title: Competition between neighboring topogenic signals during membrane protein insertion into the ER.
abstract: To better define the mechanism of membrane protein insertion into the membrane of the endoplasmic reticulum, we measured the kinetics of translocation across microsomal membranes of the N-terminal lumenal tail and the lumenal domain following the second transmembrane segment (TM2) in the multispanning mouse protein Cig30. In the wild-type protein, the N-terminal tail translocates across the membrane before the downstream lumenal domain. Addition of positively charged residues to the N-terminal tail dramatically slows down its translocation and allows the downstream lumenal domain to translocate at the same time as or even before the N-tail. When TM2 is deleted, or when the loop between TM1 and TM2 is lengthened, addition of positively charged residues to the N-terminal tail causes TM1 to adopt an orientation with its N-terminal end in the cytoplasm. We suggest that the topology of the TM1-TM2 region of Cig30 depends on a competition between TM1 and TM2 such that the transmembrane segment that inserts first into the ER membrane determines the final topology.
authors.affiliation: Department of Biochemistry and Biophysics, Stockholm University, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Monné
authors.forename: Tara
authors.initials: T
authors.lastname: Hessa
authors.forename: Laura
authors.initials: L
authors.lastname: Thissen
authors.forename: Gunnar
authors.initials: G
authors.lastname: von Heijne
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D021381:Protein Transport; D015398:Signal Transduction
chemical_list: D008565:Membrane Proteins