title: The interface between extracellular and transmembrane domains of homomeric Cys-loop receptors governs open-channel lifetime and rate of desensitization.
abstract: The lifetimes of activated postsynaptic receptor channels contribute to the efficiency of synaptic transmission. Here we show that structural differences within the interface dividing extracellular and transmembrane domains of homomeric alpha7 and 5-HT(3A) receptors account for the large differences in open-channel lifetime and time of desensitization onset between these contrasting members of the Cys-loop receptor superfamily. For alpha7 receptors, agonist-evoked single-channel currents appear mainly as isolated brief openings (tau(o) = 0.35 ms), whereas macroscopic currents after a step pulse of agonist desensitize rapidly (tau(d) = 0.4 ms). In contrast for 5-HT(3A) receptors, agonist-evoked single-channel currents appear as clusters of many long openings in quick succession (tau(cluster) = 1.2 s), whereas macroscopic currents desensitize slowly (tau(d) = 1.1 s). A chimeric alpha7-5HT(3A) receptor exhibits functional properties intermediate between those of the parent receptors, but the functional signatures of each parent are reconstituted after substituting the major loops within the interface of the extracellular and transmembrane domains from the corresponding parent receptor. Furthermore, these structural loops contribute to open-channel lifetime and time of desensitization onset in a nonadditive manner. The results suggest that desensitization is the major determinant of the lifetimes of activated alpha7 and 5-HT(3A) receptors and that functional differences between the two receptors arise primarily through structural differences at the interface between extracellular and transmembrane domains.
authors.affiliation: Instituto de Investigaciones Bioquímicas, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas, Bahía Blanca 8000, Argentina. inbouzat@criba.edu.ar
authors.forename: Cecilia
authors.initials: C
authors.lastname: Bouzat
authors.forename: Mariana
authors.initials: M
authors.lastname: Bartos
authors.forename: Jeremías
authors.initials: J
authors.lastname: Corradi
authors.forename: Steven M
authors.initials: SM
authors.lastname: Sine
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D005110:Extracellular Space / Q000235:genetics / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D018733:Nicotinic Antagonists / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D044406:Receptors, Serotonin, 5-HT3 / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D058831:Serotonin 5-HT3 Receptor Antagonists; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C579167:Chrna7 protein, human; C579166:Chrna7 protein, mouse; D008565:Membrane Proteins; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D044406:Receptors, Serotonin, 5-HT3; D058831:Serotonin 5-HT3 Receptor Antagonists; D064569:alpha7 Nicotinic Acetylcholine Receptor; D003545:Cysteine