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High-resolution structures illuminate key principles underlying voltage and LRRC26 regulation of Slo1 channels
Preprint   Open access

High-resolution structures illuminate key principles underlying voltage and LRRC26 regulation of Slo1 channels

Gopal S Kallure, Kamalendu Pal, Yu Zhou, Christopher J Lingle and Sandipan Chowdhury
bioRxiv : the preprint server for biology
Cold Spring Harbor laboratory
12/20/2023
DOI: 10.1101/2023.12.20.572542
PMCID: PMC10769243
PMID: 38187713
url
https://doi.org/10.1101/2023.12.20.572542View
Preprint (Author's original)This preprint has not been evaluated by subject experts through peer review. Preprints may undergo extensive changes and/or become peer-reviewed journal articles. Open Access

Abstract

Multi-modal regulation of Slo1 channels by membrane voltage, intracellular calcium, and auxiliary subunits enables its pleiotropic physiological functions. Our understanding of how voltage impacts Slo1 conformational dynamics and the mechanisms by which auxiliary subunits, particularly of the LRRC (Leucine Rich Repeat containing) family of proteins, modulate its voltage gating remain unresolved. Here, we used single particle cryo-electron microscopy to determine structures of human Slo1 mutants which functionally stabilize the closed pore (F315A) or the activated voltage-sensor (R207A). Our structures, obtained under calcium-free conditions, reveal that a key step in voltage-sensing by Slo1 involves a rotameric flip of the voltage-sensing charges (R210 and R213) moving them by ∼6 Å across a hydrophobic gasket. Next we obtained reconstructions of a complex of human Slo1 with the human LRRC26 (γ1) subunit in absence of calcium. Together with extensive biochemical tests, we show that the extracellular domains of γ1 form a ring of interlocked dominos that stabilizes the quaternary assembly of the complex and biases Slo1:γ1 assembly towards high stoichiometric complexes. The transmembrane helix of γ1 is kinked and tightly packed against the Slo1 voltage-sensor. We hypothesize that γ1 subunits exert relatively small effects on early steps in voltage-gating but structurally stabilize non-S4 helices of Slo1 voltage-sensor which energetically facilitate conformational rearrangements that occur late in voltage stimulated transitions.

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