biostudies-literatureNoland CLNovo Nordisk Fonden1416https://www.ebi.ac.uk/biostudies/studies/S-EPMC8931054biostudies-literatureUnknown13(1)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 β3-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 remaNature communicationsStructure-guided unlocking of Na_X reveals a non-selective tetrodotoxin-sensitive cation channel.PMC8931054NNF20OC0064550Tang JNoland CLCiferri CKschonsak MPless SAHeusser SABraun NChang TChua HCArthur CPPayandeh JTam CfalseStructure-guided unlocking of Na_X reveals a non-selective tetrodotoxin-sensitive cation channel.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 β3-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 rema2022-01-01T00:00:00Z2022 Mar2026-05-09T19:51:33.969Z2025-02-19T00:56:42.487ZS-EPMC89310543530130310.1038/s41467-022-28984-4