Conformational dynamics and role of the acidic pocket in ASIC pH-dependent gating.
Acid-sensing ion channels (ASICs) are proton-activated Na+channels expressed in the nervous system, where they are involved in learning, fear behaviors, neurodegeneration, and pain sensation. In this work, we study the role in pH sensing of two regions of the ectodomain enriched in acidic residues: the acidic pocket, which faces the outside of the protein and is the binding site of several animal toxins, and the palm, a central channel domain. Using voltage clamp fluorometry, we find that the acidic pocket undergoes conformational changes during both activation and desensitization. Concurrently, we find that, although proton sensing in the acidic pocket is not required for channel function, it does contribute to both activation and desensitization. Furthermore, protonation-mimicking mutations of acidic residues in the palm induce a dramatic acceleration of desensitization followed by the appearance of a sustained current. In summary, this work describes the roles of potential pH sensors in two extracellular domains, and it proposes a model of acidification-induced conformational changes occurring in the acidic pocket of ASIC1a.
Department of Pharmacology and Toxicology, Faculty of Biology and Medicine, University of Lausanne, 1011 Lausanne, Switzerland.
Sabrina
S
Vullo
Department of Pharmacology and Toxicology, Faculty of Biology and Medicine, University of Lausanne, 1011 Lausanne, Switzerland.
Gaetano
G
Bonifacio
Department of Pharmacology and Toxicology, Faculty of Biology and Medicine, University of Lausanne, 1011 Lausanne, Switzerland.
Sophie
S
Roy
SIB (Swiss Institute of Bioinformatics), Biozentrum, University of Basel, 4056 Basel, Switzerland.|Biozentrum, University of Basel, 4056 Basel, Switzerland.
Niklaus
N
Johner
SIB (Swiss Institute of Bioinformatics), Biozentrum, University of Basel, 4056 Basel, Switzerland.|Biozentrum, University of Basel, 4056 Basel, Switzerland.
Simon
0000-0002-6274-4094
S
Bernèche
Department of Pharmacology and Toxicology, Faculty of Biology and Medicine, University of Lausanne, 1011 Lausanne, Switzerland; stephan.kellenberger@unil.ch.
Stephan
0000-0003-1755-6198
S
Kellenberger
D062565:Acid Sensing Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D009154:Mutation; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000378:metabolism*; D014118:Toxins, Biological / Q000378:metabolism*
C568266:ASIC1 protein, human; D062565:Acid Sensing Ion Channels; D014118:Toxins, Biological; D012964:Sodium
acid-sensing ion channel; conformational changes; kinetic model; pH sensing; voltage clamp fluorometry