De Planque Maurits R R, Rijkers Dirk T S, Liskamp Rob M J, Separovic Frances
School of Chemistry, University of Melbourne, Melbourne, Victoria 3010, Australia.
Magn Reson Chem. 2004 Feb;42(2):148-54. doi: 10.1002/mrc.1326.
The transmembrane domain of the nicotinic acetylcholine receptor (nAChR) plays a role in the regulation of the activity of this important ligand-gated ion channel. The lipid composition of the host membrane affects conformational equilibria of the nAChR and several classes of inhibitors, most notably anaesthetics, interact directly or indirectly with the four transmembrane M-segments, M1-M4, of the nAChR subunits. It has proven difficult to gain insight into structure-function relationships of the M-segments in the context of the entire receptor and the biomembrane environment. However, model membrane systems are well suited to obtain detailed information about protein-lipid interactions. In this solid-state NMR study, we characterized interactions between a synthetic alphaM1 segment of the T. californica nAChR and model membranes of different phosphatidylcholine (PC) lipids. The results indicate that alphaM1 interacts strongly with PC bilayers: the peptide orders the lipid acyl chains and induces the formation of small vesicles, possibly through modification of the lateral pressure profile in the bilayer. The multilamellar vesicle morphology was stabilized by the presence of cholesterol, implying that either the rigidity or the bilayer thickness is a relevant parameter for alphaM1-membrane interactions, which also has been suggested for the entire nAChR. Our results suggest that the model systems are to a certain extent sensitive to peptide-bilayer hydrophobic matching requirements, but that the lipid response to hydrophobic mismatch alone is not the explanation. The effect of alphaM1 on different PC bilayers may indicate that the peptide is conformationally flexible, which in turn would support a membrane-mediated modulation of the conformation of transmembrane segments of the nAChR.
烟碱型乙酰胆碱受体（nAChR）的跨膜结构域在调节这一重要的配体门控离子通道的活性中发挥作用。宿主膜的脂质组成会影响nAChR的构象平衡，并且几类抑制剂，最显著的是麻醉剂，会直接或间接与nAChR亚基的四个跨膜M片段（M1 - M4）相互作用。事实证明，在整个受体和生物膜环境的背景下深入了解M片段的结构 - 功能关系是困难的。然而，模型膜系统非常适合获取有关蛋白质 - 脂质相互作用的详细信息。在这项固态核磁共振研究中，我们表征了加州电鳐nAChR的合成αM1片段与不同磷脂酰胆碱（PC）脂质的模型膜之间的相互作用。结果表明，αM1与PC双层强烈相互作用：该肽使脂质酰基链有序排列，并可能通过改变双层中的侧向压力分布诱导小囊泡的形成。胆固醇的存在稳定了多层囊泡形态，这意味着刚性或双层厚度是αM1 - 膜相互作用的一个相关参数，这一点对于整个nAChR也有提及。我们的结果表明，模型系统在一定程度上对肽 - 双层疏水匹配要求敏感，但仅脂质对疏水不匹配的反应并不能解释这一现象。αM1对不同PC双层的影响可能表明该肽在构象上具有灵活性，这反过来又支持膜介导的nAChR跨膜片段构象的调节。
