Phenylalanine in the Pore of the Erwinia Ligand-Gated Ion Channel Modulates Picrotoxinin Potency but Not Receptor Function

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• 作者：Andrew J. Thompson ; Mona Alqazzaz ; Kerry L. Price ; David A. Weston ; Sarah C. R. Lummis
• 刊名：Biochemistry
• 出版年：2014
• 出版时间：October 7, 2014
• 年：2014
• 卷：53
• 期：39
• 页码：6183-6188
• 全文大小：285K
• ISSN：1520-4995

文摘

The Erwinia ligand-gated ion channel (ELIC) is a bacterial homologue of eukaryotic Cys-loop ligand-gated ion channels. This protein has the potential to be a useful model for Cys-loop receptors but is unusual in that it has an aromatic residue (Phe) facing into the pore, leading to some predictions that this protein is incapable of ion flux. Subsequent studies have shown this is not the case, so here we probe the role of this residue by examining the function of the ELIC in cases in which the Phe has been substituted with a range of alternative amino acids, expressed in Xenopus oocytes and functionally examined. Most of the mutations have little effect on the GABA EC₅₀, but the potency of the weak pore-blocking antagonist picrotoxinin at F16鈥睞-, F16鈥睤-, F16鈥睸-, and F16鈥睺-containing receptors was increased to levels comparable with those of Cys-loop receptors, suggesting that this antagonist can enter the pore only when residue 16鈥?is small. T6鈥睸 has no effect on picrotoxinin potency when expressed alone but abolishes the increased potency when combined with F16鈥睸, indicating that the inhibitor binds at position 6鈥? as in Cys-loop receptors, if it can enter the pore. Overall, the data support the proposal that the ELIC pore is a good model for Cys-loop receptor pores if the role of F16鈥?is taken into consideration.