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Dislocation by the m-AAA protease increases the threshold hydrophobicity for retention of transmembrane helices in the inner membrane of yeast mitochondria
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Science for Life Laboratory (SciLifeLab).
2012 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Sorting of mitochondrial inner membraneproteins is a complex process where transloconsand proteases function in a concerted way.Many inner membrane proteins insert into themembrane via the TIM23 translocon and someare then further acted upon by themitochondrial m-AAA protease, a molecularmotor capable of dislocating proteins from theinner membrane. This raises the possibility thatthe threshold hydrophobicity for the retentionof transmembrane segments in the innermembrane is different, depending on whetherthey belong to membrane proteins that are m-AAA protease substrate or not. Here, usingmodel transmembrane segments engineeredinto m-AAA protease-dependent proteins, weshow that the threshold hydrophobicity formembrane retention measured in yeast cells inthe absence of a functional m-AAA protease ismarkedly lower than that measured in itspresence. Whether a given hydrophobicsegment in a mitochondrial inner membraneprotein will ultimately form a transmembranehelix may therefore depend on whether or not,during biogenesis, it will be exposed to thepulling force exerted by the m-AAA protease.

Place, publisher, year, edition, pages
National Category
Natural Sciences
URN: urn:nbn:se:su:diva-83481OAI: diva2:575961
Available from: 2012-12-11 Created: 2012-12-11 Last updated: 2012-12-12Bibliographically approved
In thesis
1. Translocation of proteins into and across the bacterial and mitochondrial inner membranes
Open this publication in new window or tab >>Translocation of proteins into and across the bacterial and mitochondrial inner membranes
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]


Translocons are dynamic protein complexes with the ability to respond to specific signals and to transport polypeptides between two distinct environments. The Sec-type translocons are examples of such machineries that can interconvert between a pore forming conformation that translocates proteins across the membrane, and a channel-like conformation that integrates proteins into the membrane by lateral opening.

This thesis aims to identify the signals encoded in the amino acid sequence of the translocating polypeptides that trigger the translocon to release defined segments into the membrane. The selected systems are the SecYEG translocon and the TIM23 complex responsible for inserting proteins into the bacterial and the mitochondrial inner membrane, respectively.

These two translocons have been challenged in vivo with designed polypeptide segments and their insertion efficiency into the membrane was measured. This allowed identification of the sequence requirements that govern SecYEG- and TIM23-mediated membrane integration. For these two systems, “biological” hydrophobicity scales have been determined, giving the contributions of each of the 20 amino acids to the overall free energy of insertion of a transmembrane segment into the membrane.

A closer analysis of the mitochondrial system has made it possible to additionally investigate the process of membrane dislocation mediated by the m-AAA protease. The threshold hydrophobicity required for a transmembrane segment to remain in the mitochondrial inner membrane after TIM23-mediated integration depends on whether the segment will be further acted upon by the m-AAA protease.

Finally, an experimental approach is presented to distinguish between different protein sorting pathways at the level of the TIM23 complex, i.e., conservative sorting vs. stop-transfer pathways. The results suggest a connection between the metabolic state of the cell and the import of proteins into the mitochondria.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2012. 86 p.
Escherichia coli, mitochondria, Saccharomyces cerevisiae, SecYEG, TIM23, transmembrane helix
National Category
Biochemistry and Molecular Biology
Research subject
urn:nbn:se:su:diva-83234 (URN)978-91-7447-600-2 (ISBN)
Public defence
2013-01-11, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)

At the time of doctoral defence the following papers were unpublished and had a status as follows: Paper nr. 1: Manuscript; Paper nr. 4: Manuscript

Available from: 2012-12-20 Created: 2012-12-06 Last updated: 2012-12-21Bibliographically approved

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Calado Botelho, Salomé
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