title: Interactions of divalent cations with calcium binding sites of BK channels reveal independent motions within the gating ring.
abstract: Large-conductance voltage- and calcium-activated K+(BK) channels are key physiological players in muscle, nerve, and endocrine function by integrating intracellular Ca2+and membrane voltage signals. The open probability of BK channels is regulated by the intracellular concentration of divalent cations sensed by a large structure in the BK channel called the "gating ring," which is formed by four tandems of regulator of conductance for K+(RCK1 and RCK2) domains. In contrast to Ca2+that binds to both RCK domains, Mg2+, Cd2+, or Ba2+interact preferentially with either one or the other. Interaction of cations with their binding sites causes molecular rearrangements of the gating ring, but how these motions occur remains elusive. We have assessed the separate contributions of each RCK domain to the cation-induced gating-ring structural rearrangements, using patch-clamp fluorometry. Here we show that Mg2+and Ba2+selectively induce structural movement of the RCK2 domain, whereas Cd2+causes motions of RCK1, in all cases substantially smaller than those elicited by Ca2+By combining divalent species interacting with unique sites, we demonstrate that RCK1 and RCK2 domains move independently when their specific binding sites are occupied. Moreover, binding of chemically distinct cations to both RCK domains is additive, emulating the effect of fully occupied Ca2+binding sites.
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892; pablo.mirandafernandez2@nih.gov.
authors.forename: Pablo
authors.initials: P
authors.lastname: Miranda
authors.affiliation: Departamento de Ciencias Médicas Básicas, Instituto de Tecnologías Biomédicas y Centro de Investigaciones Biomédicas de Canarias, Universidad de La Laguna, 38071 La Laguna, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Giraldez
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Miguel
authors.initials: M
authors.lastname: Holmgren
mesh_terms: D000494:Allosteric Regulation / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000502:physiology; D002412:Cations / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000502:physiology; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000378:metabolism; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D021122:Protein Subunits; D014982:Xenopus laevis / Q000196:embryology
chemical_list: D002135:Calcium-Binding Proteins; D002412:Cations; D002413:Cations, Divalent; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D021122:Protein Subunits; D002118:Calcium
keywords: FRET; SLO1 channel; allosteric regulation; divalent ions