title: Structural interactions between lipids, water and S1-S4 voltage-sensing domains.
abstract: Membrane proteins serve crucial signaling and transport functions, yet relatively little is known about their structures in membrane environments or how lipids interact with these proteins. For voltage-activated ion channels, X-ray structures suggest that the mobile voltage-sensing S4 helix would be exposed to the membrane, and functional studies reveal that lipid modification can profoundly alter channel activity. Here, we use solid-state NMR to investigate structural interactions of lipids and water with S1-S4 voltage-sensing domains and to explore whether lipids influence the structure of the protein. Our results demonstrate that S1-S4 domains exhibit extensive interactions with lipids and that these domains are heavily hydrated when embedded in a membrane. We also find evidence for preferential interactions of anionic lipids with S1-S4 domains and that these interactions have lifetimes on the timescale of ≤ 10(-3)s. Arg residues within S1-S4 domains are well hydrated and are positioned in close proximity to lipids, exhibiting local interactions with both lipid headgroups and acyl chains. Comparative studies with a positively charged lipid lacking a phosphodiester group reveal that this lipid modification has only modest effects on the structure and hydration of S1-S4 domains. Taken together, our results demonstrate that Arg residues in S1-S4 voltage-sensing domains reside in close proximity to the hydrophobic interior of the membrane yet are well hydrated, a requirement for carrying charge and driving protein motions in response to changes in membrane voltage.
authors.affiliation: Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. klausg@mail.nih.gov
authors.forename: Dmitriy
authors.initials: D
authors.lastname: Krepkiy
authors.forename: Klaus
authors.initials: K
authors.lastname: Gawrisch
authors.forename: Kenton J
authors.initials: KJ
authors.lastname: Swartz
mesh_terms: D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000502:physiology; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D008564:Membrane Potentials / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D017434:Protein Structure, Tertiary; D014867:Water / Q000737:chemistry*
chemical_list: D007473:Ion Channels; D008051:Lipid Bilayers; D008055:Lipids; D008565:Membrane Proteins; D014867:Water