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Orientational Preferences of Neighboring Helices Can Drive ER Insertion of a Marginally Hydrophobic Transmembrane Helix
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Science for Life Laboratory (SciLifeLab).
2012 (English)In: Molecular Cell, ISSN 1097-2765, E-ISSN 1097-4164, Vol. 45, no 4, 529-540 p.Article in journal (Refereed) Published
Abstract [en]

alpha-helical integral membrane proteins critically depend on the correct insertion of their transmembrane alpha helices into the lipid bilayer for proper folding, yet a surprisingly large fraction of the transmembrane alpha helices in multispanning integral membrane proteins are not sufficiently hydrophobic to insert into the target membrane by themselves. How can such marginally hydrophobic segments nevertheless form transmembrane helices in the folded structure? Here, we show that a transmembrane helix with a strong orientational preference (N-cyt-C-lum or N-lum-C-cyt) can both increase and decrease the hydrophobicity threshold for membrane insertion of a neighboring, marginally hydrophobic helix. This effect helps explain the missing hydrophobicity in polytopic membrane proteins.

Place, publisher, year, edition, pages
2012. Vol. 45, no 4, 529-540 p.
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:su:diva-76981DOI: 10.1016/j.molcel.2011.12.024ISI: 000300753800012OAI: oai:DiVA.org:su-76981DiVA: diva2:531099
Note

4

Available from: 2012-06-05 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Membrane protein topogenesis
Open this publication in new window or tab >>Membrane protein topogenesis
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The membranes of cells are highly complex and heterogeneous structures that fulfill multiple vital tasks. They form thin barriers that seal out the environment, thus defining the cell’s boundaries. They mediate the selective exchange of information and substances between the inside and outside of cells, thus making cellular life and survival possible and allowing fast adaptation to changing conditions. Not least importantly, they harbor key components of many essential processes such as the photosynthesis and respiration. Membranes are composed of a largely apolar lipid matrix densely punctuated with a large number of different proteins. These so-called membrane proteins usually span the lipid matrix and protrude out into the space on either side of the membrane.

Over millions of years of evolution, cells have developed an incredible machinery to facilitate the insertion of membrane proteins into the membrane. Our understanding of these machines and the insertion processes they mediate has reached a point where we have a very good picture of membrane protein biogenesis in various types of cells. However, more data still needs to be collected to completely comprehend the complex molecular mechanisms and the physical chemistry that underlies the different insertion processes.

The work presented in this thesis contributes to that understanding. More precisely, we have studied how weakly hydrophobic transmembrane elements of membrane proteins, which cannot spontaneously enter the largely apolar membrane matrices, are efficiently incorporated. Indeed, such elements are quite common in membrane proteins and our work has lead to the formulation of a novel mechanism for how they can be integrated into biological membranes.

We have also added to the understanding of the physical chemistry that underlies the membrane insertion process by systematically introducing non-proteinogenic amino acids into a membrane-spanning segment of a membrane protein and studying its membrane insertion capability.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2015. 69 p.
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-113384 (URN)978-91-7649-089-1 (ISBN)
Public defence
2015-03-09, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2015-02-15 Created: 2015-01-29 Last updated: 2015-03-11Bibliographically approved

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