title: Water penetration profile at the protein-lipid interface in Na,K-ATPase membranes.
abstract: The affinity of ionized fatty acids for the Na,K-ATPase is used to determine the transmembrane profile of water penetration at the protein-lipid interface. The standardized intensity of the electron spin echo envelope modulation (ESEEM) from (2)H-hyperfine interaction with D2O is determined for stearic acid, n-SASL, spin-labeled systematically at the C-n atoms throughout the chain. In both native Na,K-ATPase membranes from shark salt gland and bilayers of the extracted membrane lipids, the D2O-ESEEM intensities of fully charged n-SASL decrease progressively with position down the fatty acid chain toward the terminal methyl group. Whereas the D2O intensities decrease sharply at the n = 9 position in the lipid bilayers, a much broader transition region in the range n = 6 to 10 is found with Na,K-ATPase membranes. Correction for the bilayer population in the membranes yields the intrinsic D2O-intensity profile at the protein-lipid interface. For positions at either end of the chains, the D2O concentrations at the protein interface are greater than in the lipid bilayer, and the positional profile is much broader. This reveals the higher polarity, and consequently higher intramembrane water concentration, at the protein-lipid interface. In particular, there is a significant water concentration adjacent to the protein at the membrane midplane, unlike the situation in the bilayer regions of this cholesterol-rich membrane. Experiments with protonated fatty acid and phosphatidylcholine spin labels, both of which have a considerably lower affinity for the Na,K-ATPase, confirm these results.
authors.affiliation: Department of Physics, Molecular Biophysics Laboratory and CNISM Unit, University of Calabria, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy.
authors.forename: Rosa
authors.initials: R
authors.lastname: Bartucci
authors.affiliation: Department of Physics, Molecular Biophysics Laboratory and CNISM Unit, University of Calabria, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy.
authors.forename: Rita
authors.initials: R
authors.lastname: Guzzi
authors.affiliation: Department of Biomedicine, Aarhus University, 8000 Aarhus, Denmark.
authors.forename: Mikael
authors.initials: M
authors.lastname: Esmann
authors.affiliation: Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany. Electronic address: dmarsh@gwdg.de.
authors.forename: Derek
authors.initials: D
authors.lastname: Marsh
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002463:Cell Membrane Permeability; D005227:Fatty Acids / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism*; D008958:Models, Molecular; D010713:Phosphatidylcholines / Q000378:metabolism; D011487:Protein Conformation; D011522:Protons; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism*; D013113:Spin Labels; D014867:Water / Q000378:metabolism*
chemical_list: D005227:Fatty Acids; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D011522:Protons; D013113:Spin Labels; D014867:Water; D000254:Sodium-Potassium-Exchanging ATPase