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The Sec62/63 translocon facilitates membrane insertion and C-terminal translocation of multi-spanning membrane proteins
Seoul National University, Seoul, South Korea.
Seoul National University.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Seoul National University, Seoul, South Korea.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Majority of membrane proteins are co-translationally translocated. The Sec62/Sec63 complex which mediates post-translational translocation of a subset of primarily secretory proteins into the endoplasmic reticulum (ER),  therefore has been thought uninvolved in targeting and translocation of membrane proteins. By systematic analysis of single and multi-spanning membrane proteins with broad sequence context; varying hydrophobicity, flanking charged residues and orientation of transmembrane (TM) segments, in a set of Sec62 mutant yeast strains, we show that mutations in the N-terminal cytosolic domain of Sec62 impair interaction with Sec63 and lead to defects in membrane insertion and the C-terminal translocation of membrane proteins. These results reveal an unappreciated function of the Sec62/Sec63 translocon as a general membrane chaperone that regulates topogenesis of membrane proteins in the eukaryotic cell.

Keyword [en]
endoplasmic reticulum, co-translational translocation, Sec61, topology, yeast
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:su:diva-95674OAI: oai:DiVA.org:su-95674DiVA: diva2:661246
Available from: 2013-11-01 Created: 2013-11-01 Last updated: 2013-11-05
In thesis
1. Membrane Protein Biogenesis in Saccharomyces cerevisiae
Open this publication in new window or tab >>Membrane Protein Biogenesis in Saccharomyces cerevisiae
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Membranes are hydrophobic barriers that define the outer boundaries and internal compartments of living cells. Membrane proteins are the gates in these barriers, and they perform vital functions in the highly regulated transport of matter and information across membranes. Membrane proteins destined for the endoplasmic reticulum are targeted either co- or post-translationally to the Sec61 translocon, the major translocation machinery in eukaryotic cells, which allows for lateral partitioning of hydrophobic segments into the lipid bilayer. This thesis aims to acquire insights into the mechanism of membrane protein insertion and the role of different translocon components in targeting, insertion and topogenesis, using the yeast Saccharomyces cerevisiae as a model organism.

By measuring the insertion efficiency of a set of model proteins, we studied the sequence requirements for Sec61-mediated insertion of an α-helical transmembrane segment and established a ‘biological hydrophobicity scale’ in yeast, which describes the individual contributions of the 20 amino acids to insertion. Systematic mutagenesis and photo-crosslinking of the Sec61 translocon revealed key residues in the lateral gate that modulate the threshold hydrophobicity for membrane insertion and transmembrane segment orientation. Further, my studies demonstrate that the translocon-associated Sec62 is important not only for post-translational targeting, but also for the insertion and topogenesis of moderately hydrophobic signal anchor proteins and the C-terminal translocation of multi-spanning membrane proteins. Finally, nuclearly encoded mitochondrial membrane proteins were found to evade mis-targeting to the endoplasmic reticulum by containing short C-terminal tails.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2013. 72 p.
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-95376 (URN)978-91-7447-798-6 (ISBN)
Public defence
2013-12-13, Nordenskiöld Lecture Hall, Geo-Science Building, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 4: Manuscript; Paper 5: Manuscript

Available from: 2013-11-21 Created: 2013-10-26 Last updated: 2014-07-25Bibliographically approved

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