Stoichiometry of Kir channels with phosphatidylinositol bisphosphate

Jin, Taihao; Sui, Jin; Rosenhouse‐Dantsker, Avia; Chan, Kim W.; Jan, Yuh Nung; Logothetis, Diomedes E.

doi:10.4161/chan.2.1.5942

Cited by 12 publications

(16 citation statements)

References 49 publications

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“…Identifiable contributions of ligand binding to individual subunits to overall activity have been noted in some other ligand-gated multisubunit channels. Thus, Harpsøe et al (2011) have recently described a biphasic ligand activation curve for ( α4 ) 3 ( β2 ) 2 nicotinic acetylcholine receptor channels (very like the present data) that results from binding to distinct high- and low-affinity sites; and, individual subunit contributions to homomeric Kir potassium channel open probability as a result of PI(4,5)P 2 binding to each of the four subunits have previously been deduced from the use of mutant subunits (Jin et al, 2008). Contributions to channel gating by ligand binding to less than the maximal number of subunits, resulting in partial channel openings to subconductance levels, have also been shown for AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolpropionate)-type homotetrameric glutamate receptors (Rosenmund et al, 1998) and heterotetrameric cyclic nucleotide–gated cation channels (Ruiz and Karpen, 1997).…”

Section: Discussionsupporting

confidence: 61%

Distinct subunit contributions to the activation of M-type potassium channels by PI(4,5)P2

Telezhkin

Gibb

2012

Journal of General Physiology

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Low-threshold voltage-gated M-type potassium channels (M channels) are tetraheteromers, commonly of two Kv7.2 and two Kv7.3 subunits. Though gated by voltage, the channels have an absolute requirement for binding of the membrane phospholipid phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) to open. We have investigated the quantitative relation between the concentration of a water-soluble PI(4,5)P2 analog, dioctanoyl-PI(4,5)P2 (DiC8-PI(4,5)P2), and channel open probability (Popen) by fast application of increasing concentrations of DiC8-PI(4,5)P2 to the inside face of membrane patches excised from Chinese hamster ovary cells expressing M channels as heteromeric Kv7.2/7.3 subunits. The rationale for the experiments is that this will mimic the effect of changes in membrane PI(4,5)P2 concentration. Single-channel conductances from channel current–voltage relations in cell-attached mode were 9.2 ± 0.1 pS with a 2.5-mM pipette [K+]. Plots of Popen against DiC8-PI(4,5)P2 concentration were best fitted using a two-component concentration–Popen relationship with high and low affinity, half-maximal effective concentration (EC50) values of 1.3 ± 0.14 and 75.5 ± 2.5 µM, respectively, and Hill slopes of 1.4 ± 0.06. In contrast, homomeric channels from cells expressing only Kv7.2 or Kv7.3 constructs yielded single-component curves with EC50 values of 76.2 ± 19.9 or 3.6 ± 1.0 µM, respectively. When wild-type (WT) Kv7.2 was coexpressed with a mutated Kv7.3 subunit with >100-fold reduced sensitivity to PI(4,5)P2, the high-affinity component of the activation curve was lost. Fitting the data for WT and mutant channels to an activation mechanism with independent PI(4,5)P2 binding to two Kv7.2 and two Kv7.3 subunits suggests that the two components of the M-channel activation curve correspond to the interaction of PI(4,5)P2 with the Kv7.3 and Kv7.2 subunits, respectively, that channels can open when only the two Kv7.3 subunits have bound DiC8-PI(4,5)P2, and that maximum channel opening requires binding to all four subunits.

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Section: Discussionsupporting

confidence: 61%

Distinct subunit contributions to the activation of M-type potassium channels by PI(4,5)P2

Telezhkin

Gibb

2012

Journal of General Physiology

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“…Kir channels stand out among channel subfamilies in that they have been studied extensively in terms of both their dependence on PIPs (Table 1) and their high-resolution structures (Table 2). Several studies on Kir channels have demonstrated direct effects of PIPs on single-channel gating (43, 54, 59, 60), strongly suggesting that channel-PIP interactions affect activity by altering protein conformation and gating. An alternative or parallel mechanism by which PIPs may alter activity is through regulating the number of channels by triggering their internalization from or insertion into the plasma membrane (see below).…”

Section: Phosphoinositide Control Of the Activity Of Ion Transport Prmentioning

confidence: 99%

Phosphoinositide Control of Membrane Protein Function: A Frontier Led by Studies on Ion Channels

Logothetis

Petrou

Zhang

et al. 2015

Annu. Rev. Physiol.

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Anionic phospholipids are critical constituents of the inner leaflet of the plasma membrane, ensuring appropriate membrane topology of transmembrane proteins. Additionally, in eukaryotes, the negatively charged phosphoinositides serve as key signals not only through their hydrolysis products but also through direct control of transmembrane protein function. Direct phosphoinositide control of the activity of ion channels and transporters has been the most convincing case of the critical importance of phospholipid-protein interactions in the functional control of membrane proteins. Furthermore, second messengers, such as [Ca2+]i, or posttranslational modifications, such as phosphorylation, can directly or allosterically fine-tune phospholipid-protein interactions and modulate activity. Recent advances in structure determination of membrane proteins have allowed investigators to obtain complexes of ion channels with phosphoinositides and to use computational and experimental approaches to probe the dynamic mechanisms by which lipid-protein interactions control active and inactive protein states.

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“…Phosphorylation of Kir1.1 channels by PKA decreases the sensitivity to inhibition by PIP 2 antibodies, indicating an apparent increase in affinity for PIP 2 (Liou et al, 1999). Gβγ subunits of G-proteins and intracellular Na + alter PIP 2 sensitivity in Kir3.x channels (Huang et al, 1998; Zhang et al, 1999; Jin et al, 2008; Inanobe et al, 2010), while intracellular ATP decreases the apparent affinity of Kir6 channels for PIP 2 by reducing the channel's open probability (Baukrowitz et al, 1998; Shyng and Nichols, 1998; Enkvetchakul et al, 2000; Shyng et al, 2000; Wang et al, 2002b). …”

Section: Pip Regulation Of Kir Channelsmentioning

confidence: 99%

“…For most Kir channels, 1 or 2 open times and 1 or 2 closed times can readily be observed in single channel recordings depending on the specific isoform and recording conditions. With few exceptions (Fan and Makielski, 1997; Rohacs et al, 1999; Lopes et al, 2002), PIP 2 has generally been found to affect one or more of the closed times with no change in the open time(s) (Enkvetchakul et al, 2000; Jin et al, 2008; Xie et al, 2008; D'Avanzo et al, 2010a) suggesting a critical role for this lipid ligand in priming the channels for opening upon binding to a closed conformation. Several atomic resolution structures solved by x-ray crystallography (Nishida et al, 2007; Tao et al, 2009; Hansen et al, 2011; Whorton and MacKinnon, 2011, 2013) provide further support for this gating model.…”

Section: Pip Regulation Of Kir Channelsmentioning

confidence: 99%

Phosphoinositide regulation of inward rectifier potassium (Kir) channels

2014

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Inward rectifier potassium (Kir) channels are integral membrane proteins charged with a key role in establishing the resting membrane potential of excitable cells through selective control of the permeation of K+ ions across cell membranes. In conjunction with secondary anionic phospholipids, members of this family are directly regulated by phosphoinositides (PIPs) in the absence of other proteins or downstream signaling pathways. Different Kir isoforms display distinct specificities for the activating PIPs but all eukaryotic Kir channels are activated by PI(4,5)P2. On the other hand, the bacterial KirBac1.1 channel is inhibited by PIPs. Recent crystal structures of eukaryotic Kir channels in apo and lipid bound forms reveal one specific binding site per subunit, formed at the interface of N- and C-terminal domains, just beyond the transmembrane segments and clearly involving some of the key residues previously identified as controlling PI(4,5)P2 sensitivity. Computational, biochemical, and biophysical approaches have attempted to address the energetic determinants of PIP binding and selectivity among Kir channel isoforms, as well as the conformational changes that trigger channel gating. Here we review our current understanding of the molecular determinants of PIP regulation of Kir channel activity, including in context with other lipid modulators, and provide further discussion on the key questions that remain to be answered.

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Stoichiometry of Kir channels with phosphatidylinositol bisphosphate

Cited by 12 publications

References 49 publications

Distinct subunit contributions to the activation of M-type potassium channels by PI(4,5)P2

Distinct subunit contributions to the activation of M-type potassium channels by PI(4,5)P2

Phosphoinositide Control of Membrane Protein Function: A Frontier Led by Studies on Ion Channels

Phosphoinositide regulation of inward rectifier potassium (Kir) channels

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