Selective exclusion and selective binding both contribute to ion selectivity in KcsA, a model potassium channel

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Título: Selective exclusion and selective binding both contribute to ion selectivity in KcsA, a model potassium channel
Autor/es: Renart, M. Lourdes | Montoya, Estefanía | Giudici, A. Marcela | Poveda, José A. | Fernández, Asia M. | Morales, Andrés | González-Ros, José M.
Grupo/s de investigación o GITE: Fisiología de Membranas
Centro, Departamento o Servicio: Universidad de Alicante. Departamento de Fisiología, Genética y Microbiología
Palabras clave: Potassium channels | Selective exclusion | Selective binding | Ion selectivity | KcsA
Área/s de conocimiento: Fisiología
Fecha de publicación: 15-sep-2017
Editor: American Society for Biochemistry and Molecular Biology
Cita bibliográfica: The Journal of Biological Chemistry. 2017, 292(37): 15552-15560. doi:10.1074/jbc.M117.795807
Resumen: The selectivity filter in potassium channels, a main component of the ion permeation pathway, configures a stack of binding sites (sites S1–S4) to which K+ and other cations may bind. Specific ion binding to such sites induces changes in the filter conformation, which play a key role in defining both selectivity and permeation. Here, using the potassium channel KcsA as a model, we contribute new evidence to reinforce this assertion. First, ion binding to KcsA blocked by tetrabutylammonium at the most cytoplasmic site in the selectivity filter (S4) suggests that such a site, when in the nonconductive filter conformation, has a higher affinity for cation binding than the most extracellular S1 site. This filter asymmetry, along with differences in intracellular and extracellular concentrations of K+ versus Na+ under physiological conditions, should strengthen selection of the permeant K+ by the channel. Second, we used different K+ concentrations to shift the equilibrium between nonconductive and conductive states of the selectivity filter in which to test competitive binding of Na+. These experiments disclosed a marked decrease in the affinity of Na+ to bind the channel when the conformational equilibrium shifts toward the conductive state. This finding suggested that in addition to the selective binding of K+ and other permeant species over Na+, there is a selective exclusion of nonpermeant species from binding the channel filter, once it reaches a fully conductive conformation. We conclude that selective binding and selective exclusion of permeant and nonpermeant cations, respectively, are important determinants of ion channel selectivity.
Patrocinador/es: This work was funded in part by Grants BFU2012-31359 and BFU2015-66612-P from the Spanish MINECO/FEDER.
URI: http://hdl.handle.net/10045/69337
ISSN: 0021-9258 (Print) | 1083-351X (Online)
DOI: 10.1074/jbc.M117.795807
Idioma: eng
Tipo: info:eu-repo/semantics/article
Derechos: © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
Revisión científica: si
Versión del editor: http://dx.doi.org/10.1074/jbc.M117.795807
Aparece en las colecciones:INV - Fisiología de Membranas - Artículos de Revistas

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