Structural and functional characterization of the nitrite channel NirC from Salmonella typhimurium
Structural and functional characterization of the nitrite channel NirC from Salmonella typhimurium
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DOI：
10.1073/pnas.1210793109
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发表时间：
2012-11-06
影响因子：
11.1
通讯作者：
Einsle, Oliver
中科院分区：
文献类型：
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作者：
Lu, Wei;Schwarzer, Nikola J.;Einsle, Oliver
亚硝酸盐（NO2-）是微生物和植物氮代谢的中心中间体，并被巨噬细胞用作细胞毒素，作为先天免疫反应的一部分。细菌膜蛋白NirC作为一种特异性通道，促进亚硝酸根阴离子跨脂质双层的运输，用于细胞质解毒。尽管NirC在氮代谢和肠道细菌致病性中的重要性，但可用的生化数据很少。在这里，我们提出了一个功能和结构表征的NIRC从鼠伤寒沙门氏菌的脂质双层电生理学和X射线晶体学。NirC是膜蛋白甲酸盐/亚硝酸盐转运蛋白家族的五聚体成员，其作为具有高电导的通道起作用。单通道测量揭示了快速和慢速门控事件，但与相关的福卡甲酸通道相反，没有pH依赖性门控。A 2.4埃的晶体结构的NirC在pH 5显示相似的福卡和水通道蛋白，但缺乏在甲酸盐通道中观察到的结构不对称性在同样低的pH值。解决的水分子在原聚体中建议的运输机制，也允许兼性NO2-/H+同向运输。
Nitrite (NO2-) is a central intermediate in the nitrogen metabolism of microorganisms and plants, and is used as a cytotoxin by macrophages as part of the innate immune response. The bacterial membrane protein NirC acts as a specific channel to facilitate the transport of nitrite anions across lipid bilayers for cytoplasmic detoxification. Despite NirC's importance in nitrogen metabolism and in the pathogenicity of enteric bacteria, available biochemical data are scarce. Here we present a functional and structural characterization of NirC from Salmonella typhimurium by lipid bilayer electrophysiology and X-ray crystallography. NirC is a pentameric member of the formate/nitrite transporter family of membrane proteins that operates as a channel with high conductance. Single-channel measurements reveal fast and slow gating events but, in contrast to the related FocA formate channel, no pH-dependent gating. A 2.4 angstrom crystal structure of NirC at pH 5 shows similarity to FocA and aquaporins, but lacks the structural asymmetry observed in the formate channel at similarly low pH. Resolved water molecules in the protomers suggest a transport mechanism that also permits a facultative NO2-/H+ symport.