Atypical gating of M-type potassium channels conferred by mutations in uncharged residues in the S4 region of KCNQ2 causing benign familial neonatal convulsions.
Heteromeric assembly of KCNQ2 and KCNQ3 subunits underlie the M-current (I(KM)), a slowly activating and noninactivating neuronal K(+) current. Mutations in KCNQ2 and KCNQ3 genes cause benign familial neonatal convulsions (BFNCs), a rare autosomal-dominant epilepsy of the newborn. In the present study, we describe the identification of a novel KCNQ2 heterozygous mutation (c587t) in a BFNC-affected family, leading to an alanine to valine substitution at amino acid position 196 located at the N-terminal end of the voltage-sensing S(4) domain. The consequences on KCNQ2 subunit function prompted by the A196V substitution, as well as by the A196V/L197P mutation previously described in another BFNC-affected family, were investigated by macroscopic and single-channel current measurements in CHO cells transiently transfected with wild-type and mutant subunits. When compared with KCNQ2 channels, homomeric KCNQ2 A196V or A196V/L197P channels showed a 20 mV rightward shift in their activation voltage dependence, with no concomitant change in maximal open probability or single-channel conductance. Furthermore, current activation kinetics of KCNQ2 A196V channels displayed an unusual dependence on the conditioning prepulse voltage, being markedly slower when preceded by prepulses to more depolarized potentials. Heteromeric channels formed by KCNQ2 A196V and KCNQ3 subunits displayed gating changes similar to those of KCNQ2 A196V homomeric channels. Collectively, these results reveal a novel role for noncharged residues in the N-terminal end of S(4) in controlling gating of I(KM) and suggest that gating changes caused by mutations at these residues may decrease I(KM) function, thus causing neuronal hyperexcitability, ultimately leading to neonatal convulsions.
Soldovieri
Maria Virginia
MV
Section of Pharmacology, Department of Neuroscience, University of Naples Federico II, 80131 Naples, Italy.
Cilio
Maria Roberta
MR
Miceli
Francesco
F
Bellini
Giulia
G
Miraglia del Giudice
Emanuele
E
Castaldo
Pasqualina
P
Hernandez
Ciria C
CC
Shapiro
Mark S
MS
Pascotto
Antonio
A
Annunziato
Lucio
L
Taglialatela
Maurizio
M
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D016466:CHO Cells; D002675:Child, Preschool; D006224:Cricetinae; D003412:Cricetulus; D020936:Epilepsy, Benign Neonatal / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D006801:Humans; D007223:Infant; D015640:Ion Channel Gating / Q000235:genetics* / Q000502:physiology; D051658:KCNQ2 Potassium Channel / Q000235:genetics* / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D010375:Pedigree
D051658:KCNQ2 Potassium Channel