Rapid desensitization of the rat a7 nAChR is facilitated by the presence of a proline residue in the outer ß-sheet.
Rapid desensitization of the rat a7 nAChR is facilitated by the presence of a proline residue in the outer ß-sheet.
复制标题
外层β片中脯氨酸残基的存在促进了大鼠a7 nAChR的快速脱敏。
DOI：
10.1113/jphysiol.2010.195495
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
McCormack TJ
中科院分区：
文献类型：
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作者：
McCormack TJ
大鼠 α7 烟碱乙酰胆碱受体 (nAChR) 在 β9 链中部附近有一个脯氨酸残基。将 180 位 (P180) 的脯氨酸残基替换为苏氨酸 (α7-P180T) 或丝氨酸 (α7-P180S) 显着减慢了脱敏的发生，半衰期分别为 930 毫秒和 700 毫秒，而野生型受体的半衰期为 90 毫秒。为了研究 180 位侧链上羟基的重要性，对突变受体 α7-P180Y 和 α7-P180F 进行了研究，结果显示脱敏半衰期分别为 650 毫秒和 160 毫秒。虽然 180 位侧链 OH 基团可能会导致缓慢的脱敏率，但 α7-P180S 和 α7-P180V 导致受体具有相似的脱敏率，这表明在 180 位缺乏脯氨酸的情况下预期增加的主链与主链 H 键合可能会对脱敏产生巨大影响。单通道记录表明，对于 α7-P180T 受体，关闭时间显着缩短，单通道电导没有任何变化（与野生型相比）。动力学模拟表明，观察到的突变通道行为的所有变化都是通过降低脱敏率和增加与静息受体的微观亲和力来重现的。使用同源模型的分子动力学 (MD) 模拟来深入了解 P180 残基突变时外部 β 片层内可能发生的 H 键相互作用。所有分析的突变都使 180 位残基和 β10 链主链之间的 H 键数量增加了约两倍。此外，α7-P180T和α7-P180S突变也沿着β9链形成一些链内H键，尽管苏氨酸或丝氨酸侧链的OH基团的H键预计很少见。我们的结果表明，β9 链内脯氨酸残基的存在促进了野生型大鼠 α7 nAChR 的快速脱敏。
The rat α7 nicotinic acetylcholine receptor (nAChR) has a proline residue near the middle of the β9 strand. The replacement of this proline residue at position 180 (P180) by either threonine (α7‐P180T) or serine (α7‐P180S) slowed the onset of desensitization dramatically, with half‐times of ∼930 and 700 ms, respectively, compared to 90 ms for the wild‐type receptor. To investigate the importance of the hydroxyl group on the position 180 side‐chains, the mutant receptors α7‐P180Y and α7‐P180F were studied and showed half‐times of desensitization of 650 and 160 ms, respectively. While a position 180 side‐chain OH group may contribute to the slow desensitization rates, α7‐P180S and α7‐P180V resulted in receptors with similar desensitization rates, suggesting that increased backbone to backbone H bonding expected in the absence of proline at position 180 would likely exert a great effect on desensitization. Single channel recordings indicated that for the α7‐P180T receptor there was a significantly reduced closed time without any change in single channel conductance (as compared to wild‐type). Kinetic simulations indicated that all changes observed for the mutant channel behaviour were reproduced by decreasing the rate of desensitization, and increasing the microscopic affinity to resting receptors. Molecular dynamics (MD) simulations on a homology model were used to provide insight into likely H bond interactions within the outer β‐sheet that occur when the P180 residue is mutated. All mutations analysed increased about twofold the predicted number of H bonds between the residue at position 180 and the backbone of the β10 strand. Moreover, the α7‐P180T and α7‐P180S mutations also formed some intrastrand H bonds along the β9 strand, although H bonding of the OH groups of the threonine or serine side‐chains was predicted to be infrequent. Our results indicate that rapid desensitization of the wild‐type rat α7 nAChR is facilitated by the presence of the proline residue within the β9 strand.