Chemical substitutions in the selectivity filter of potassium channels do not rule out constricted-like conformations for C-type inactivation
Chemical substitutions in the selectivity filter of potassium channels do not rule out constricted-like conformations for C-type inactivation
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DOI：
10.1073/pnas.1706983114
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发表时间：
2017-10-17
影响因子：
11.1
通讯作者：
Roux, Benoit
中科院分区：
文献类型：
--
作者：
Li, Jing;Ostmeyer, Jared;Roux, Benoit
在许多K+通道中，长时间的激活刺激导致离子传导的时间依赖性降低，这种现象称为C型失活。KcsA通道的X射线结构表明，这种失活状态对应于选择性过滤器的“收缩”构象。然而，收缩构象的功能意义已成为一个有争议的问题。基于化学修饰的半合成KcsA通道沿着选择性过滤器的功能和结构研究得出的结论是，收缩的构象不对应于C型失活状态。支持这一观点的主要结果包括观察到Gly 77处的D-丙氨酸取代不抑制C型失活，即使这种修饰被认为将选择性过滤器锁定在其导电构象中，而Gly 77和Tyr 78处的酰胺至酯骨架取代后，C型失活被抑制，即使这些结构保守的修饰被认为不会阻止选择性过滤器采用收缩构象。然而，这些化学修饰的结构和功能影响的几个未经检验的假设，这些论点的基础。为了取得进展，进行了基于KcsA通道的原子模型的分子动力学模拟。计算结果支持这样的观点：选择性过滤器的收缩构象对应于KcsA的功能性C型失活状态。重要的是，MD模拟表明，半合成KcsA（D-ala 77）通道可以采用不对称的收缩样非导电构象，酰胺到酯骨架取代Gly 77和Tyr 78扰乱氢键，涉及埋水分子稳定收缩构象。
In many K+ channels, prolonged activating stimuli lead to a time-dependent reduction in ion conduction, a phenomenon known as C-type inactivation. X-ray structures of the KcsA channel suggest that this inactivated state corresponds to a "constricted" conformation of the selectivity filter. However, the functional significance of the constricted conformation has become a matter of debate. Functional and structural studies based on chemically modified semisynthetic KcsA channels along the selectivity filter led to the conclusion that the constricted conformation does not correspond to the C-type inactivated state. The main results supporting this view include the observation that C-type inactivation is not suppressed by a substitution of D-alanine at Gly77, even though this modification is believed to lock the selectivity filter into its conductive conformation, whereas it is suppressed following amide-to-ester backbone substitutions at Gly77 and Tyr78, even though these structure-conserving modifications are not believed to prevent the selectivity filter from adopting the constricted conformation. However, several untested assumptions about the structural and functional impact of these chemical modifications underlie these arguments. To make progress, molecular dynamics simulations based on atomic models of the KcsA channel were performed. The computational results support the notion that the constricted conformation of the selectivity filter corresponds to the functional C-type inactivated state of the KcsA. Importantly, MD simulations reveal that the semisynthetic KcsA(D-ala77) channel can adopt an asymmetrical constricted-like nonconductive conformation and that the amide-to-ester backbone substitutions at Gly77 and Tyr78 perturb the hydrogen bonding involving the buried water molecules stabilizing the constricted conformation.