title: Syntaxin-1A binds to and modulates the Slo calcium-activated potassium channel via an interaction that excludes syntaxin binding to calcium channels.
abstract: From its position in presynaptic nerve terminals, the large conductance Ca(2+)-activated K+ channel, Slo, regulates neurotransmitter release. Several other ion channels known to control neurotransmitter release have been implicated in physical interactions with the neurotransmitter release machinery. For example, the Ca(v)2.2 (N-type) Ca2+ channel binds to and is modulated by syntaxin-1A and SNAP-25. Furthermore, a close juxtaposition of Slo and Ca(v)2.2 is presumed to be necessary for functional coupling between the two channels, which has been shown in neurons. We report that Slo exhibits a strong association with syntaxin-1A. Robust co-immunoprecipitation of Slo and syntaxin-1A occurs from transfected HEK293 cells as well as from brain. However, despite this strong interaction and the known association between syntaxin-1A and the II-III loop of Ca(v)2.2, these three proteins do not co-immunoprecipitate in a trimeric complex from transfected HEK293 cells. The Slo-syntaxin-1A co-immunoprecipitation is not significantly influenced by [Ca2+]. Multiple relatively weak interactions may sum up to a tight physical coupling of full-length Slo with syntaxin-1A: the C-terminal tail and the S0-S1 loop of Slo each co-immunoprecipitate with syntaxin-1A. The presence of syntaxin-1A leads to reduced Slo channel activity due to an increased V(1/2) for activation in 100 nM, 1 muM, and 10 microM Ca2+, reduced voltage-sensitivity in 1 microM Ca2+, and slower rates of activation in 10 microM Ca2+. Potential physiological consequences of the interaction between Slo and syntaxin-1A include enhanced excitability through modulation of Slo channel activity and reduced neurotransmitter release due to disruption of syntaxin-1A binding to the Ca(v)2.2 II-III loop.
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania. scibulsky@enders.tch.harvard.edu
authors.forename: Susan M
authors.initials: SM
authors.lastname: Cibulsky
authors.forename: Hong
authors.initials: H
authors.lastname: Fei
authors.forename: Irwin B
authors.initials: IB
authors.lastname: Levitan
mesh_terms: D000954:Antigens, Surface / Q000378:metabolism*; D015153:Blotting, Western / Q000379:methods; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D051036:Large-Conductance Calcium-Activated Potassium Channels; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D018408:Patch-Clamp Techniques / Q000379:methods; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000502:physiology; D050765:Qa-SNARE Proteins; D050827:Syntaxin 1; D014162:Transfection / Q000379:methods
chemical_list: D000954:Antigens, Surface; D015220:Calcium Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D024681:Potassium Channels, Calcium-Activated; D050765:Qa-SNARE Proteins; C494212:STX1A protein, human; D050827:Syntaxin 1; D002118:Calcium