title: Novel cargo-binding site in the beta and delta subunits of coatomer.
abstract: Arginine (R)-based ER localization signals are sorting motifs that confer transient ER localization to unassembled subunits of multimeric membrane proteins. The COPI vesicle coat binds R-based signals but the molecular details remain unknown. Here, we use reporter membrane proteins based on the proteolipid Pmp2 fused to GFP and allele swapping of COPI subunits to map the recognition site for R-based signals. We show that two highly conserved stretches--in the beta- and delta-COPI subunits--are required to maintain Pmp2GFP reporters exposing R-based signals in the ER. Combining a deletion of 21 residues in delta-COP together with the mutation of three residues in beta-COP gave rise to a COPI coat that had lost its ability to recognize R-based signals, whilst the recognition of C-terminal di-lysine signals remained unimpaired. A homology model of the COPI trunk domain illustrates the recognition of R-based signals by COPI.
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg, Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Michelsen
authors.forename: Volker
authors.initials: V
authors.lastname: Schmid
authors.forename: Jutta
authors.initials: J
authors.lastname: Metz
authors.forename: Katja
authors.initials: K
authors.lastname: Heusser
authors.forename: Urban
authors.initials: U
authors.lastname: Liebel
authors.forename: Torsten
authors.initials: T
authors.lastname: Schwede
authors.forename: Anne
authors.initials: A
authors.lastname: Spang
authors.forename: Blanche
authors.initials: B
authors.lastname: Schwappach
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000378:metabolism; D000595:Amino Acid Sequence; D001120:Arginine; D001665:Binding Sites; D020756:Coatomer Protein / Q000737:chemistry* / Q000378:metabolism*; D017124:Conserved Sequence; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D021382:Protein Sorting Signals; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism*; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D040681:Structural Homology, Protein
chemical_list: D033961:Adaptor Protein Complex 1; D020756:Coatomer Protein; D050505:Mutant Proteins; D021382:Protein Sorting Signals; D021122:Protein Subunits; D001120:Arginine