MPR-2A) and 41,000 (MPR-2B), respectively. Each isoform was purified to near homogeneity by the sequential application of differential centrifugation and affinity chromatography. The isoforms contain a common polypeptide core, but differ in their carbohydrate content. Treatment with specific endoglycosidases demonstrated that each isoform contains two high mannose and/or hybrid and two complex N-linked oligosaccharide chains. The results obtained from treatment of each isoform with endo-beta-galactosidase and neuraminidases and from lectin affinity chromatography reveal that MPR-2A contains a linear polylactosamine sequence(s) comprised of approximately 5 lactosamine units. A majority of the outer branches of the complex chains associated with MPR-2A are terminated with sialic acid residues. In contrast, MPR-2B lacks a polylactosamine sequence and a majority of the outer branches of the complex chains are terminated with galactose residues. MPR-2A exhibited a lower affinity than MPR-2B for mannose 6-phosphate-containing ligands. Treatment of MPR-2A with endo-beta-galactosidase and/or neuraminidases followed by affinity chromatography revealed that polylactosamine and sialic acid residues impair the ability of MPR-2A to bind ligands.
authors.affiliation: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor 48109.
authors.forename: M M
authors.initials: MM
authors.lastname: Li
authors.forename: G W
authors.initials: GW
authors.lastname: Jourdian
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000606:Amino Sugars / Q000737:chemistry; D000818:Animals; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000032:analysis / Q000737:chemistry; D002417:Cattle; D002498:Centrifugation; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D006031:Glycosylation; D037102:Lectins; D008024:Ligands; D008297:Male; D008360:Mannosephosphates / Q000378:metabolism*; D051379:Mice; D008970:Molecular Weight; D011134:Polysaccharides / Q000737:chemistry; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D012794:Sialic Acids / Q000737:chemistry; D013737:Testis / Q000378:metabolism*; D000519:alpha-Galactosidase / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000606:Amino Sugars; D002241:Carbohydrates; D037102:Lectins; D008024:Ligands; D008360:Mannosephosphates; D011134:Polysaccharides; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D012794:Sialic Acids; C066929:polylactosamine; D000519:alpha-Galactosidase