title: A Conserved Di-Basic Motif of Drosophila Crumbs Contributes to Efficient ER Export.
abstract: The Drosophila type I transmembrane protein Crumbs is an apical determinant required for the maintenance of apico-basal epithelial cell polarity. The level of Crumbs at the plasma membrane is crucial, but how it is regulated is poorly understood. In a genetic screen for regulators of Crumbs protein trafficking we identified Sar1, the core component of the coat protein complex II transport vesicles. sar1 mutant embryos show a reduced plasma membrane localization of Crumbs, a defect similar to that observed in haunted and ghost mutant embryos, which lack Sec23 and Sec24CD, respectively. By pulse-chase assays in Drosophila Schneider cells and analysis of protein transport kinetics based on Endoglycosidase H resistance we identified an RNKR motif in Crumbs, which contributes to efficient ER export. The motif identified fits the highly conserved di-basic RxKR motif and mediates interaction with Sar1. The RNKR motif is also required for plasma membrane delivery of transgene-encoded Crumbs in epithelial cells of Drosophila embryos. Our data are the first to show that a di-basic motif acts as a signal for ER exit of a type I plasma membrane protein in a metazoan organism.
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr.108, 01307, Dresden, Germany.|Present address: Membrane Traffic and Cell Division, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris, France.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kumichel
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr.108, 01307, Dresden, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Kapp
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr.108, 01307, Dresden, Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Knust
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; C064360:crb protein, Drosophila; C533273:Sar1 protein, Drosophila; D020559:Monomeric GTP-Binding Proteins
keywords: COPII; Crumbs; Drosophila; ER export; Sar1; di-basic motif