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Publication Abstract from PubMed

Unlike classical voltage-gated sodium (Na(V)) channels, Na(X) has been characterized as a voltage-insensitive, tetrodotoxin-resistant, sodium (Na(+))-activated channel involved in regulating Na(+) homeostasis. However, Na(X) remains refractory to functional characterization in traditional heterologous systems. Here, to gain insight into its atypical physiology, we determine structures of the human Na(X) channel in complex with the auxiliary beta3-subunit. Na(X) reveals structural alterations within the selectivity filter, voltage sensor-like domains, and pore module. We do not identify an extracellular Na(+)-sensor or any evidence for a Na(+)-based activation mechanism in Na(X). Instead, the S6-gate remains closed, membrane lipids fill the central cavity, and the domain III-IV linker restricts S6-dilation. We use protein engineering to identify three pore-wetting mutations targeting the hydrophobic S6-gate that unlock a robust voltage-insensitive leak conductance. This constitutively active Na(X)-QTT channel construct is non-selective among monovalent cations, inhibited by extracellular calcium, and sensitive to classical Na(V) channel blockers, including tetrodotoxin. Our findings highlight a functional diversity across the Na(V) channel scaffold, reshape our understanding of Na(X) physiology, and provide a template to demystify recalcitrant ion channels.

Structure-guided unlocking of Na(X) reveals a non-selective tetrodotoxin-sensitive cation channel.,Noland CL, Chua HC, Kschonsak M, Heusser SA, Braun N, Chang T, Tam C, Tang J, Arthur CP, Ciferri C, Pless SA, Payandeh J Nat Commun. 2022 Mar 17;13(1):1416. doi: 10.1038/s41467-022-28984-4. PMID:35301303^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.