title: Extracellular Subunit Interactions Control Transitions between Functional States of Acid-sensing Ion Channel 1a.
abstract: Acid-sensing ion channels (ASICs) are neuronal, voltage-independent Na(+) channels that are transiently activated by extracellular acidification. They are involved in pain sensation, the expression of fear, and in neurodegeneration after ischemic stroke. Our study investigates the role of extracellular subunit interactions in ASIC1a function. We identified two regions involved in critical intersubunit interactions. First, formation of an engineered disulfide bond between the palm and thumb domains leads to partial channel closure. Second, linking Glu-235 of a finger loop to either one of two different residues of the knuckle of a neighboring subunit opens the channel at physiological pH or disrupts its activity. This suggests that one finger-knuckle disulfide bond (E235C/K393C) sets the channel in an open state, whereas the other (E235C/Y389C) switches the channel to a non-conducting state. Voltage-clamp fluorometry experiments indicate that both the finger loop and the knuckle move away from the β-ball residue Trp-233 during acidification and subsequent desensitization. Together, these observations reveal that ASIC1a opening is accompanied by a distance increase between adjacent thumb and palm domains as well as a movement of Glu-235 relative to the knuckle helix. Our study identifies subunit interactions in the extracellular loop and shows that dynamic changes of these interactions are critical for normal ASIC function.
authors.affiliation: Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland.
authors.forename: Karolina
authors.initials: K
authors.lastname: Gwiazda
authors.affiliation: Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland.
authors.forename: Gaetano
authors.initials: G
authors.lastname: Bonifacio
authors.affiliation: Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Vullo
authors.affiliation: Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland. Electronic address: Stephan.Kellenberger@unil.ch.
authors.forename: Stephan
authors.initials: S
authors.lastname: Kellenberger
mesh_terms: D062565:Acid Sensing Ion Channels / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D014981:Xenopus
chemical_list: C568266:ASIC1 protein, human; D062565:Acid Sensing Ion Channels; D021122:Protein Subunits
keywords: acid-sensing ion channel; disulfide; disulfide bond; electrophysiology; gating; hydrogen bond; protein-protein interaction; subunit interaction; voltage-clamp fluorometry