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J Gen Physiol. 2018 Dec 3. pii: jgp.201711884. doi: 10.1085/jgp.201711884. [Epub ahead of print]

Molecular dissection of multiphase inactivation of the bacterial sodium channel NaVAb.

Author information

1
Department of Pharmacology, University of Washington, Seattle, WA.
2
Division of General Internal Medicine, Department of Medicine, University of Washington, Seattle, WA.
3
École Normal Supérieure, Cachan, France.
4
Howard Hughes Medical Institute, University of Washington, Seattle, WA.
5
Department of Pharmacology, University of Washington, Seattle, WA wcatt@uw.edu.

Abstract

Homotetrameric bacterial voltage-gated sodium channels share major biophysical features with their more complex eukaryotic counterparts, including a slow-inactivation mechanism that reduces ion-conductance activity during prolonged depolarization through conformational changes in the pore. The bacterial sodium channel NaVAb activates at very negative membrane potentials and inactivates through a multiphase slow-inactivation mechanism. Early voltage-dependent inactivation during one depolarization is followed by late use-dependent inactivation during repetitive depolarization. Mutations that change the molecular volume of Thr206 in the pore-lining S6 segment can enhance or strongly block early voltage-dependent inactivation, suggesting that this residue serves as a molecular hub controlling the coupling of activation to inactivation. In contrast, truncation of the C-terminal tail enhances the early phase of inactivation yet completely blocks late use-dependent inactivation. Determination of the structure of a C-terminal tail truncation mutant and molecular modeling of conformational changes at Thr206 and the S6 activation gate led to a two-step model of these gating processes. First, bending of the S6 segment, local protein interactions dependent on the size of Thr206, and exchange of hydrogen-bonding partners at the level of Thr206 trigger pore opening followed by the early phase of voltage-dependent inactivation. Thereafter, conformational changes in the C-terminal tail lead to late use-dependent inactivation. These results have important implications for the sequence of conformational changes that lead to multiphase inactivation of NaVAb and other sodium channels.

PMID:
30510035
DOI:
10.1085/jgp.201711884

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