title: ER/Golgi intermediates acquire Golgi enzymes by brefeldin A-sensitive retrograde transport in vitro.
abstract: Secretory proteins exit the ER in transport vesicles that fuse to form vesicular tubular clusters (VTCs) which move along microtubule tracks to the Golgi apparatus. Using the well-characterized in vitro approach to study the properties of Golgi membranes, we determined whether the Golgi enzyme NAGT I is transported to ER/Golgi intermediates. Secretory cargo was arrested at distinct steps of the secretory pathway of a glycosylation mutant cell line, and in vitro complementation of the glycosylation defect was determined. Complementation yield increased after ER exit of secretory cargo and was optimal when transport was blocked at an ER/Golgi intermediate step. The rapid drop of the complementation yield as secretory cargo progresses into the stack suggests that Golgi enzymes are preferentially targeted to ER/Golgi intermediates and not to membranes of the Golgi stack. Two mechanisms for in vitro complementation could be distinguished due to their different sensitivities to brefeldin A (BFA). Transport occurred either by direct fusion of preexisting transport intermediates with ER/Golgi intermediates, or it occurred as a BFA-sensitive and most likely COP I-mediated step. Direct fusion of ER/Golgi intermediates with cisternal membranes of the Golgi stack was not observed under these conditions.
authors.affiliation: Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Lin
authors.forename: H D
authors.initials: HD
authors.lastname: Love
authors.forename: J N
authors.initials: JN
authors.lastname: Gushue
authors.forename: J J
authors.initials: JJ
authors.lastname: Bergeron
authors.forename: J
authors.initials: J
authors.lastname: Ostermann
mesh_terms: D000818:Animals; D000906:Antibodies / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D020126:Brefeldin A / Q000494:pharmacology*; D016466:CHO Cells; D002499:Centrifugation, Density Gradient; D020756:Coatomer Protein / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D006224:Cricetinae; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D005816:Genetic Complementation Test; D006031:Glycosylation; D006056:Golgi Apparatus / Q000737:chemistry / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D013696:Temperature; D013997:Time Factors; D014721:Vesicular stomatitis Indiana virus; D014759:Viral Envelope Proteins / Q000378:metabolism
chemical_list: D000906:Antibodies; D020756:Coatomer Protein; C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D014759:Viral Envelope Proteins; D020126:Brefeldin A