A conserved ring of charge in mammalian Na+ channels: a molecular regulator of the outer pore conformation during slow inactivation.
The molecular mechanisms underlying slow inactivation in sodium channels are elusive. Our results suggest that EEDD, a highly conserved ring of charge in the external vestibule of mammalian voltage-gated sodium channels, undermines slow inactivation. By employing site-directed mutagenesis, we found that charge alterations in this asymmetric yet strong local electrostatic field of the EEDD ring significantly altered the kinetics of slow inactivation gating. Using a non-linear Poisson-Boltzmann equation, quantitative computations of the electrostatic field in a sodium channel structural model suggested a significant electrostatic repulsion between residues E403 and E758 at close proximity. Interestingly, when this electrostatic interaction was eliminated by the double mutation E403C + E758C, the kinetics of recovery from slow inactivation of the double-mutant channel was retarded by 2500% compared to control. These data suggest that the EEDD ring, located within the asymmetric electric field, is a molecular motif that critically modulates slow inactivation in sodium channels.
Xiong
Wei
W
Department of Medicine, Johns Hopkins University School of Medicine, 720 Rutland Ave/Ross 844, Baltimore, MD 21205, USA.
Farukhi
Yousaf Z
YZ
Tian
Yanli
Y
Disilvestre
Deborah
D
Li
Ronald A
RA
Tomaselli
Gordon F
GF
D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D005260:Female; D015640:Ion Channel Gating / Q000502:physiology*; D008433:Mathematics; D008564:Membrane Potentials / Q000502:physiology*; D009154:Mutation; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D018272:Porins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011487:Protein Conformation; D015222:Sodium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis
D018272:Porins; D015222:Sodium Channels