An Ion Selectivity Filter in the Extracellular Domain of Cys-loop Receptors Reveals Determinants for Ion Conductance
An Ion Selectivity Filter in the Extracellular Domain of Cys-loop Receptors Reveals Determinants for Ion Conductance
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DOI：
10.1074/jbc.c800194200
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发表时间：
2008-12-26
影响因子：
4.8
通讯作者：
Sine, Steven M.
中科院分区：
文献类型：
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作者：
Hansen, Scott B.;Wang, Hai-Long;Sine, Steven M.
神经递质与cys环受体结合可促进数百万离子/秒的巨大跨膜通量，但迄今为止，已确定离子通量的结构决定因素位于跨膜区域的两侧。利用x射线晶体学、序列分析和单通道记录，我们在渗透离子进入点附近发现了一种新的离子电导决定因素。乙酰胆碱结合蛋白与硫酸盐阴离子的共结晶表明，在同源Cys-loop受体中，SO42-与相当于脂膜上方24a位置的赖氨酸环配位。多个序列比对分析表明，赖氨酸环等效残基在阳离子选择性受体中带负电荷，而在阴离子选择性受体中带正电荷。来自运动端板的烟碱受体中同源位置侧链的电荷反转可使单位电导降低高达80%。选择性过滤器源于跨膜α -螺旋具有相似的孔径和氨基酸组成。这些发现表明，当通道在生理电化学梯度下打开时，渗透离子最初在Cys-loop受体的细胞外前庭内稳定，这种稳定是离子电导率的主要决定因素。
Neurotransmitter binding to Cys-loop receptors promotes a prodigious transmembrane flux of several million ions/s, but to date, structural determinants of ion flux have been identified flanking the membrane-spanning region. Using x-ray crystallography, sequence analysis, and single-channel recording, we identified a novel determinant of ion conductance near the point of entry of permeant ions. Co-crystallization of acetylcholine-binding protein with sulfate anions revealed coordination of SO42- with a ring of lysines at a position equivalent to 24 A above the lipid membrane in homologous Cys-loop receptors. Analysis of multiple sequence alignments revealed that residues equivalent to the ring of lysines are negatively charged in cation-selective receptors but are positively charged in anion-selective receptors. Charge reversal of side chains at homologous positions in the nicotinic receptor from the motor end plate decreases unitary conductance up to 80%. Selectivity filters stemming from transmembrane alpha-helices have similar pore diameters and compositions of amino acids. These findings establish that when the channel opens under a physiological electrochemical gradient, permeant ions are initially stabilized within the extracellular vestibule of Cys-loop receptors, and this stabilization is a major determinant of ion conductance.