A single ring of charged amino acids at one end of the pore can control ion selectivity in the 5-HT3 receptor.
1. To determine the mechanisms by which cation- or anion-specific channels select between these ions, we have examined the role of electrostatic factors in a typical ligand-gated ion channel, the 5-hydroxytryptamine3 (5-HT3) receptor, by removal and/or insertion of rings of conserved charged residues at either end of the pore. 2. Neutralization of the negatively charged ring at the intracellular end of the channel (E-1'A) results in a nonselective channel (PNa/PCl=0.89). 3. Insertion of positively charged residues at the extracellular end of the pore either results in a nonfunctional receptor (A24'K) or one that remains cation-selective (PNa/PCl=110; S19'R). 4. Combining the removal of a negatively charged ring (E-1'A) with the insertion of a positively charged ring (S19'R), however, results in a channel that is predominantly anion-selective (PNa/PCl=0.37). 5. The data suggest that for the cation-selective 5-HT3 receptor, the control of selectivity exerted by charged rings at either end of the pore is dominated by the ring of negatively charged residues at the intracellular side of the channel. As changing the charge at this position has also been shown to change ionic selectivity in anion-selective receptors, these data suggest that electrostatic factors can control selectivity in the whole Cys-loop family.
Thompson
Andrew J
AJ
Department of Biochemistry, University of Cambridge, Cambridge CB2 IGA, UK.
Lummis
Sarah C R
SC
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000596:Amino Acids / Q000737:chemistry / Q000235:genetics*; D000838:Anions / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics* / Q000502:physiology; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D007477:Ions / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D044406:Receptors, Serotonin, 5-HT3 / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012701:Serotonin / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D014162:Transfection
D000596:Amino Acids; D000838:Anions; D007473:Ion Channels; D007477:Ions; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin; D012965:Sodium Chloride; D002118:Calcium