title: The Thumb Domain Mediates Acid-sensing Ion Channel Desensitization.
abstract: Acid-sensing ion channels (ASICs) are cation-selective proton-gated channels expressed in neurons that participate in diverse physiological processes, including nociception, synaptic plasticity, learning, and memory. ASIC subunits contain intracellular N and C termini, two transmembrane domains that constitute the pore, and a large extracellular loop with defined domains termed the finger, β-ball, thumb, palm, and knuckle. Here we examined the contribution of the finger, β-ball, and thumb domains to activation and desensitization through the analysis of chimeras and the assessment of the effect of covalent modification of introduced Cys at the domain-domain interfaces. Our studies with ASIC1a-ASIC2a chimeras showed that swapping the thumb domain between subunits results in faster channel desensitization. Likewise, the covalent modification of Cys residues at selected positions in the β-ball-thumb interface accelerates the desensitization of the mutant channels. Studies of accessibility with thiol-reactive reagents revealed that the β-ball and thumb domains reside apart in the resting state but that they become closer to each other in response to extracellular acidification. We propose that the thumb domain moves upon continuous exposure to an acidic extracellular milieu, assisting with the closing of the pore during channel desensitization.
authors.affiliation: From the Renal-Electrolyte Division, Department of Medicine, and.
authors.forename: Aram J
authors.initials: AJ
authors.lastname: Krauson
authors.affiliation: From the Renal-Electrolyte Division, Department of Medicine, and Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261 mdc4@pitt.edu.
authors.forename: Marcelo D
authors.initials: MD
authors.lastname: Carattino
mesh_terms: D062565:Acid Sensing Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D000818:Animals; D055664:Electrochemical Techniques; D005260:Female; D051379:Mice; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: C568267:ASIC1 protein, mouse; C568265:ASIC2 protein, mouse; D062565:Acid Sensing Ion Channels; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins
keywords: acid sensing ion channel (ASIC); conformational change; epithelial sodium channel (ENaC); ion channel; receptor desensitization