Cryo-EM structures of the TMEM16A calcium-activated chloride channel.
Cryo-EM structures of the TMEM16A calcium-activated chloride channel.
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DOI：
10.1038/nature25024
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发表时间：
2017-12-21
期刊：
影响因子：
64.8
通讯作者：
Jan LY
中科院分区：
文献类型：
--
作者：
Dang S;Feng S;Tien J;Peters CJ;Bulkley D;Lolicato M;Zhao J;Zuberbühler K;Ye W;Qi L;Chen T;Craik CS;Jan YN;Minor DL Jr;Cheng Y;Jan LY
由TMEM 16 A编码的钙激活氯离子通道（CaCC）控制神经元信号传导、平滑肌收缩、气道和外分泌腺分泌以及胃肠系统的节律性运动。为了了解CaCC如何介导和控制阴离子渗透以实现这些生理功能，了解哺乳动物TMEM 16 A结构并鉴定其孔衬残基是必不可少的。TMEM 16 A形成具有两个孔的二聚体。以前的CaCC结构分析依赖于同源物（nhTMEM 16）的同源性建模，从真菌赤壳菌，主要作为一种脂质乱序酶，，以及亚纳米分辨率的电子冷冻显微镜。在这里，我们提出了novoatomic结构的小鼠TMEM 16 A的跨膜结构域的纳米盘和月桂基麦芽糖新戊二醇，确定通过单粒子电子冷冻显微镜。这些结构揭示了离子渗透孔并代表不同的功能状态。月桂基麦芽糖新戊二醇中的结构具有一个Ca 2+离子，其在具有收缩孔的每个单体内解析;这可能对应于封闭状态，因为具有单个Ca 2+占据的CaCO 3需要膜去极化以打开（C.J.P.et al.，手稿提交）。纳米盘中的结构每个单体具有两个Ca 2+离子，并且其孔处于闭合构象;这可能反映了通道衰减，这是在ImM Ca 2+中延长的CaCC活化之后通道活性的逐渐丧失。我们的诱变和电生理学研究，提示的结构分析，确定了10个残基分布沿着孔与渗透阴离子相互作用，影响阴离子的选择性，以及7个孔内衬残基附近的孔收缩和调节通道门控集群。总之，这些结果阐明了CaCO 3阴离子传导的基础。
Calcium-activated chloride channels (CaCCs) encoded by TMEM16A,,control neuronal signalling, smooth muscle contraction, airway and exocrine gland secretion, and rhythmic movements of the gastrointestinal system,,,. To understand how CaCCs mediate and control anion permeation to fulfil these physiological functions, knowledge of the mammalian TMEM16A structure and identification of its pore-lining residues are essential. TMEM16A forms a dimer with two pores,. Previous CaCC structural analyses have relied on homology modelling of a homologue (nhTMEM16) from the fungusNectria haematococcathat functions primarily as a lipid scramblase,,, as well as subnanometre-resolution electron cryo-microscopy. Here we presentde novoatomic structures of the transmembrane domains of mouse TMEM16A in nanodiscs and in lauryl maltose neopentyl glycol as determined by single-particle electron cryo-microscopy. These structures reveal the ion permeation pore and represent different functional states. The structure in lauryl maltose neopentyl glycol has one Ca2+ion resolved within each monomer with a constricted pore; this is likely to correspond to a closed state, because a CaCC with a single Ca2+occupancy requires membrane depolarization in order to open (C.J.P.et al., manuscript submitted). The structure in nanodiscs has two Ca2+ions per monomer and its pore is in a closed conformation; this probably reflects channel rundown, which is the gradual loss of channel activity that follows prolonged CaCC activation in 1 mM Ca2+. Our mutagenesis and electrophysiological studies, prompted by analyses of the structures, identified ten residues distributed along the pore that interact with permeant anions and affect anion selectivity, as well as seven pore-lining residues that cluster near pore constrictions and regulate channel gating. Together, these results clarify the basis of CaCC anion conduction.
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