Mutations causing neurodegeneration in Caenorhabditis elegans drastically alter the pH sensitivity and inactivation of the mammalian H+-gated Na+ channel MDEG1.
The mammalian degenerin MDEG1 belongs to the nematode degenerin/epithelial Na+ channel superfamily. It is constitutively activated by the same mutations that cause gain-of-function of the Caenorhabditis elegans degenerins and neurodegeneration. ASIC and DRASIC, which were recently cloned, are structural homologues of MDEG1 and behave as H+-gated cation channels. MDEG1 is also a H+-activated Na+ channel, but it differs from ASIC in its lower pH sensitivity and slower kinetics. In addition to the generation of a constitutive current, mutations in MDEG1 also alter the properties of the H+-gated current. Replacement of Gly-430 in MDEG1 by bulkier amino acids, such as Val, Phe, or Thr, drastically increases the H+ sensitivity of the channel (half-maximal pH (pHm) approximately 4.4 for MDEG1, pHm approximately 6.7 for the different mutants). Furthermore, these replacements completely suppress the inactivation observed with the wild-type channel and increase the sensitivity of the H+-gated channel to blockade by amiloride by a factor of 10 without modification of its conductance and ionic selectivity. These results as well as those obtained with other mutants clearly indicate that the region surrounding Gly-430, situated just before the second transmembrane segment, is essential for pH sensitivity and gating.
Champigny
G
G
Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UPR 411, Sophia Antipolis, 06560 Valbonne, France.
Voilley
N
N
Waldmann
R
R
Lazdunski
M
M
D019943:Amino Acid Substitution; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000378:metabolism; D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism; D014981:Xenopus
D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D015222:Sodium Channels