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Folding of Aquaporin 1: Multiple evidence that helix 3 can shift out of the membrane core

Minttu T. Virkki, Nitin Agrawal, Elin Edsbäcker, Susana Cristobal, View ORCID ProfileArne Elofsson, View ORCID ProfileAnni Kauko
doi: https://doi.org/10.1101/014167
Minttu T. Virkki
*Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University SE-171 21 Solna, Sweden E-mail:
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  • For correspondence: minttu.virkki@scilifelab.se
Nitin Agrawal
†Department of Biosciences, Biochemistry, Åbo Akademi, FI-20520 Turku, Finland E-mail:
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  • For correspondence: nagrawal@abo.fi
Elin Edsbäcker
‡Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University SE-171 21 Solna, Sweden E-mail:
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  • For correspondence: elin.edsbacker@stud.ki.se
Susana Cristobal
§Department of Clinical and Experimental Medicine, Cell Biology, Faculty of Health Science, Linköping University, Linköping, Sweden and Departments of Physiology, IKERBASQUE, Basque Foundation for Science, Faculty of Medicine and Dentistry, University of the Basque Country, Leioa, Spain E-mail:
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  • For correspondence: susana.cristobal@liu.se
Arne Elofsson
¶Department of Biochemistry and Biophysics and Science for Life Laboratory, Stockholm University SE-171 21 Solna, Sweden E-mail:
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Anni Kauko
∥Department of Biosciences, Biochemistry, Åbo Akademi, FI-20520 Turku, Finland E-mail:
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  • ORCID record for Anni Kauko
  • For correspondence: anni.kauko@iki.fi
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Abstract

The folding of most integral membrane proteins follows a two-step process: Initially, individual transmembrane helices are inserted into the membrane by the Sec translocon. Thereafter, these helices fold to shape the final conformation of the protein. However, for some proteins, including Aquaporin 1 (AQP1), the folding appears to follow a more complicated path. AQP1 has been reported to first insert as a four-helical intermediate, where helix 2 and 4 are not inserted into the membrane. In a second step this intermediate is folded into a six-helical topology. During this process, the orientation of the third helix is inverted. Here, we propose a mechanism for how this reorientation could be initiated: First, helix 3 slides out from the membrane core resulting in that the preceding loop enters the membrane. The final conformation could then be formed as helix 2, 3 and 4 are inserted into the membrane and the reentrant regions come together. We find support for the first step in this process by showing that the loop preceding helix 3 can insert into the membrane. Further, hydrophobicity curves, experimentally measured insertion efficiencies and MD-simulations suggest that the barrier between these two hydrophobic regions is relatively low, supporting the idea that helix 3 can slide out of the membrane core, initiating the rearrangement process

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Posted January 23, 2015.
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Folding of Aquaporin 1: Multiple evidence that helix 3 can shift out of the membrane core
Minttu T. Virkki, Nitin Agrawal, Elin Edsbäcker, Susana Cristobal, Arne Elofsson, Anni Kauko
bioRxiv 014167; doi: https://doi.org/10.1101/014167
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Folding of Aquaporin 1: Multiple evidence that helix 3 can shift out of the membrane core
Minttu T. Virkki, Nitin Agrawal, Elin Edsbäcker, Susana Cristobal, Arne Elofsson, Anni Kauko
bioRxiv 014167; doi: https://doi.org/10.1101/014167

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