title: A pore-lining glutamic acid in the rat olfactory cyclic nucleotide-gated channel controls external spermine block.
abstract: Spermine is a potent, voltage-dependent blocker of the olfactory cyclic nucleotide-gated channel from both the intracellular and extracellular sides. However, its sites of action are unknown. This study investigated the external spermine binding site in the rat CNCalpha3 subunit. Neutralization of a glutamic acid residue (E342Q) in the P-loop region eliminated voltage-dependence of block by externally applied spermine. The charge-conservative E342D mutation had little effect on spermine block. Thus, E342 forms the binding site for externally applied spermine. However, spermine remained a potent voltage-independent blocker of the E342Q mutant channel, suggesting that the mutation either created a novel binding site outside the membrane electrical field or that it dramatically changed the properties of the existing pore site.
authors: Department of Physiology and Pharmacology, University of Queensland, QLD 4072, Brisbane, Australia.
authors: S T
authors: ST
authors: Nevin
authors: J L
authors: JL
authors: Haddrill
authors: J W
authors: JW
authors: Lynch
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007473:Ion Channels / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009154:Mutation / Q000187:drug effects / Q000502:physiology; D018034:Olfactory Receptor Neurons / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D017434:Protein Structure, Tertiary / Q000187:drug effects / Q000235:genetics; D051381:Rats; D013096:Spermine / Q000494:pharmacology*
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D013096:Spermine; D018698:Glutamic Acid; D000242:Cyclic AMP