Gating consequences of charge neutralization of arginine residues in the S4 segment of K(v)7.2, an epilepsy-linked K+ channel subunit.
The K(v)7.2 subunits are the main molecular determinants of the M-current, a widespread K(+) current regulating neuronal excitability. Mutations in the K(v)7.2 gene cause benign familial neonatal seizures, an autosomally inherited human epilepsy. The benign familial neonatal seizure-causing mutations include those at arginine residues at positions 207 and 214 in the S(4) segment of K(v)7.2. In this study, each of the six S(4) arginines was individually replaced with neutral glutamines, and the functional properties of mutant channels were studied by whole-cell and single-channel voltage-clamp measurements. The results obtained suggest that each S(4) arginine residue plays a relevant role in the voltage-dependent gating of K(v)7.2 channels. In particular, a decreased positive charge at the N-terminal end of S(4) stabilized the activated state of the voltage-sensor, whereas positive-charge neutralization at the C-terminal end of S(4) favored the resting conformation. Strikingly, neutralization of a single arginine at position 201 was sufficient to cause a significant loss of voltage dependence in channel activation. Moreover, by comparing the functional properties of glutamine versus tryptophan substitution, we found steric bulk to play a relevant role at position 207, but not at position 214, in which the main functional effect of this disease-causing mutation seems to be a consequence of the loss of the positive charge.
Section of Pharmacology, Department of Neuroscience, University of Naples Federico II, Naples 80131, Italy.
Francesco
F
Miceli
Maria Virginia
MV
Soldovieri
Ciria C
CC
Hernandez
Mark S
MS
Shapiro
Lucio
L
Annunziato
Maurizio
M
Taglialatela
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001120:Arginine / Q000235:genetics; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004594:Electrophysiology; D020936:Epilepsy, Benign Neonatal / Q000235:genetics / Q000503:physiopathology*; D005973:Glutamine / Q000235:genetics; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D051658:KCNQ2 Potassium Channel / Q000235:genetics / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D018408:Patch-Clamp Techniques; D014364:Tryptophan / Q000235:genetics
D051658:KCNQ2 Potassium Channel; D005973:Glutamine; D014364:Tryptophan; D001120:Arginine