AUTHOR=Bartucci Rosa , Aloi Erika 

TITLE=Librational Dynamics of Spin-Labeled Membranes at Cryogenic Temperatures From Echo-Detected ED-EPR Spectra

JOURNAL=Frontiers in Molecular Biosciences

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2022.923794

DOI=10.3389/fmolb.2022.923794

ISSN=2296-889X

ABSTRACT=<p>Methods of electron spin echo of pulse electron paramagnetic resonance (EPR) spectroscopy are increasingly employed to investigate biophysical properties of nitroxide-labeled biosystems at cryogenic temperatures. Two-pulse echo-detected ED-spectra have proven to be valuable tools to describe the librational dynamics in the low-temperature phases of both lipids and proteins in membranes. The motional parameter, <inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>α</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:msub><mml:mi>τ</mml:mi><mml:mi>C</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>, given by the product of the mean-square angular amplitude, <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>α</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math></inline-formula>, and the rotational correlation time, <inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>τ</mml:mi><mml:mi>C</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula>, of the motion, is readily determined from the nitroxide ED-spectra as well as from the <italic>W</italic>-relaxation rate curves. An independent evaluation of <inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>α</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math></inline-formula> is obtained from the motionally averaged <sup>14</sup>N-hyperfine splitting separation in the continuous wave cw-EPR spectra. Finally, the rotational correlation time <inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>τ</mml:mi><mml:mi>C</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> can be estimated by combining ED- and cw-EPR data. In this mini-review, results on the librational dynamics in model and natural membranes are illustrated.</p>