title: Independent contribution of extracellular proton binding sites to ASIC1a activation.
abstract: Acid-sensing ion channels (ASICs) are a group of trimeric cation permeable channels gated by extracellular protons that are mainly expressed in the nervous system. Despite the structural information available for ASIC1, there is limited understanding of the molecular mechanism that allows these channels to sense and respond to drops in extracellular pH. In this report, we employed the substituted cysteine accessibility method and site-directed mutagenesis to examine the mechanism of activation of ASIC1a by extracellular protons. We found that the modification of E238C and D345C channels by MTSET reduced proton apparent affinity for activation. Furthermore, the introduction of positively charged residues at position 345 rendered shifted biphasic proton activation curves. Likewise, channels bearing mutations at positions 79 and 416 in the palm domain of the channel showed reduced proton apparent affinity and biphasic proton activation curves. Of significance, the effect of the mutations at positions 79 and 345 on channel activation was additive. E79K-D345K required a change to a pH lower than 2 for maximal activation. In summary, this study provides direct evidence for the presence of two distinct proton coordination sites in the extracellular region of ASIC1a, which jointly facilitate pore opening in response to extracellular acidification.
authors.affiliation: From the Division of Renal Electrolytes, Department of Medicine, and.
authors.forename: Aram J
authors.initials: AJ
authors.lastname: Krauson
authors.forename: Anna C
authors.initials: AC
authors.lastname: Rued
authors.forename: Marcelo D
authors.initials: MD
authors.lastname: Carattino
mesh_terms: D062565:Acid Sensing Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009420:Nervous System / Q000378:metabolism*; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011522:Protons; D013329:Structure-Activity Relationship; D015533:Transcriptional Activation / Q000235:genetics; D014982:Xenopus laevis
chemical_list: C568267:ASIC1 protein, mouse; D062565:Acid Sensing Ion Channels; D000596:Amino Acids; D021122:Protein Subunits; D011522:Protons; D003545:Cysteine
keywords: Acid Sensing Ion Channels (ASIC); Enac; Gating; Ion Channels; Site-directed Mutagenesis