Article Dans Une Revue Analytical Chemistry Année : 2023

Dynamic Sorting of Mobile and Rigid Molecules in Biomembranes by Magic-Angle Spinning 13 C NMR

Résumé

Understanding the membrane dynamics of complex systems is essential to follow their function. As molecules in membranes can be in a rigid or mobile state depending on external (temperature, pressure) or internal (pH, domains, etc.) conditions, we propose an in-depth examination of NMR methods to filter highly mobile molecular parts from others that are in more restricted environments. We have thus developed a quantitative magic-angle spinning (MAS) 13C NMR approach coupled with cross-polarization (CP) and/or Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) on rigid and fluid unlabeled model membranes. We demonstrate that INEPT can detect only very mobile lipid headgroups in gel (solid-ordered) phases; the remaining rigid parts are only detected with CP. A direct correlation is established between the normalized line intensity as obtained by CP and the C–H (C–D) order parameters measured by wide-line 2H NMR or extracted from molecular dynamics: ICP/IDPeq ≈ 5|SCH|, indicating that when the order is greater than 0.2–0.3 (maximum value of 0.5 for chain CH2), only rigid parts can be filtered and detected using CP techniques. In very fluid (liquid-disordered) membranes, where there are many more active motions, both INEPT and CP detect resonances, with, however, a clear propensity of each technique to detect mobile and restricted molecular parts, respectively. Interestingly, the 13C NMR chemical shift of lipid hydrocarbon chains can be used to monitor order–disorder phase transitions and calculate the fraction of chain defects (rotamers) and the part of the transition enthalpy due to bond rotations (6–7 kJ·mol–1 for dimyristolphosphatidylcholine, DMPC). Cholesterol-containing membranes (liquid-ordered phases) can be dynamically contrasted as the rigid-body sterol is mainly detected by the CP technique, with a contact time of 1 ms, and the phospholipid by INEPT. Our work opens up a straightforward, robust, and cost-effective route for the determination of membrane dynamics by taking advantage of well-resolved conventional 13C NMR experiments without the need of isotopic labeling

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hal-04308708 , version 1 (27-11-2023)

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Estelle Morvan, Axelle Grélard, Antoine Loquet, Nada Taib-Maamar, Erick J Dufourc. Dynamic Sorting of Mobile and Rigid Molecules in Biomembranes by Magic-Angle Spinning 13 C NMR. Analytical Chemistry, 2023, 95 (7), pp.3596-3605. ⟨10.1021/acs.analchem.2c04185⟩. ⟨hal-04308708⟩
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