The membrane lateral pressure-perturbing capacity of parabens and their effects on the mechanosensitive channel directly correlate with hydrophobicity
The membrane lateral pressure-perturbing capacity of parabens and their effects on the mechanosensitive channel directly correlate with hydrophobicity
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DOI：
10.1021/bi801092g
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发表时间：
2008-10-07
期刊：
影响因子：
2.9
通讯作者：
Sukharev, Sergei
中科院分区：
文献类型：
--
作者：
Kamaraju, Kishore;Sukharev, Sergei
脂双层为膜蛋白提供了一个天然的各向异性环境，并可作为脂类衍生的第二信使或亲脂性药物的非极性储存库。亲脂性试剂的分配改变了双层中的侧压力分布，影响了整体蛋白质。对羟基苯甲酸酯(对羟基苯甲酸酯)是一类广泛用于食品和化妆品防腐剂的两亲性化合物，但其广泛的抗菌作用机理尚不清楚。在这里，我们描述了乙基、丙基和丁基对小电导细菌机械敏感通道(MSCs)门控的影响，并将它们与在这些物质存在时测得的脂单分子膜的表面活性和侧压变化进行了比较。在35mN/m的双层-单层等效压附近，对羟基苯甲酸乙酯、丙基或丁基对羟基苯甲酸酯存在于1 mm的亚相中，使单层的表面压力分别增加了5%、12.5%和20%。在膜片钳实验中，无论是胞质侧还是周质侧加入对羟基苯甲酸酯，均未观察到MSCs通道的自发激活。在切除贴片的细胞质一侧，浓度增加的对羟基苯甲酸酯使MSCs的激活曲线向更高的张力移动。膜片钳实验中单层压力的增加与激活中点的移动之间的良好相关性表明，疏水性越强的仿生物质越强烈地分配到脂质中，并通过改变侧向压力对通道门控产生更大的影响。我们发现细胞质中的乙基或丁基对羟基苯甲酸酯既加速了MSCs的脱敏过程，又不同程度地影响了失活。较高的脱敏率可能是由于门周围细胞质小叶的侧向压力增加所致。这两种蛋白都不会强烈影响MSCs的恢复率，也不能穿透MSCs中的TM2-TM3螺旋间隙。我们的结论是，细菌机械敏感通道MSCs提供了两亲性分子施加的侧膜压力的灵敏读数，但可能不是Parabens抗菌活性的主要靶点。
Lipid bilayers provide a natural anisotropic environment for membrane proteins and can serve as apolar reservoirs for lipid-derived second messengers or lipophilic drugs. Partitioning of lipophilic agents changes the lateral pressure distribution in the bilayer, affecting integral proteins. p-Hydroxybenzoic acid esters (parabens) are amphipathic compounds widely used as food and cosmetics preservatives, but the mechanisms of their broad antibacterial action are unknown. Here we describe effects of ethyl, propyl, and butyl parabens on the gating of the bacterial mechanosensitive channel of small conductance (MscS) and compare them with the surface activity and lateral pressure changes measured in lipid monolayers in the presence of these substances. Near the bilayer-monolayer equivalence pressure of 35 mN/m, ethyl, propyl, or butyl paraben present in the subphase at 1 mM increased the surface pressure of the monolayer by 5, 12.5, or 20%, respectively. No spontaneous activation of MscS channels was observed in patch-clamp experiments with parabens added from either the cytoplasmic or periplasmic side. Increasing concentrations of parabens on the cytoplasmic side of excised patches shifted activation curves of MscS toward higher tensions. A good correlation between the pressure increases in monolayers and shifts in activation midpoints in patch-clamp experiments suggested that the more hydrophobic parabens partition more strongly into the lipid and exert larger effects on channel gating through changes in lateral pressure. We show that cytoplasmically presented ethyl or butyl parabens both hasten the process of desensitization of MscS and influence inactivation differently. The higher rate of desensitization is likely due to increased lateral pressure in the cytoplasmic leaflet surrounding the gate. Neither of the parabens strongly affects the rate of recovery and does not seem to penetrate the TM2-TM3 interhelical clefts in MscS. We conclude that the bacterial mechanosensitive channel MscS provides a sensitive readout of lateral membrane pressure exerted by amphipathic molecules but may not be the primary target for the parabens in their antimicrobial activity.