Specificity of cholesterol and analogs to modulate BK channels points to direct sterol-channel protein interactions
Specificity of cholesterol and analogs to modulate BK channels points to direct sterol-channel protein interactions
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DOI：
10.1085/jgp.201010519
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发表时间：
2011-01-01
影响因子：
3.8
通讯作者：
Dopico, Alex M.
中科院分区：
文献类型：
--
作者：
Bukiya, Anna N.;Belani, Jitendra D.;Dopico, Alex M.
大电导电压/Ca 2+门控K+（BK）通道的活性（Po）在天然膜中发现的范围内被胆固醇水平钝化。我们探测了BK通道形成α（cbv 1）亚基与胆固醇和相关的单羟基甾醇磷脂双层，并进行计算动力学，以确定单羟基甾醇的结构要求，以减少BK Po和获得深入了解胆固醇的作用机制。胆固醇，胆甾烷醇，粪甾烷醇减少PO缩短平均开放和延长平均关闭时间，而epicholesterol，epicholestanol，epicoprostanol，胆固醇trisnorcholenic酸是无效的。因此，单羟基甾醇的通道抑制需要C3羟基的β构型，并且侧链的疏水性质有利于通道抑制，同时对甾醇A/B环融合的要求不严格。BK通道开放状态的不稳定先前被解释为反映胆固醇增加的双层横向应力。侧向应力由固醇分子面积和脂质单层侧向张力控制，后者与固醇在脂质介质中采用平面构象的能力有关。然而，我们发现单羟基甾醇降低Po的不同功效（胆固醇>=粪甾烷醇>=胆甾烷醇>表胆甾醇）不遵循分子面积等级（粪甾烷醇>>表胆甾醇>胆固醇>胆甾烷醇）。此外，胆固醇（有效的BK抑制剂）和表胆固醇（无效）采用平面构象的计算预测能量是相似的。最后，胆固醇和粪甾烷醇减少宝，但这些甾醇有相反的效果，紧密的脂质包装，并可能，对横向应力。总的来说，这些研究结果表明，双层横向应力的增加是不太可能的基础的胆固醇和相关的类固醇抑制BK通道的能力差异。值得注意的是，ent-胆固醇（胆固醇镜像）未能降低Po，表明胆固醇功效需要蛋白质表面的固醇立体特异性识别。BK通道表型类似于α同四聚体的表型。因此，我们假设胆固醇识别蛋白质表面位于BK α亚基本身。
The activity (Po) of large-conductance voltage/Ca2+-gated K+ (BK) channels is blunted by cholesterol levels within the range found in natural membranes. We probed BK channel-forming alpha (cbv1) subunits in phospholipid bilayers with cholesterol and related monohydroxysterols and performed computational dynamics to pinpoint the structural requirements for monohydroxysterols to reduce BK Po and obtain insights into cholesterol's mechanism of action. Cholesterol, cholestanol, and coprostanol reduced Po by shortening mean open and lengthening mean closed times, whereas epicholesterol, epicholestanol, epicoprostanol, and cholesterol trisnorcholenic acid were ineffective. Thus, channel inhibition by monohydroxysterols requires the beta configuration of the C3 hydroxyl and is favored by the hydrophobic nature of the side chain, while having lax requirements on the sterol A/B ring fusion. Destabilization of BK channel open state(s) has been previously interpreted as reflecting increased bilayer lateral stress by cholesterol. Lateral stress is controlled by the sterol molecular area and lipid monolayer lateral tension, the latter being related to the sterol ability to adopt a planar conformation in lipid media. However, we found that the differential efficacies of monohydroxysterols to reduce Po (cholesterol >= coprostanol >= cholestanol>>>epicholesterol) did not follow molecular area rank (coprostanol>>epicholesterol>cholesterol>cholestanol). In addition, computationally predicted energies for cholesterol (effective BK inhibitor) and epicholesterol (ineffective) to adopt a planar conformation were similar. Finally, cholesterol and coprostanol reduced Po, yet these sterols have opposite effects on tight lipid packing and, likely, on lateral stress. Collectively, these findings suggest that an increase in bilayer lateral stress is unlikely to underlie the differential ability of cholesterol and related steroids to inhibit BK channels. Remarkably, ent-cholesterol (cholesterol mirror image) failed to reduce Po, indicating that cholesterol efficacy requires sterol stereospecific recognition by a protein surface. The BK channel phenotype resembled that of alpha homotetramers. Thus, we hypothesize that a cholesterol-recognizing protein surface resides at the BK alpha subunit itself.