Proton-Binding Sites of Acid-Sensing Ion Channel 1
Proton-Binding Sites of Acid-Sensing Ion Channel 1
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DOI：
10.1371/journal.pone.0016920
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发表时间：
2011-02-14
期刊：
影响因子：
3.7
通讯作者：
Ishikita, Hiroshi
中科院分区：
文献类型：
--
作者：
Ishikita, Hiroshi
酸敏感离子通道（ASIC）是存在于哺乳动物中枢和外周神经系统的质子门控阳离子通道。ASIC 1是所有ASIC中最丰富的，并且可能调节突触传递。确定ASCI 1的质子结合位点是阐明其pH敏感机制所必需的。通过使用ASIC 1的晶体结构，通过在所有这些位点的质子化状态同时处于平衡的条件下求解泊松-玻尔兹曼方程来计算ASIC 1的每个可滴定位点的质子化状态。发现四个酸性-酸性残基对-Asp 238-Asp 350、Glu 220-Asp 408、Glu 239-Asp 346和Glu 80-Glu 417-被高度质子化。特别是内孔中的Glu 80-Glu 417对被完全质子化并具有2 H（+），这意味着其可能作为质子结合位点的重要性。Glu 239的pK（a）与可能的pH敏感位点Asp 346形成一对，由于亚基的不同蛋白质构象中Thr 237的不同氢键模式，每个同源三聚体亚基之间不同。His 74的pK（a）值约为6-7。His 74在质子敏感ASIC 3中的保守性缺乏对应于Asp 346的残基，这可能表明其在质子敏感ASIC中可能的pH传感作用。
Acid-sensing ion channels (ASICs) are proton-gated cation channels that exist throughout the mammalian central and peripheral nervous systems. ASIC1 is the most abundant of all the ASICs and is likely to modulate synaptic transmission. Identifying the proton-binding sites of ASCI1 is required to elucidate its pH-sensing mechanism. By using the crystal structure of ASIC1, the protonation states of each titratable site of ASIC1 were calculated by solving the Poisson-Boltzmann equation under conditions wherein the protonation states of all these sites are simultaneously in equilibrium. Four acidic-acidic residue pairs-Asp238-Asp350, Glu220-Asp408, Glu239-Asp346, and Glu80-Glu417-were found to be highly protonated. In particular, the Glu80-Glu417 pair in the inner pore was completely protonated and possessed 2 H(+), implying its possible importance as a proton-binding site. The pK(a) of Glu239, which forms a pair with a possible pH-sensing site Asp346, differs among each homo-trimer subunit due to the different H-bond pattern of Thr237 in the different protein conformations of the subunits. His74 possessed a pK(a) of similar to 6-7. Conservation of His74 in the proton-sensitive ASIC3 that lacks a residue corresponding to Asp346 may suggest its possible pH-sensing role in proton-sensitive ASICs.