Protons activate brain Na+ channel 1 by inducing a conformational change that exposes a residue associated with neurodegeneration.
BNC1 is a mammalian neuronal cation channel in the novel DEG/ENaC ion channel family. BNC1 channels are transiently activated by extracellular protons and are constitutively activated by insertion of large residues, such as valine, in place of Gly-430; residue 430 is a site where analogous mutations in some Caenorhabditis elegans family members cause a swelling neurodegeneration. Mutation of Gly-430 to a small amino acid, cysteine, neither generated constitutive currents nor allowed modification of this residue by sulfhydryl-reactive methanethiosulfonate (MTS) compounds. However, when protons activated the channel, Cys-430 became accessible to extracellular MTS reagents, which modified Cys-430 to generate constitutive currents. Fluorescent MTS reagents also labeled Cys-430 in activated channels. These data indicate that protons induce a reversible conformational change that activates BNC1 thereby exposing residue 430 to the extracellular solution. Once Cys-430 is modified with a large chemical group, the channel is prevented from relaxing back to the inactive state. These results link ligand-dependent activation and activation by mutations that cause neurodegeneration.
Adams
C M
CM
Howard Hughes Medical Institute, Departments of Internal Medicine and Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
Snyder
P M
PM
Price
M P
MP
Welsh
M J
MJ
D019943:Amino Acid Substitution; D000818:Animals; D003080:Cold Temperature; D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D005020:Ethyl Methanesulfonate / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D007202:Indicators and Reagents / Q000494:pharmacology; D015640:Ion Channel Gating; D007473:Ion Channels; D008698:Mesylates / Q000494:pharmacology; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D019636:Neurodegenerative Diseases / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D011487:Protein Conformation / Q000187:drug effects; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D007202:Indicators and Reagents; D007473:Ion Channels; D008698:Mesylates; D009419:Nerve Tissue Proteins; D015222:Sodium Channels; C093171:methanethiosulfonate ethylammonium; C109153:(2-sulfonatoethyl)methanethiosulfonate; D005020:Ethyl Methanesulfonate