Phosphatidylinositol 4,5-bisphosphate (PIP2) regulates KCNQ3 K+ channels by interacting with four cytoplasmic channel domains

Abstract

Edited by Mike Shipston Phosphatidylinositol 4,5-bisphosphate (PIP 2) in the plasma membrane regulates the function of many ion channels, including M-type (potassium voltage-gated channel subfamily Q member (KCNQ), K v 7) K ؉ channels; however, the molecular mechanisms involved remain unclear. To this end, we here focused on the KCNQ3 subtype that has the highest apparent affinity for PIP 2 and performed extensive mutagenesis in regions suggested to be involved in PIP 2 interactions among the KCNQ family. Using perforated patch-clamp recordings of heterologously transfected tissue culture cells, total internal reflection fluorescence microscopy, and the zebrafish (Danio rerio) voltage-sensitive phosphatase to deplete PIP 2 as a probe, we found that PIP 2 regulates KCNQ3 channels through four different domains: 1) the A-B helix linker that we previously identified as important for both KCNQ2 and KCNQ3, 2) the junction between S6 and the A helix, 3) the S2-S3 linker, and 4) the S4-S5 linker. We also found that the apparent strength of PIP 2 interactions within any of these domains was not coupled to the voltage dependence of channel activation. Extensive homology modeling and docking simulations with the WT or mutant KCNQ3 channels and PIP 2 were consistent with the experimental data. Our results indicate that PIP 2 modulates KCNQ3 channel function by interacting synergistically with a minimum of four cytoplasmic domains. Voltage-gated K ϩ (K v) 4 channels play critical roles in the function of various tissues, including brain, heart, and epithelia (1). Among K v channels, KCNQ1-5 (K v 7.1-7.5) channels are regulated by several intracellular signaling molecules, including phosphatidylinositol 4,5-bisphosphate (PIP 2), which is present in the inner leaflet of the cell plasma membrane at only modest abundance. For some time, it has been known that interactions with PIP 2 regulate M-channel activity (2-7). However, the answers to several key questions remain elusive: How and where does PIP 2 regulate KCNQ channels, and are those mechanisms disparate between KCNQ1-containing channels and the others, or do they generalize among KCNQ1-5? To understand the molecular mechanisms by which PIP 2 regulates KCNQ channels, it is necessary to identify the site(s) of PIP 2 interaction. K v channels are tetramers of subunits containing six transmembrane domains (S1-S6). The earliest study suggested that PIP 2 interacts with the junction between S6 and the first C-terminal "A helix" (which we call the S6Jx domain) of KCNQ2; thus, replacement of the histidine at position 328 in the S6Jx of KCNQ2 (His 367 in KCNQ3; Fig. 1A) by a cysteine reduced the sensitivity of the channel to PIP 2 (4). We identified a "cationic cluster" (Lys 452 , Arg 459 , and Arg 461 in KCNQ2) in the linker between the A and B helices (A-B linker) of KCNQ2 and KCNQ3, which were suggested to form electrostatic bonds with the phosphate headgroups of PIP 2 molecules (8). Expanding on those findings, Tinker and co-workers (9) localized a cluster of basic residues (L...

Calmodulin acts as a state-dependent switch to control a cardiac potassium channel opening

“…PIP2 plays a vital role in our model by interaction with the S2-S3 linker to facilitate channel transition into the AO state. This is consistent with previous studies suggesting that PIP2 binds the S2-S3 linker (15,36,(47)(48)(49). However, the S2-S3 linker may not be the only PIP2 binding site.…”

“…These regions have also been suggested to bind PIP2 in other KCNQ channels (49). The S4-S5 linker, S5, and S6 may form a second PIP2 binding site specifically important for VSD-pore coupling in both the IO and AO states.…”

A mutually induced conformational fit underlies Ca2+-directed interactions between calmodulin and the proximal C terminus of KCNQ4 K+ channels

“…It also is in accord with the need for CaM for functional expression (28,39,58). However, we do not believe that CaM interacts with the voltage-sensor domain of KCNQ2-5 channels and that as for PIP 2 actions on those channels (94), effects on voltage dependence are minimal. Future studies to test the affinities of the peptides with inactive N-or C-lobe CaM mutants and these domains will further probe whether this lobe-switching mechanism is indeed correct.…”

Identifying mutation hotspots reveals pathogenetic mechanisms of KCNQ2 epileptic encephalopathy

“…To test if selected EE mutations alter PIP 2 affinity, we examined the K v 7.2 current decay upon PIP 2 depletion induced by activation of voltage-sensitive phosphatase (VSP) 11,42,44 . In CHOhm1 cells coexpressing danio rerio VSP 11 , the 10s-depolarization step at voltages from +40 mV decreased peak currents of K v 7.2 channels, reaching the maximal decay of 53.2 ± 4.0% at +100 mV ( Supplementary Fig.…”