Chimeric mutations in the M2 segment of the 5-hydroxytryptamine-gated chloride channel MOD-1 define a minimal determinant of anion/cation permeability.
The ionic selectivity of ligand-gated ion channels (LGICs) determines whether receptor activation produces an excitatory or inhibitory response. The determinants of anion/cation selectivity were investigated for a new member of the LGIC superfamily, MOD-1, a serotonin-gated chloride channel cloned from the nematode Caenorhabditis elegans. In common with other anionic LGICs (glycine receptors and GABA(A) receptors), the selectivity triple mutant in the pore-forming M2 segment (proline insertion, Ala --> Glu substitution at the central ring, and Thr --> Val at the hydrophobic ring) converted the selectivity of MOD-1 from anionic to cationic. Unlike other LGICs, however, this mutant in MOD-1 was highly selective for K+ over other cations. Subsets of this selectivity triple mutant were studied to define the minimal change required for conversion from anion-permeable to cation-permeable. The double mutant at the central ring of charge (deltaPro-269/A270E) produced a non-selective cation channel. Charge reversal at the central ring alone (A270E) was sufficient to convert MOD-1 to cation-permeable. These results refine the determinants of ion-charge selectivity in LGICs and demonstrate the critical role of the central ring of charge formed by the M2 segments.
Menard
Claudine
C
Centre de Recherche de Biochemie Macromoléculaire, CNRS FRE2593, 1919 Route de Mende, 34293 Montpellier, France. menard@crbm.cnrs.fr
Horvitz
H Robert
HR
Cannon
Stephen
S
D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D000838:Anions; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics*; D002412:Cations; D018118:Chloride Channels / Q000737:chemistry / Q000235:genetics*; D017124:Conserved Sequence; D004594:Electrophysiology; D005260:Female; D018698:Glutamic Acid / Q000737:chemistry; D007477:Ions; D008024:Ligands; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010539:Permeability; D011188:Potassium / Q000737:chemistry; D011189:Potassium Chloride / Q000494:pharmacology; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D012701:Serotonin / Q000737:chemistry*; D012965:Sodium Chloride / Q000494:pharmacology; D014982:Xenopus laevis
D000838:Anions; D029742:Caenorhabditis elegans Proteins; D002412:Cations; D018118:Chloride Channels; D007477:Ions; D008024:Ligands; C417030:MOD-1 protein, C elegans; D011993:Recombinant Fusion Proteins; D012701:Serotonin; D018698:Glutamic Acid; D012965:Sodium Chloride; D011189:Potassium Chloride; D000409:Alanine; D011188:Potassium