Interaction of Spin-Labeled Lipid Membranes with Transition Metal Ions.
Interaction of Spin-Labeled Lipid Membranes with Transition Metal Ions.
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DOI：
10.1021/acs.jpcb.5b08165
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发表时间：
2015-10-22
期刊：
影响因子：
--
通讯作者：
Freed J
中科院分区：
文献类型：
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作者：
Dzikovski B;Livshits V;Freed J
溶解在水相中的顺磁性金属盐诱导的磷脂膜中的PC自旋标签的自旋弛豫增强（RE）的大值可以解释为海森堡自旋交换由于作为膜流动性的结果的氮氧基团的构象波动，脂质链的灵活性，以及可能的，氮氧标签的两亲性。无论磁性相互作用主要通过海森堡自旋交换（Ni）或偶极-偶极（Gd）机制发生，顺磁性离子都必须紧密靠近氮氧部分以实现有效的RE。对于不同的镍盐的RE在磷脂酰胆碱膜遵循阴离子Hofmeister系列，并反映阴离子吸附，然后由阴离子驱动的吸引力的顺磁性阳离子的胆碱基团。这种吸附对于离液离子更高，例如，高氯酸盐（离液剂是水溶液中的分子，其可以破坏水分子之间的氢键网络。然而，有没有阴离子的依赖性RE的模型膜从带负电荷的脂质缺乏胆碱基团。我们使用Ni诱导RE研究离子/膜相互作用的热力学和静电学。我们还研究了膜组成和相态对RE值的影响。在含有胆固醇的膜中，观察到具有足够长的氮氧自由基链的PC标记与不足以深入融合胆固醇环区域后面的膜疏水核心的PC标记之间存在显着差异。这项研究表明，必须谨慎解释PC标签在流体膜中获得的数据在不同的浸没深度探测膜性能时，它可以在膜表面的顺磁性物质的影响。
The large values of spin relaxation enhancement (RE) for PC spin-labels in the phospholipid membrane induced by paramagnetic metal salts dissolved in the aqueous phase can be explained by Heisenberg spin exchange due to conformational fluctuations of the nitroxide group as a result of membrane fluidity, flexibility of lipid chains, and, possibly, amphiphilic nature of the nitroxide label. Whether the magnetic interaction occurs predominantly via Heisenberg spin exchange (Ni) or by the dipole–dipole (Gd) mechanism, it is essential for the paramagnetic ion to get into close proximity to the nitroxide moiety for efficient RE. For different salts of Ni the RE in phosphatidylcholine membranes follows the anionic Hofmeister series and reflects anion adsorption followed by anion-driven attraction of paramagnetic cations on the choline groups. This adsorption is higher for chaotropic ions, e.g., perchlorate. (A chaotropic agent is a molecule in water solution that can disrupt the hydrogen bonding network between water molecules.) However, there is no anionic dependence of RE for model membranes made from negatively charged lipids devoid of choline groups. We used Ni-induced RE to study the thermodynamics and electrostatics of ion/membrane interactions. We also studied the effect of membrane composition and the phase state on the RE values. In membranes with cholesterol a significant difference is observed between PC labels with nitroxide tethers long enough vs not long enough to reach deep into the membrane hydrophobic core behind the area of fused cholesterol rings. This study indicates one must be cautious in interpreting data obtained by PC labels in fluid membranes in terms of probing membrane properties at different immersion depths when it can be affected by paramagnetic species at the membrane surface.