Dynamic conformational changes of acid-sensing ion channels in different desensitizing conditions

Holm, Caroline Marcher; Topaktas, Asli B.; Dannesboe, Johs; Pless, Stephan A.; Heusser, Stephanie A.

doi:10.1016/j.bpj.2024.03.038

Cited by 1 publication

(1 citation statement)

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“…However, in the desensitized structures this linker adopts a “downward” conformation (Figure 1A), uncoupling conformational changes and thereby allowing the extracellular domain to remain in the active protonated form while the pore closes 15,16,18 . This structural proposal has been supported by multiple lines of evidence including molecular dynamics, extensive mutagenesis, state-dependent non-canonical amino acid photocrosslinking and voltage clamp fluorometry 16–19 . While other channel regions can impact the desensitization process 20–22 , accumulating evidence points to the β11-12 linker as the critical substrate for ASIC desensitization.…”

Section: Introductionmentioning

confidence: 85%

Proline substitutions in the ASIC1 β11-12 linker slow desensitization

Purohit,

Couch,

MacLean

2024

Preprint

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Desensitization is a prominent feature of nearly all ligand gated ion channels. Acid-sensing ion channels (ASIC) undergo desensitization within hundreds of milliseconds to seconds upon continual extracellular acidification. The ASIC mechanism of desensitization is primarily due to the isomerization or ″flipping″ of a short linker joining the 11th and 12th beta sheets in the extracellular domain. In the resting and active states this β11-12 linker adopts an ″upward″ conformation while in the desensitized conformation the linker assumes a″downward″ state. To accommodate this ″downward″ state, specific peptide bonds within the linker adopt either trans-like or cis-like conformations. Since proline-containing peptide bonds undergo cis-trans isomerization very slowly, we hypothesized that introducing proline residues in the linker may slow or even abolish ASIC desensitization, potentially providing a valuable research tools. Proline substitutions in the chicken ASIC1 β11-12 linker (L414P and Y416P) slowed desensitization decays approximately 100 to 1000-fold as measured in excised patches. Both L414P and Y416P shifted the steady state desensitization curves to more acidic pHs while activation curves and ion selectivity of these slow-desensitizing currents were largely unaffected. To investigate the functional stoichiometry of desensitization in the trimeric ASIC, we created families of L414P and Y416P concatemers with zero, one, two or three proline substitutions in all possible configurations. Introducing one or two L414P or Y416P mutations only slightly attenuated desensitization, suggesting that conformational changes in the remaining faster wild type subunits were sufficient to desensitize the channel. These data highlight the unusual cis-trans isomerization mechanism of ASIC desensitization and support a model where a single subunit is sufficient to desensitize the entire channel.

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