Cys-loop receptors play important roles in signal transduction. The Gloeobacter ligand-gated ion channel (GLIC) pore binds similar compounds to Cys-loop receptor pores, but has the advantage of known structures in open and closed states. GLIC is activated by protons with a pEC₅₀ of 5.4, and has a histidine residue (His 11’) in its pore-forming α-helix (M2) which is involved in gating. Here we explore the role of this His and other M2 residues using two-electrode voltage clamp of mutant receptors expressed in oocytes. We show that 11’His is very sensitive to substitution; replacement with a range of amino acids ablates function. Similarly altering its location in M2 to the 8’, 9’, 10’, 12’, 13’ or 14’ positions ablated function. Most substitutions of Ser6’ or Ile9’ were also non-functional, although not Ile9’Leu and Ile9’Val. Unexpectedly, an Ile9’His substitution was constitutively active at pH 7, but closed as [H+] increased, with a pIC₅₀ of 5.8. Substitution at 2’, 5’ and 7’ had little effect on pEC₅₀. Overall the data show Ser6’ and His11’ are critical for the function of the receptor, and thus distinguish the roles of these M2 residues from those of Cys-loop receptors, where substitutions are mostly well tolerated. These data suggest modellers should be aware of these atypical features when using the GLIC pore as a model for Cys-loop receptor pores.

半胱氨酸环受体在信号转导中起重要作用。所述Gloeobacter配体门控离子通道（GLIC）孔隙结合类似的化合物，以半胱氨酸环受体孔，而是具有在打开和闭合状态已知的结构的优点。GLIC由质子激活p EC ₅₀5.4，并且在参与门控的成孔α-螺旋（M2）中具有组氨酸残基（His 11'）。在这里，我们使用卵母细胞中表达的突变受体的两电极电压钳位来探索此His和其他M2残基的作用。我们显示11'His对取代非常敏感；用一系列氨基酸替代具有消融功能。类似地，将其在M2中的位置更改为8'，9'，10'，12'，13'或14'位置可消除功能。尽管不是Ile9'Leu和Ile9'Val，Ser6'或Ile9'的大多数取代也是无功能的。出乎意料的是，Ile9'His取代在pH 7时具有组成性活性，但随着[H +]的增加而闭合，p IC ₅₀为5.8。2'，5'和7'处的取代对p EC ₅₀影响很小。总体而言，数据显示Ser6'和His11'对于受体的功能至关重要，因此可以将这些M2残基与Cys-loop受体的作用区分开，在Cys-loop受体中，对取代的耐受性最高。这些数据表明，在使用GLIC孔作为Cys-loop受体孔的模型时，建模者应该意识到这些非典型特征。