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Sticky water surfaces: Helix-coil transitions suppressed in a cell-penetrating peptide at the air-water interface

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  • Denise K Schach, Max Planck Institute for Polymer Research
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  • Christoph Globisch, University of Konstanz
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  • Steven J Roeters, University of Amsterdam
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  • Sander Woutersen, University of Amsterdam
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  • Adrian Fuchs, Max Planck Institute for Polymer Research
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  • Clemens K Weiss, Max Planck Institute for Polymer Research
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  • Ellen H G Backus, Max Planck Institute for Polymer Research
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  • Katharina Landfester, Max Planck Institute for Polymer Research
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  • Mischa Bonn, Max Planck Institute for Polymer Research
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  • Christine Peter, University of Konstanz
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  • Tobias Weidner

GALA is a 30 amino acid synthetic peptide consisting of a Glu-Ala-Leu-Ala repeat and is known to undergo a reversible structural transition from a disordered to an α-helical structure when changing the pH from basic to acidic values. In its helical state GALA can insert into and disintegrate lipid membranes. This effect has generated much interest in GALA as a candidate for pH triggered, targeted drug delivery. GALA also serves as a well-defined model system to understand cell penetration mechanisms and protein folding triggered by external stimuli. Structural transitions of GALA in solution have been studied extensively. However, cell penetration is an interfacial effect and potential biomedical applications of GALA would involve a variety of surfaces, e.g., nanoparticles, lipid membranes, tubing, and liquid-gas interfaces. Despite the apparent importance of interfaces in the functioning of GALA, the effect of surfaces on the reversible folding of GALA has not yet been studied. Here, we use sum frequency generation vibrational spectroscopy (SFG) to probe the structural response of GALA at the air-water interface and IR spectroscopy to follow GALA folding in bulk solution. We combine the SFG data with molecular dynamics simulations to obtain a molecular-level picture of the interaction of GALA with the air-water interface. Surprisingly, while the fully reversible structural transition was observed in solution, at the water-air interface, a large fraction of the GALA population remained helical at high pH. This "stickiness" of the air-water interface can be explained by the stabilizing interactions of hydrophobic leucine and alanine side chains with the water surface.

Original languageEnglish
JournalJournal of Chemical Physics
Pages (from-to)22D517, 1-9
Number of pages9
Publication statusPublished - 2014
Externally publishedYes

    Research areas

  • Air, Amino Acid Sequence, Cell-Penetrating Peptides, Hydrogen-Ion Concentration, Hydrophobic and Hydrophilic Interactions, Molecular Dynamics Simulation, Peptides, Protein Structure, Secondary, Surface Properties, Water, Journal Article, Research Support, Non-U.S. Gov't

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