Topography and motion of acid-sensing ion channel intracellular domains.

Tyler Couch,Tyler W McCullock,David M Maclean,Paul Kammermeier,Kyle D Berger,Dana L Kneisley

doi:10.7554/elife.68955

Tyler Couch, Tyler W McCullock + Show 4 more

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https://doi.org/10.7554/elife.68955

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Abstract

Acid-sensing ion channels (ASICs) are trimeric cation-selective channels activated by decreases in extracellular pH. The intracellular N and C terminal tails of ASIC1 influence channel gating, trafficking, and signaling in ischemic cell death. Despite several X-ray and cryo-EM structures of the extracellular and transmembrane segments of ASIC1, these important intracellular tails remain unresolved. Here, we describe the coarse topography of the chicken ASIC1 intracellular domains determined by fluorescence resonance energy transfer (FRET), measured using either fluorescent lifetime imaging or patch clamp fluorometry. We find the C terminal tail projects into the cytosol by approximately 35 Å and that the N and C tails from the same subunits are closer than adjacent subunits. Using pH-insensitive fluorescent proteins, we fail to detect any relative movement between the N and C tails upon extracellular acidification but do observe axial motions of the membrane proximal segments toward the plasma membrane. Taken together, our study furnishes a coarse topographic map of the ASIC intracellular domains while providing directionality and context to intracellular conformational changes induced by extracellular acidification.

Highlights

The predominant sensor of extracellular pH in the central and peripheral nervous system is thought to be acid-sensing ion channels (ASICs) (Pattison et al, 2019)
Extracellular acidosis is proposed to drive the association of the serine/threonine kinase receptor interacting protein 1 (RIP1) and N-ethylmaleimide-sensitive factor (NSF)
It is likely that the ASIC intracellular domains (ICDs) are partly, or even mostly, unstructured regions

Summary

Introduction

The predominant sensor of extracellular pH in the central and peripheral nervous system is thought to be acid-sensing ion channels (ASICs) (Pattison et al, 2019). ASICs join a growing, and controversial, list of ligand-gated ion channels who possess metabotropic signaling capacity (Dore et al, 2017; Kabbani and Nichols, 2018; Pressey and Woodin, 2021; Rodriguez-Moreno and Sihra, 2007; Valbuena and Lerma, 2016). Like many of these ion channels, the structure of the ASIC extracellular and transmembrane regions have been determined (Baconguis et al, 2014; Gonzales et al, 2009; Yoder and Gouaux, 2020; Yoder et al, 2018) but the intracellular domains are unresolved. Understanding the coarse outline of the two ICDs, the N and C tails, as well as their pH-induced movements, would inform further investigation of ASIC metabotropic signaling and may shed light on how the ICDs impact gating, protein-protein interactions and/or trafficking (Baron et al, 2002; Chai et al, 2007; Hruska-Hageman et al, 2004; Kellenberger and Schild, 2015; Klipp et al, 2020; Leonard et al, 2003; Schnizler et al, 2009)

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