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Prog Biophys Mol Biol. 2010 Sep;103(1):111-21. doi: 10.1016/j.pbiomolbio.2010.05.002. Epub 2010 May 26.

The C-terminal coiled-coil of the bacterial voltage-gated sodium channel NaChBac is not essential for tetramer formation, but stabilizes subunit-to-subunit interactions.

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Biomedicinal Information Research Center, National Institute of Advanced Industrial Science and Technology, Aomi 2-3-26, Koto-ku, Tokyo 135-0064, Japan.


The NaChBac is a prokaryotic homologue of the voltage-gated sodium channel found in the genome of the alkalophilic bacterium Bacillus halodurans C-125. Like a repeating cassette of mammalian sodium channel, the NaChBac possesses hydrophobic domains corresponding to six putative transmembrane segments and a pore loop, and exerts channel function by forming a tetramer although detailed mechanisms of subunit assembly remain unclear. We generated truncated mutants from NaChBac, and investigated their ability to form tetramers in relation to their channel functions. A mutant that deletes almost all of the C-terminal coiled-coil structure lost its voltage-dependent ion permeability, although it was properly translocated to the cell surface. The mutant protein was purified as a tetramer using a reduced concentration of detergent, but the association between the subunits was shown to be much weaker than the wild type. The chemical cross-linking, blue native PAGE, sedimentation velocity experiments, size exclusion chromatography, immunoprecipitation, and electron microscopy all supported its tetrameric assembly. We further purified the C-terminal cytoplasmic domain alone and confirmed its self-oligomerization. These data suggest that the C-terminal coiled-coil structure stabilizes subunit-to-subunit interactions of NaChBac, but is not critical for their tetramer formation.

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