title: The carboxyl-terminal valine is required for transport of glycoprotein CD8 alpha from the endoplasmic reticulum to the intermediate compartment.
abstract: There is evidence that a carboxyl-terminal valine residue is an anterograde transport signal for type I transmembrane proteins. Removal of the signal would either delay glycosylation in the Golgi complex of proteins destined to recycle to the endoplasmic reticulum or determine accumulation in the endoplasmic reticulum of newly synthesized proteins destined for the plasma membrane. We used the human CD8 alpha glycoprotein to investigate the role of the carboxyl-terminal valine in the exocytic pathway. Using immunofluorescence light microscopy, metabolic labeling, and cell fractionation, we demonstrate that removal of the carboxyl-terminal valine residue delays transport of CD8 alpha from the endoplasmic reticulum to the intermediate compartment. Removal of the residue did not affect the other steps of the exocytic pathway or the folding/dimerization and glycosylation processes. Therefore, it is likely that this signal plays a role in the transport of CD8 alpha from the endoplasmic reticulum to the intermediate compartment either before or during the formation of the transport vesicles that drive the exit the protein from the endoplasmic reticulum.
authors.affiliation: Department of Biochemistry and Medical Biotechnology, University of Naples Federico II, 80131 Naples, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Iodice
authors.forename: S
authors.initials: S
authors.lastname: Sarnataro
authors.forename: S
authors.initials: S
authors.lastname: Bonatti
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D016827:CD8 Antigens / Q000737:chemistry* / Q000378:metabolism*; D002415:Cats; D002417:Cattle; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002645:Chickens; D003600:Cytosol / Q000378:metabolism; D019281:Dimerization; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005089:Exocytosis; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D008322:Mammals; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011148:Pongo pygmaeus; D021381:Protein Transport; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014633:Valine
chemical_list: D016827:CD8 Antigens; C431698:CD8alpha antigen; D011994:Recombinant Proteins; D014633:Valine