Topography and motion of acid-sensing ion channel intracellular domains

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 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 tail 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 towards 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.

Molecular Investigation of Chicken Acid-Sensing Ion Channel 1 β11-12 Linker Isomerization and Channel Kinetics

“…Thus, it is possible that the conservation of the β11-12 linker, and alterations of the surrounding areas, arose because of the physiological role of SSD rather than the precise timing of ASIC desensitization and recovery kinetics. It is also possible that the kinetics of channel desensitization and recovery are important, however, mainly in the context of slow changes in extracellular pH as have been recently examined ( Alijevic et al, 2020 ) or intracellular conformational changes which might be involved in signaling cascades ( Wang et al, 2015 , 2020 ; Couch et al, 2021 ). Understanding these issues will require a clearer accounting of the spatial-temporal dynamics of pH change in situ as well as introduction of ASICs with biophysically impactful mutations to appreciate the consequences.…”

Mambalgin-2 Inhibits Lung Adenocarcinoma Growth and Migration by Selective Interaction With ASIC1/α-ENaC/γ-ENaC Heterotrimer

“…Possibly, mambalgin-2 can bind to the ASIC1a channels in the closed or desensitized states (26,38) and activate the metabotropic signaling through the channel without the pore opening. In line with this suggestion, it was shown that the intracellular domain of the ASIC channels can interact with different intracellular signaling messengers (39).…”

Dynamic landscape of the intracellular termini of acid-sensing ion channel 1a

“…They found a slow pH dependent decrease in that ratio (Wang et al, 2020). The second study repeated this measurement with FPs that are not sensitive to pH in the pH 6-8 range and found that there was no change in the ratio of acceptor/donor fluorescence with prolonged acidification (Couch et al, 2021). YFP has a pKa of around 6.9 and its fluorescence changes dramatically between pH 7.4 and 6 (Llopis et al, 1998).…”

“…We do not think this is likely the case. First, previous work looking at the interaction between the Nzand C-termini used the same bulky FPs (Couch et al, 2021; Wang et al, 2020). In those experiments there was often an FP on each terminus.…”