title: Lipid Librations at the Interface with the Na,K-ATPase.
abstract: Transitions between conformational substates of membrane proteins can be driven by torsional librations in the protein that may be coupled to librational fluctuations of the lipid chains. Here, librational motion of spin-labeled lipid chains in membranous Na,K-ATPase is investigated by spin-echo electron paramagnetic resonance. Lipids at the protein interface are targeted by using negatively charged spin-labeled fatty acids that display selectivity of interaction with the Na,K-ATPase. Echo-detected electron paramagnetic resonance spectra from native membranes are corrected for the contribution from the bilayer regions of the membrane by using spectra from dispersions of the extracted membrane lipids. Lipid librations at the protein interface have a flat profile with chain position, whereas librational fluctuations of the bilayer lipids increase pronouncedly from C-9 onward, then flatten off toward the terminal methyl end of the chains. This difference is accounted for by increased torsional amplitude at the chain ends in bilayers, while the amplitude remains restricted throughout the chain at the protein interface with a limited lengthening in correlation time. The temperature dependence of chain librations at the protein interface strongly resembles that of the spin-labeled protein side chains, suggesting solvent-mediated transitions in the protein are driven by fluctuations in the lipid environment.
authors.affiliation: Department of Physics, Molecular Biophysics Laboratory and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Material Unit, University of Calabria, Ponte P. Bucci, Rende, Italy.
authors.forename: Rita
authors.initials: R
authors.lastname: Guzzi
authors.affiliation: Department of Physics, Molecular Biophysics Laboratory and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Material Unit, University of Calabria, Ponte P. Bucci, Rende, Italy.
authors.forename: Rosa
authors.initials: R
authors.lastname: Bartucci
authors.affiliation: Department of Biomedicine, Aarhus University, Aarhus, Denmark.
authors.forename: Mikael
authors.initials: M
authors.lastname: Esmann
authors.affiliation: Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany. Electronic address: dmarsh@gwdg.de.
authors.forename: Derek
authors.initials: D
authors.lastname: Marsh
mesh_terms: D005227:Fatty Acids / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry*; D054159:Torsion, Mechanical
chemical_list: D005227:Fatty Acids; D008051:Lipid Bilayers; D000254:Sodium-Potassium-Exchanging ATPase