Heiser Florian, Biedermann Johann, Kuru Ece, Plested Andrew J R, Sun Han
Department of Cellular Biophysics, Institute of Biology, Humboldt-Universität zu Berlin, Berlin 10117, Germany.
Research Unit of Structural Chemistry & Computational Biophysics, Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin 13156, Germany.
Proc Natl Acad Sci U S A. 2025 Aug 19;122(33):e2425172122. doi: 10.1073/pnas.2425172122. Epub 2025 Aug 14.
GluA2 is a key subunit of -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) ion channels that is abundantly expressed in the vertebrate brain. Posttranscriptional Q/R editing of GluA2 renders AMPARs nearly impermeable to calcium ions, which is crucial for their normal function. Although previous studies have characterized conductivity and selectivity differences between edited and unedited GluA2 variants and heteromeric receptors incorporating GluA2, the consequences of pore editing have not been studied in all-atom simulations, which leave the atomistic mechanisms unclear. In this study, we investigate ion permeation in the context of multiple Ca binding sites along the pore predicted from molecular dynamics (MD) simulations, considering both mutations and co-permeating monovalent ions. Patch clamp electrophysiology recordings confirmed a binding site at the intracellular mouth of the selectivity filter that confers selectivity for calcium over monovalent ions. A patient mutation at the same site has been previously shown to cause neurodevelopmental abnormalities. Furthermore, MD simulations of GluA2 with different arginine copy number at the Q/R site show that Ca conduction is blocked in the presence of two arginines, whereas K is only blocked by four arginines, in explaining the results from decades of electrophysiological work. Finally, MD simulations revealed that Ca reduces K conduction by preferentially occupying the intracellular selectivity filter binding site, whereas Na does not. This result is consistent with electrophysiological results from the D590 mutants and suggests that divalent binding in the selectivity filter is a major determinant of AMPAR conductance.
谷氨酸受体2（GluA2）是α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（AMPAR）离子通道的关键亚基，在脊椎动物大脑中大量表达。GluA2的转录后Q/R编辑使AMPAR对钙离子几乎不可渗透，这对其正常功能至关重要。尽管先前的研究已经描述了编辑和未编辑的GluA2变体以及包含GluA2的异源受体之间的电导率和选择性差异，但尚未在全原子模拟中研究孔编辑的后果，这使得原子机制尚不清楚。在本研究中，我们在分子动力学（MD）模拟预测的沿孔的多个钙结合位点的背景下研究离子渗透，同时考虑突变和共渗透单价离子。膜片钳电生理记录证实了选择性过滤器细胞内口处的一个结合位点，该位点赋予钙离子对单价离子的选择性。先前已证明同一部位的患者突变会导致神经发育异常。此外，在Q/R位点具有不同精氨酸拷贝数的GluA2的MD模拟表明，在存在两个精氨酸的情况下钙传导被阻断，而钾仅被四个精氨酸阻断，这解释了数十年电生理工作的结果。最后，MD模拟表明，钙通过优先占据细胞内选择性过滤器结合位点来降低钾传导，而钠则不会。这一结果与D590突变体的电生理结果一致，并表明选择性过滤器中的二价结合是AMPAR电导率的主要决定因素。
