期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 109, 期 45, 页码 18395-18400出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1210793109
关键词
ion channels; protein crystallography; planar lipid bilayer
资金
- Deutsche Forschungsgemeinschaft [Ei 520/3, Ei 520/6, An 676/1]
- International Research Training Grant [1478]
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.
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