title: Monotopic topology is required for lipid droplet targeting of ancient ubiquitous protein 1.
abstract: Ancient ubiquitous protein 1 (AUP1) is a multifunctional protein, which acts on both lipid droplets (LDs) and the endoplasmic reticulum (ER) membrane. Double localization to these two organelles, featuring very different membrane characteristics, was observed also for several other integral proteins, but little is known about the signals and mechanisms behind dual protein targeting to ER and LDs. Here we dissect the AUP1 targeting signals by analyses of localization and topology of several deletion and point mutants. We found that AUP1 is inserted into the membrane of the ER in a monotopic hairpin fashion, and subsequently transported to the hemi-membrane of LDs. A single domain localized in the N-terminal part of AUP1 enables its ER residence, the monotopic insertion, and the LD localization. Different specific residues within this multifunctional domain are responsible for achieving the complex spatial distribution pattern. A mutation of three amino acids, which changes AUP1 topology from hairpin to transmembrane, abolishes LD localization. These findings suggest that the cell is able to target a protein to multiple intracellular locations using a single domain.
authors.affiliation: LIMES Life and Medical Sciences Institute, University of Bonn, D-53115 Bonn, Germany.
authors.forename: Ana
authors.initials: A
authors.lastname: Stevanovic
authors.forename: Christoph
authors.initials: C
authors.lastname: Thiele
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D050356:Lipid Metabolism; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D015388:Organelles / Q000378:metabolism*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport
chemical_list: C464942:AUP1 protein, human; D002352:Carrier Proteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals