Transitions between conformational substates of membrane proteins can be driven by torsional librations in theprotein that may be coupled to librational fluctuations of the lipid chains. Here, librational motion of spin-labeled lipid chains inmembranous Na,K-ATPase is investigated by spin-echo electron paramagnetic resonance. Lipids at the protein interface aretargeted 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 thebilayer regions of the membrane by using spectra from dispersions of the extracted membrane lipids. Lipid librations at the proteininterface have a flat profile with chain position, whereas librational fluctuations of the bilayer lipids increase pronouncedlyfrom C-9 onward, then flatten off toward the terminal methyl end of the chains. This difference is accounted for by increasedtorsional amplitude at the chain ends in bilayers, while the amplitude remains restricted throughout the chain at the protein interfacewith a limited lengthening in correlation time. The temperature dependence of chain librations at the protein interfacestrongly resembles that of the spin-labeled protein side chains, suggesting solvent-mediated transitions in the protein are drivenby fluctuations in the lipid environment.
Lipid Librations at the Interface with the Na,K-ATPase
GUZZI, Rita;BARTUCCI, Rosa;
2015-01-01
Abstract
Transitions between conformational substates of membrane proteins can be driven by torsional librations in theprotein that may be coupled to librational fluctuations of the lipid chains. Here, librational motion of spin-labeled lipid chains inmembranous Na,K-ATPase is investigated by spin-echo electron paramagnetic resonance. Lipids at the protein interface aretargeted 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 thebilayer regions of the membrane by using spectra from dispersions of the extracted membrane lipids. Lipid librations at the proteininterface have a flat profile with chain position, whereas librational fluctuations of the bilayer lipids increase pronouncedlyfrom C-9 onward, then flatten off toward the terminal methyl end of the chains. This difference is accounted for by increasedtorsional amplitude at the chain ends in bilayers, while the amplitude remains restricted throughout the chain at the protein interfacewith a limited lengthening in correlation time. The temperature dependence of chain librations at the protein interfacestrongly resembles that of the spin-labeled protein side chains, suggesting solvent-mediated transitions in the protein are drivenby fluctuations in the lipid environment.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.