Characterization of an LQT5-related mutation in KCNE1, Y81C: implications for a role of KCNE1 cytoplasmic domain in IKs channel function.
BACKGROUND
Y81C is a new long QT-5 (LQT5)-related KCNE1 mutation, which is located in the post-transmembrane domain (post-TMD) region in close proximity to three other LQT5 mutations (S74L, D76N, and W87R).


OBJECTIVE
We examine the effects of Y81C on the function and drug sensitivity of the slow delayed rectifier channel (I(Ks)) formed by KCNE1 with pore-forming KCNQ1 subunits. We also infer a structural basis for the detrimental effects of Y81C on I(Ks) function.


METHODS
Wild-type (WT) and mutant (harboring Y81C) I(Ks) channels are expressed in oocytes or COS-7 cells. Channel function and KCNQ1 protein expression/subcellular distribution are studied by techniques of electrophysiology, biochemistry, and immunocytochemistry. Ab initio structure predictions of KCNE1 cytoplasmic domain are performed by the Robetta server.


RESULTS
Relative to WT KCNE1, Y81C reduces I(Ks) current amplitude and shifts the voltage range of activation to a more positive range. Y81C does not reduce whole-cell KCNQ1 protein level or interfere with KCNQ1 trafficking to cell surface. Thus, its effects are mediated by altered KCNQ1/KCNE1 interactions in cell surface channels. Importantly, Y81C potentiates the effects of an I(Ks) activator. Preserving the aromatic or hydroxyl side chain at position 81 (Y81F or Y81T) does not prevent the detrimental effects of Y81C. Structure predictions suggest that the post-TMD region of KCNE1 may adopt a helical secondary structure.


CONCLUSIONS
We propose that the post-TMD region of KCNE1 interacts with the KCNQ1 channel to modulate I(Ks) current amplitude and gating kinetics. Other LQT5 mutations in this region share the Y81C phenotype and probably affect the I(Ks) channel function by a similar mechanism.
Wu
Dong-Mei
DM
Department of Physiology, Virginia Commonwealth University, Richmond, 23298, USA.
Lai
Ling-Ping
LP
Zhang
Mei
M
Wang
Hui-Liang
HL
Jiang
Min
M
Liu
Xian-Sheng
XS
Tseng
Gea-Ny
GN
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003593:Cytoplasm; D005786:Gene Expression Regulation; D007150:Immunohistochemistry; D051656:KCNQ Potassium Channels / Q000235:genetics* / Q000378:metabolism*; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism*; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D009865:Oocytes; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics / Q000378:metabolism
D051656:KCNQ Potassium Channels; D024642:Potassium Channels, Voltage-Gated