This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.104.046631v1 87/6/3873    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Erilov, D. A. Articles by Sportelli, L. Search for Related Content PubMed PubMed Citation Articles by Erilov, D. A. Articles by Sportelli, L.

Librational Motion of Spin-Labeled Lipids in High-Cholesterol Containing Membranes from Echo-Detected EPR Spectra

Denis A. Erilov ^* , Rosa Bartucci ^*, Rita Guzzi ^*, Derek Marsh , Sergei A. Dzuba  and Luigi Sportelli ^*

^* Dipartimento di Fisica and Unità Instituto Nazionale per la Fisica della Materia, Università della Calabria, Arcavacata di Rende (CS), Italy; Department of Physics, Novosibirsk State University, Novosibirsk, Russian Federation; Max-Planck-Institut für Biophysikalische Chemie, Abteilung Spektroskopie, Göttingen, Germany; and Institute of Chemical Kinetics and Combustion, Russian Academy of Science, Novosibirsk, Russian Federation

Correspondence: Address reprint requests to Dr. R. Bartucci, Dipartimento di Fisica ed Unità INFM, Università della Calabria, I-87036 Arcavacata di Rende (CS), Italia. E-mail: bartucci{at}fis.unical.it.

Two-pulse, echo-detected (ED) electron paramagnetic resonance (EPR) spectroscopy was used to study the librational motions of spin-labeled lipids in membranes of dipalmitoylphosphatidylcholine + 50 mol % cholesterol. The temperature dependence, over the range 77–240 K, and the dependence on position of spin-labeling in the sn-2 chain (n = 5, 7, 10, 12, and 14) of the phospholipid, were characterized in detail. The experimental ED-spectra were corrected for instantaneous spin diffusion arising from static spin-spin interactions, by using spectra recorded at 77 K, where motional contributions are negligible. Simulations according to a model of rapid, small-amplitude librations about an axis whose direction is randomly distributed are able to describe the experimental spectra. Calibrations, in terms of the amplitude-correlation time product, ²_c, were constructed for diagnostic spectral line-height ratios at different echo delay times, and for relaxation spectra obtained from the ratio of ED-spectra recorded at two different echo delays. The librational amplitude, ², was determined for a spin label at the 14-C position of the lipid chain from the partially motionally averaged hyperfine splitting in the conventional EPR spectra. The librational correlation time, _c, which is deduced from combination of the conventional and ED-EPR results, lies in the subnanosecond regime and depends only weakly on temperature. The temperature dependence of the ED-EPR spectra arises mainly from an increase in librational amplitude with increasing temperature, and position down the lipid chain. A gradual transition takes place at higher temperatures, from a situation in which segmental torsional librations are cumulative, i.e., the contributions of the individual segments add up progressively upon going down the chain, to one of concerted motion only weakly dependent on chain position. Such librational motions are important for glass-like states and are generally relevant to high lipid packing densities, e.g., in cholesterol-containing raft domains and condensed complexes.

This article has been cited by other articles:

				R. Bartucci, R. Guzzi, M. De Zotti, C. Toniolo, L. Sportelli, and D. Marsh Backbone Dynamics of Alamethicin Bound to Lipid Membranes: Spin-Echo Electron Paramagnetic Resonance of TOAC-Spin Labels Biophys. J., April 1, 2008; 94(7): 2698 - 2705. [Abstract] [Full Text] [PDF]