Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 425, Issue 4, Pages 830-840Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2012.12.001
Keywords
electrostatic interactions; helical hairpin; membrane integration; salt bridge; translocon
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Funding
- Spanish Ministry of Science and Innovation (MICINN, European Regional Development Fund) [BFU2009-08401, BIO2011-29792]
- EU
- Generalitat Valenciana [ACOMP/2012/226]
- Basque Government [GIU06/42]
- Swedish National Research Center
- EU FP7 through the EDICT grant [FP7-HEALTH-F4-2007-201924]
- Formacion de Profesorado Universitario fellowship from the Spanish Ministry of Education
- Swedish e-Science Research Center
- Vinnova
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alpha-Helical hairpins, consisting of a pair of closely spaced transmembrane (TM) helices that are connected by a short interfacial turn, are the simplest structural motifs found in multi-spanning membrane proteins. In naturally occurring hairpins, the presence of polar residues is common and predicted to complicate membrane insertion. We postulate that the pre-packing process offsets any energetic cost of allocating polar and charged residues within the hydrophobic environment of biological membranes. Consistent with this idea, we provide here experimental evidence demonstrating that helical hairpin insertion into biological membranes can be driven by electrostatic interactions between closely separated, poorly hydrophobic sequences. Additionally, we observe that the integral hairpin can be stabilized by a short loop heavily populated by turn-promoting residues. We conclude that the combined effect of TM-TM electrostatic interactions and tight turns plays an important role in generating the functional architecture of membrane proteins and propose that helical hairpin motifs can be acquired within the context of the Sec61 translocon at the early stages of membrane protein biosynthesis. Taken together, these data further underline the potential complexities involved in accurately predicting TM domains from primary structures. (c) 2012 Elsevier Ltd. All rights reserved.
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