title: Orientation of internal signal-anchor sequences at the Sec61 translocon.
abstract: Translocation and insertion of secretory and membrane proteins at the endoplasmic reticulum are mediated by the Sec61 translocon. Evidence from in vivo as well as in vitro experiments indicates that N-terminal signal-anchor sequences initially insert N-first before they invert their orientation to translocate the C-terminus. Inversion is driven by flanking charges according to the positive-inside rule and inhibited by increased signal hydrophobicity. Here, we show that upon extending the N-terminal hydrophilic domain preceding the signal core to more than ~20 residues, the insertion behavior changes. Apparent signal inversion and the effect of hydrophobicity are largely lost, suggesting that N-first insertion is limited to N-terminal signal anchors. Extended N-domains sterically hinder N-translocation in a length-dependent manner also for reverse signal anchors with inverted flanking charges. The results indicate a mechanistic difference in the insertion process of N-terminal and internal signal sequences.
authors.affiliation: Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
authors.forename: Lucyna
authors.initials: L
authors.lastname: Kocik
authors.forename: Tina
authors.initials: T
authors.lastname: Junne
authors.forename: Martin
authors.initials: M
authors.lastname: Spiess
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D021382:Protein Sorting Signals; D021381:Protein Transport; D000069816:SEC Translocation Channels
chemical_list: D008565:Membrane Proteins; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels