Highly Conserved Salt Bridge Stabilizes Rigid Signal Patch at Extracellular Loop Critical for Surface Expression of Acid-sensing Ion Channels*
Highly Conserved Salt Bridge Stabilizes Rigid Signal Patch at Extracellular Loop Critical for Surface Expression of Acid-sensing Ion Channels*
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DOI：
10.1074/jbc.m111.334250
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发表时间：
2012-03
期刊：
影响因子：
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通讯作者：
Yang Yang-Yang;Ye Yu;Jin Cheng;Yan Liu;Di-Shi Liu;Jin Wang;M. Zhu;Rui Wang;Tian-Le Xu
中科院分区：
文献类型：
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作者：
Yang Yang-Yang;Ye Yu;Jin Cheng;Yan Liu;Di-Shi Liu;Jin Wang;M. Zhu;Rui Wang;Tian-Le Xu
Background: Plasma membrane expression is vital for the function of ASICs, which act as extracellular proton sensors. Results: Mutations in a conserved salt bridge and its adjacent region impaired cell surface ASIC expression. Conclusion: Surface ASIC expression involves an exposed rigid signal patch at the extracellular loop. Significance: This finding sheds lights on new strategies to prevent excessive neuronal excitability associated with ASIC activation. Acid-sensing ion channels (ASICs) are non-selective cation channels activated by extracellular acidosis associated with many physiological and pathological conditions. A detailed understanding of the mechanisms that govern cell surface expression of ASICs, therefore, is critical for better understanding of the cell signaling under acidosis conditions. In this study, we examined the role of a highly conserved salt bridge residing at the extracellular loop of rat ASIC3 (Asp107-Arg153) and human ASIC1a (Asp107-Arg160) channels. Comprehensive mutagenesis and electrophysiological recordings revealed that the salt bridge is essential for functional expression of ASICs in a pH sensing-independent manner. Surface biotinylation and immunolabeling of an extracellular epitope indicated that mutations, including even minor alterations, at the salt bridge impaired cell surface expression of ASICs. Molecular dynamics simulations, normal mode analysis, and further mutagenesis studies suggested a high stability and structural constrain of the salt bridge, which serves to separate an adjacent structurally rigid signal patch, important for surface expression, from a flexible gating domain. Thus, we provide the first evidence of structural requirement that involves a stabilizing salt bridge and an exposed rigid signal patch at the destined extracellular loop for normal surface expression of ASICs. These findings will allow evaluation of new strategies aimed at preventing excessive excitability and neuronal injury associated with tissue acidosis and ASIC activation.
