K+ conduction and Mg2+ blockade in a Shaker Kv-channel single point mutant with an unusually high conductance

Cristian Moscoso, Ariela Vergara-Jaque, Valeria Márquez-Miranda, Romina V. Sepúlveda, Ignacio Valencia, Ignacio Díaz-Franulic, Fernando González-Nilo, David Naranjo

Resultado de la investigación: Contribución a una revistaArtículo

6 Citas (Scopus)

Resumen

Potassium channels exhibit a large diversity of single-channel conductances. Shaker is a low-conductance K-channel in which Pro475→Asp, a single-point mutation near the internal pore entrance, promotes 6- to 8-fold higher unitary current. To assess the mechanism for this higher conductance, we measured Shaker-P475D single-channel current in a wide range of symmetrical K+ concentrations and voltages. Below 300 mM K+, the current-to-voltage relations (i-V) showed inward rectification that disappeared at 1000 mM K+. Single-channel conductance reached a maximum of ∼190 pS at saturating [K+], a value 4- to 5-fold larger than that estimated for the native channel. Intracellular Mg2+ blocked this variant with ∼100-fold higher affinity. Near zero voltage, blockade was competitively antagonized by K+; however, at voltages >100 mV, it was enhanced by K+. This result is consistent with a lock-in effect in a single-file diffusion regime of Mg2+ and K+ along the pore. Molecular-dynamics simulations revealed higher K+ density in the pore, especially near the Asp-475 side chains, as in the high-conductance MthK bacterial channel. The molecular dynamics also showed that K+ ions bound distally can coexist with other K+ or Mg2+ in the cavity, supporting a lock-in mechanism. The maximal K+ transport rate and higher occupancy could be due to a decrease in the electrostatic energy profile for K+ throughout the pore, reducing the energy wells and barriers differentially by ∼0.7 and ∼2 kT, respectively.

Idioma originalInglés
Páginas (desde-hasta)1198-1207
Número de páginas10
PublicaciónBiophysical Journal
Volumen103
N.º6
DOI
EstadoPublicada - 19 sep 2012

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  • Biofísica

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