title: Autonomous transmembrane segment S4 of the voltage sensor domain partitions into the lipid membrane.
abstract: The S4 transmembrane segment in voltage-gated ion channels, a highly basic alpha helix, responds to changes in membrane potential and induces channel opening. Earlier work by others indicates that the S4 segment interacts with lipids in plasma membrane, but its mechanism is unclear. Working with synthetic tryptophan-labeled S4 peptides, we characterized binding of autonomous S4 to lipid membranes. The binding free energy (5.2 +/- 0.2 kcal/mol) of the peptide-lipid interaction was estimated from the apparent dissociation constants, determined from the changes in anisotropy of tryptophan fluorescence induced by addition of lipid vesicles with 30 mol% phosphatidylglycerol. The results are in good agreement with the prediction based on the Wimley-White hydrophobicity scale for interfacial (IF) binding of an alpha-helical peptide to the lipid bilayer (6.98 kcal/mol). High salt inhibited the interaction, thus indicating that the peptide/membrane interaction has both electrostatic and non-electrostatic components. Furthermore, the synthetic S4 corresponding to the Shaker potassium channel was found to spontaneously penetrate into the negatively charged lipid membrane to a depth of about 9 A. Our results revealed important biophysical parameters that influence the interaction of S4 with the membrane: they include fluidity, surface charge, and surface pressure of the membrane, and the at helicity and regular spacing of basic amino-acid residues in the S4 sequence.
authors.affiliation: Department of Neuroscience and High Throughput Biology Center, Johns Hopkins University School of Medicine, 733 North Broadway, Baltimore, MD 21205, USA.
authors.forename: Venkataswarup
authors.initials: V
authors.lastname: Tiriveedhi
authors.forename: Melissa
authors.initials: M
authors.lastname: Miller
authors.forename: Peter
authors.initials: P
authors.lastname: Butko
authors.forename: Min
authors.initials: M
authors.lastname: Li
mesh_terms: D000595:Amino Acid Sequence; D016880:Anisotropy; D015640:Ion Channel Gating; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D055672:Static Electricity; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism; D053835:Unilamellar Liposomes / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D008563:Membrane Lipids; D010455:Peptides; D024642:Potassium Channels, Voltage-Gated; D053835:Unilamellar Liposomes; D014364:Tryptophan