title: TRAP assists membrane protein topogenesis at the mammalian ER membrane.
abstract: Membrane protein insertion and topogenesis generally occur at the Sec61 translocon in the endoplasmic reticulum membrane. During this process, membrane spanning segments may adopt two distinct orientations with either their N- or C-terminus translocated into the ER lumen. While different topogenic determinants in membrane proteins, such as flanking charges, polypeptide folding, and hydrophobicity, have been identified, it is not well understood how the translocon and/or associated components decode them. Here we present evidence that the translocon-associated protein (TRAP) complex is involved in membrane protein topogenesis in vivo. Small interfering RNA (siRNA)-mediated silencing of the TRAP complex in HeLa cells enhanced the topology effect of mutating the flanking charges of a signal-anchor, but not of increasing signal hydrophobicity. The results suggest a role of the TRAP complex in moderating the 'positive-inside' rule.
authors.affiliation: CSCM, Institute of Biology, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany. Electronic address: sommer@bio.uni-luebeck.de.
authors.forename: Nicole
authors.initials: N
authors.lastname: Sommer
authors.affiliation: Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
authors.forename: Tina
authors.initials: T
authors.lastname: Junne
authors.affiliation: CSCM, Institute of Biology, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany.
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Kalies
authors.affiliation: Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Spiess
authors.affiliation: CSCM, Institute of Biology, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany.
authors.forename: Enno
authors.initials: E
authors.lastname: Hartmann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007425:Intracellular Membranes / Q000378:metabolism*; D008322:Mammals / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D050505:Mutant Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; C066973:signal sequence receptor
keywords: Endoplasmic reticulum; Membrane protein topogenesis; RNA interference; Sec61 complex; Translocon associated proteins