Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 396, Issue 1, Pages 221-229Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2009.11.036
Keywords
marginally hydrophobic helix; membrane protein; topology; hydrophobicity
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Funding
- Swedish Cancer Foundation
- Swedish Foundation for Strategic Research
- Swedish Research Council
- Stiftelserna Riksforbundet Cystisk Fibros Forskningsfond
- Anders Malmstens Minnesfond
- Magnus Bergvalls Stiftelse
- Henrik Granholms Stiftelse
- Carl Tryggers Stiftelse
- European Union [FP6-LSHG-CT-2003-503265, FP6-LSHG-CT-2004-512092, FP7-HEALTH-F4-2007-201924]
- Academy of Finland
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In mammalian cells, most integral membrane proteins are initially inserted into the endoplasmic reticulum membrane by the so-called Sec61 translocon. However, recent predictions suggest that many transmembrane helices (TMHs) in multispanning membrane proteins are not sufficiently hydrophobic to be recognized as such by the translocon. In this study, we have screened 16 marginally hydrophobic TMHs from membrane proteins of known three-dimensional structure. Indeed, most of these TMHs do not insert efficiently into the endoplasmic reticulum membrane by themselves. To test if loops or TMHs immediately upstream or downstream of a marginally hydrophobic helix might influence the insertion efficiency, insertion of marginally hydrophobic helices was also studied in the presence of their neighboring loops and helices. The results show that flanking loops and nearest-neighbor TMHs are sufficient to ensure the insertion of many marginally hydrophobic helices. However, for at least two of the marginally hydrophobic helices, the local interactions are not enough, indicating that post-insertional rearrangements are involved in the folding of these proteins. (C) 2009 Elsevier Ltd. All rights reserved.
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