title: The aqueous pore through the translocon has a diameter of 40-60 A during cotranslational protein translocation at the ER membrane.
abstract: Eukaryotic secretory proteins are cotranslationally translocated through the endoplasmic reticulum (ER) membrane via aqueous pores that span the lipid bilayer. Fluorescent probes were incorporated into nascent secretory proteins using modified Lys-tRNAs, and the resulting nascent chains were sealed off from the cytosol in fully assembled translocation intermediates. Fluorescence quenching agents of different sizes were then introduced into the ER lumen in order to determine which were small enough to enter the pore and to quench the fluorescence of probes inside the ribosome and/or the pore. These accessibility studies showed that the aqueous pore in a functioning translocon is 40-60 A in diameter, making it the largest hole observed to date in a membrane that must maintain a permeability barrier.
authors.affiliation: Department of Medical Biochemistry and Genetics, Texas A&M University, College Station 77843-1114, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Hamman
authors.forename: J C
authors.initials: JC
authors.lastname: Chen
authors.forename: E E
authors.initials: EE
authors.lastname: Johnson
authors.forename: A E
authors.initials: AE
authors.lastname: Johnson
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan; D000818:Animals; D001693:Biological Transport, Active; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005456:Fluorescent Dyes; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009243:NAD / Q000378:metabolism; D010539:Permeability; D014176:Protein Biosynthesis; D011487:Protein Conformation; D012357:RNA, Transfer, Lys / Q000378:metabolism; D011817:Rabbits; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D005456:Fluorescent Dyes; D007140:Immunoglobulin Fab Fragments; D008051:Lipid Bilayers; D008565:Membrane Proteins; D012357:RNA, Transfer, Lys; D014867:Water; D009243:NAD; D009327:4-Chloro-7-nitrobenzofurazan