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...

Background:Little is known about the structural characteristics of the multimodal TRPV1 ion channel. Results: FRET measurements show the C terminus surrounded by the N terminus arranged with 4-fold symmetry. The N terminus is further away from the plasma membrane than the C terminus. Conclusion: Domain organization is consistent with a compact structure of the channel. Significance: This work presents novel insights regarding the structure of TRPV1.

The pH-sensitive fluorescent protein Venus can be used as an optical reporter for proton flux when fused to an intracellular domain of Hv1 channels.

Hv1 proteins form a voltage-gated proton channel that is inhibited by extracellular Zn2+. De La Rosa et al find that extracellular Zn2+ is octahedrally coordinated by specific protein atoms and that Zn2+ occupancy modulates voltage sensor activation in Hv1 by long-range conformational coupling to a conserved intracellular electrostatic network.

The Hv1 proton channel shares striking structural homology with fourth transmembrane helical segment-type voltage-sensor (VS) domains but manifests distinctive functional properties, including a proton-selective "aqueous" conductance and allosteric control of voltage-dependent gating by changes in the transmembrane pH gradient. The mechanisms responsible for Hv1's functional properties remain poorly understood, in part because methods for measuring gating currents that directly report VS activation have not yet been described. Here, we describe an approach that allows robust and reproducible measurement of gating-associated charge movements in Hv1. Gating currents reveal that VS activation and proton-selective aqueous conductance opening are thermodynamically distinct steps in the Hv1 activation pathway and show that pH changes directly alter VS activation. The availability of an assay for gating currents in Hv1 may aid future efforts to elucidate the molecular mechanisms of gating cooperativity, pH-dependent modulation, and H selectivity in a model VS domain protein.