Assembly of the ligand-binding conformation of Mr 46,000 mannose 6-phosphate-specific receptor takes place before reaching the Golgi complex.
The early steps in the biosynthesis of Mr 46,000 mannose 6-phosphate-specific receptor (MPR 46) have been studied by in vivo labeling of transfected BHK cells. The acquisition of phosphomannan-binding activity was compared with changes in protein structure and posttranslational modifications of MPR 46. Intramolecular disulfide bonds were formed before MPR 46 acquired a ligand-binding conformation. A conformational change that resulted in increased trypsin resistance, formation of highly immunogenic epitopes and assembly to noncovalently linked homodimers was observed almost simultaneously with the acquisition of ligand-binding activity. MPR 46 was shown to acquire ligand-binding activity before N-linked oligosaccharides were processed to complex-type forms. Maturation of the ligand-binding conformation was observed under conditions where transport to the Golgi was blocked by lowering the temperature to 16 degrees C, or by addition of brefeldin A or dinitrophenol to the medium at 37 degrees C. This suggests that receptor maturation and assembly take place before reaching the Golgi complex. The affinity towards phosphomannan-containing ligands was shown to be similar for the high-mannose and complex-glycosylated forms of MPR 46.
Hille
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A
Universität Göttingen, Biochemie II, Federal Republic of Germany.
Waheed
A
A
von Figura
K
K
D000818:Animals; D002460:Cell Line; D006056:Golgi Apparatus / Q000378:metabolism*; D006600:Hexosephosphates / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008351:Mannans / Q000378:metabolism; D008360:Mannosephosphates / Q000378:metabolism*; D008970:Molecular Weight; D011487:Protein Conformation; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D014162:Transfection
D006600:Hexosephosphates; D008024:Ligands; D008351:Mannans; D008360:Mannosephosphates; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; C005437:phosphomannan