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Nat Commun. 2012 Apr 24;3:793. doi: 10.1038/ncomms1797.

The C-terminal helical bundle of the tetrameric prokaryotic sodium channel accelerates the inactivation rate.

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Department of Biophysics, Graduate School of Science, Kyoto University, Oiwake, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan.


Most tetrameric channels have cytosolic domains to regulate their functions, including channel inactivation. Here we show that the cytosolic C-terminal region of NavSulP, a prokaryotic voltage-gated sodium channel cloned from Sulfitobacter pontiacus, accelerates channel inactivation. The crystal structure of the C-terminal region of NavSulP grafted into the C-terminus of a NaK channel revealed that the NavSulP C-terminal region forms a four-helix bundle. Point mutations of the residues involved in the intersubunit interactions of the four-helix bundle destabilized the tetramer of the channel and reduced the inactivation rate. The four-helix bundle was directly connected to the inner helix of the pore domain, and a mutation increasing the rigidity of the inner helix also reduced the inactivation rate. These findings suggest that the NavSulP four-helix bundle has important roles not only in stabilizing the tetramer, but also in accelerating the inactivation rate, through promotion of the conformational change of the inner helix.

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