Phosphatidylinositol 4,5-Bisphosphate and Intracellular pH Regulate the ROMK1 Potassium Channel via Separate but Interrelated Mechanisms

Leung, Yuk‐Man; Zeng, Wei; Liou, Horng-Huei; Solaro, Christopher R.; Huang, Chou Long

doi:10.1074/jbc.275.14.10182

Cited by 71 publications

(89 citation statements)

References 32 publications

(70 reference statements)

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“…It has been shown that reduction in PIP 2 binding can shift the effective pK a for pH gating in Kir1.1 channels to more alkaline values. This was based on the finding that low PIP 2 concentrations in the membrane or reduction in PIP 2 binding, as seen with a mutant channel (R188Q), increased the pH sensitivity (15). We found that PIP 2 binding is already saturated for WT Kir1.1 channels since addition of exogenous PIP 2 caused no additional shift in the pK a .…”

Section: Arg-54 In the N Terminus Of Kir62 Is A Major Determinant Fomentioning

confidence: 99%

“…It has been proposed that PIP 2 binding to Kir1.1 alters the pK a for pH gating (15). Thus, we tested whether the absence of the N-terminal PIP 2 site might be a prerequisite for Kir1.1 channels to operate in the physiological pH range (6.8 -7.5).…”

Section: Arg-54 In the N Terminus Of Kir62 Is A Major Determinant Fomentioning

confidence: 99%

“…In addition, PIPs were shown to interfere with the different gating mechanisms of Kir channels. A recent report indicated modulation of pH sensitivity of Kir1.1 channels by PIP 2 since a mutation in the C terminus (R188Q) that reduced PIP 2 binding also changed the pH sensitivity (15). Further, PIPs are effective modulators of K ATP channels because they reduce the sensitivity to inhibition by intracellular ATP (12,13).…”

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confidence: 99%

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Phosphatidylinositol 4,5-Bisphosphate (PIP2) Modulation of ATP and pH Sensitivity in Kir Channels

Schulze¹,

Krauter²,

Fritzenschaft

et al. 2003

Journal of Biological Chemistry

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Phosphatidylinositol polyphosphates (PIPs) are potent modulators of Kir channels. Previous studies have implicated basic residues in the C terminus of Kir6.2 channels as interaction sites for the PIPs. Here we examined the role of the N terminus and identified an arginine (Arg-54) as a major determinant for PIP 2 modulation of ATP sensitivity in K ATP channels. Mutation of Arg-54 to the neutral glutamine (R54Q) and, in particular, to the negatively charged glutamate (R54E) impaired PIP 2 modulation of ATP inhibition, while mutation to lysine (R54K) had no effect. These data suggest that electrostatic interactions between PIP 2 and Arg-54 are an essential step for the modulation of ATP sensitivity. This N-terminal PIP 2 site is highly conserved in Kir channels with the exception of the pH-gated channels Kir1.1, Kir4.1, and Kir5.1 that contain a neutral residue at the corresponding positions. Introduction of an arginine at this position in Kir1.1 channels rendered the N-terminal PIP 2 site functional largely increasing the PIP 2 affinity. Moreover, Kir1.1 channels lose the ability to respond to physiological changes of the intracellular pH. These results explain the need of a silent N-terminal PIP 2 site in pH-gated channels and highlight the N terminus as an important region for PIP 2 modulation of Kir channel gating.Kir channels are a superfamily of eukaryotic channel proteins that are expressed in many tissues and responsible for important physiological processes such as cell excitability, insulin secretion, K ϩ homeostasis, vascular tone, and regulation of the heart rate. Four subunits assemble to a channel. Each subunit contains two transmembrane segments with cytoplasmic N-and C-terminal domains and a connecting loop forming the pore (1). Some members of the Kir channel family are endowed with gating mechanisms such as ATP gating (K ATP channels) (2) and pH gating (Kir1.1 and Kir4.1 channels) (3). These gating mechanisms are central for the diverse functions of Kir channels in physiology and the understanding of the related pathophysiology. Kir1, Kir4, and Kir5 channels, that are predominantly expressed in epithelia, are exquisitely sensitive to changes in intracellular pH in the physiological range (3-5). This pH sensitivity is mediated by the protonation of a lysine in the N terminus (Lys-80 in Kir1.1) that induces closure of the channel's pore by an allosteric mechanism (pH gating) (3, 6). Even small changes in the pH sensitivity can cause severe kidney defects such as the Bartter syndrome (3), highlighting the physiological importance of proper pH gating in Kir1.1 channels. Kir6 channels display a very ubiquitous expression pattern and, in coassembly with the sulfonylurea receptor (SUR), 1 represent the ATP-sensitive K ϩ channels (K ATP channels) (7). Intracellular ATP closes K ATP channels by binding to the Kir6.2 subunits (ATP gating), whereas the SURs act as regulatory subunits endowing the channel with sensitivity to MgADP and pharmacological compounds. The ATP/ADP dependence of K ATP channels couple...

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Section: Arg-54 In the N Terminus Of Kir62 Is A Major Determinant Fomentioning

confidence: 99%

Section: Arg-54 In the N Terminus Of Kir62 Is A Major Determinant Fomentioning

confidence: 99%

mentioning

confidence: 99%

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Phosphatidylinositol 4,5-Bisphosphate (PIP2) Modulation of ATP and pH Sensitivity in Kir Channels

Schulze¹,

Krauter²,

Fritzenschaft

et al. 2003

Journal of Biological Chemistry

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“…Activity of the Kir1.1 channel is directly regulated by intracellular pH, protein kinase A, protein kinase C, phosphatidylinositol-4,5-biphosphate, and WNK4 (serine-threonine kinase 4 with no lysine) (8 -11). Inhibition of protein kinase A activity or phosphatidylinositol-4,5-biphosphate production shifts the channel sensitivity toward more alkaline pH levels (12,13).…”

Section: Kir11 (Romk1) Is a Member Of The Inward Rectifier Kmentioning

confidence: 99%

Subunit Stoichiometry of the Kir1.1 Channel in Proton-dependent Gating

Wang

et al. 2005

Journal of Biological Chemistry

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Kir1.1 channel regulates membrane potential and K؉ secretion in renal tubular cells. This channel is gated by intracellular protons, in which a lysine residue (Lys 80 ) plays a critical role. Mutation of the Lys 80 to a methionine (K80M) disrupts pH-dependent channel gating. To understand how an individual subunit in a tetrameric channel is involved in pH-dependent channel gating, we performed these studies by introducing K80M-disrupted subunits to tandem tetrameric channels. The pH sensitivity was studied in whole-cell voltage clamp and inside-out patches. Homomeric tetramers of the wild-type (wt) and K80M-disrupted channels showed a pH sensitivity almost identical to that of their monomeric counterparts. In heteromeric tetramers and dimers, pH sensitivity was a function of the number of wt subunits. Recruitment of the first single wt subunit shifts the pK a greatly, whereas additions of any extra wt subunit had smaller effects. Single-channel analysis revealed that the tetrameric channel with two or more wt subunits showed one substate conductance at ϳ40% of the full conductance, suggesting that four subunits act as two pairs. However, three and four substates of conductance were seen in the tetrameric wt-3K80M and 4K80M channels. Acidic pH increased long-time closures when there were two or more wt subunits. Disruption of more than two subunits led to flicking activity with appearance of a new opening event and loss of the long period of closures. Interestingly, the channel with two wt subunits at diagonal and adjacent configurations showed the same pH sensitivity, substate conductance, and long-time closure. These results thus suggest that one functional subunit is sufficient to act in the pH-dependent gating of the Kir1.1 channel, the channel sensitivity to pH increases with additional subunits, the full pH sensitivity requires contributions of all four subunits, and two subunits may be coordinated in functional dimers of either trans or cis configuration.Kir1.1 (ROMK1) is a member of the inward rectifier K ϩ (Kir) channel family. A functional channel consists of four Kir subunits, and each Kir subunit has two membrane-spanning helices and a pore-forming sequence (1, 2). The Kir1.1 channel was originally cloned from the outer medulla of the kidney and later found in several other tissues (3, 4). The channel regulates K ϩ recycling in the thick ascending limb of Henle and K ϩ secretion in the cortical collecting duct (4, 5). Dysfunction of the Kir1.1 channel is one of the major causes for Bartter syndrome, which is characterized by decreased salt transport in the thick ascending limb of Henle (5). Kir1.1 surface expression and trafficking rely on protein kinase A and protein kinase C (6, 7). Activity of the Kir1.1 channel is directly regulated by intracellular pH, protein kinase A, protein kinase C, phosphatidylinositol-4,5-biphosphate, and WNK4 (serine-threonine kinase 4 with no lysine) (8 -11). Inhibition of protein kinase A activity or phosphatidylinositol-4,5-biphosphate production shifts the channel sen...

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“…For the TRPM7 channel, cation screening of membrane phosphatidylinositol(4,5)bisphosphate (PIP 2 ) charges appears to be important for polyvalent cation-mediated regulation of channel activity. Similarly, PIP 2 greatly influences the open state of ROMK, and this effect can be modulated by internal pH (6). Thus, multiple types of salt bridge interactions may be contributing to the very complex behavior of channels to changes in cytosolic pH.…”

Section: The C-terminal Arginine In the Rxr Forms An R-e Ion Pair Betmentioning

confidence: 99%

Subunit–subunit interactions are critical for proton sensitivity of ROMK: Evidence in support of an intermolecular gating mechanism

MacGregor

Dong

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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, and the gating of this channel is highly sensitive to changes in cytosolic pH. Although charge-charge interactions have been implicated in pH sensing by this K channel tetramer, the molecular mechanism linking pH sensing and the gating of ion channels is poorly understood. The x-ray crystal structure KirBac1.1, a prokaryotic ortholog of ROMK, has suggested that channel gating involves intermolecular interactions of the N-and C-terminal domains of adjacent subunits. Here we studied channel gating behavior to changes in pH using giant patch clamping of Xenopus laevis oocytes expressing WT or mutant ROMK, and we present evidence that no single charged residue provides the pH sensor. Instead, we show that N-C-and C-Cterminal subunit-subunit interactions form salt bridges, which function to stabilize ROMK in the open state and which are modified by protons. We identify a highly conserved C-C-terminal arginine-glutamate (R-E) ion pair that forms an intermolecular salt bridge and responds to changes in proton concentration. Our results support the intermolecular model for pH gating of inward rectifier K channels.channel gating ͉ inward rectifier ͉ Kir1.1 ͉ pH sensing ͉ potassium channel

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Phosphatidylinositol 4,5-Bisphosphate and Intracellular pH Regulate the ROMK1 Potassium Channel via Separate but Interrelated Mechanisms

Cited by 71 publications

References 32 publications

Phosphatidylinositol 4,5-Bisphosphate (PIP2) Modulation of ATP and pH Sensitivity in Kir Channels

Phosphatidylinositol 4,5-Bisphosphate (PIP2) Modulation of ATP and pH Sensitivity in Kir Channels

Subunit Stoichiometry of the Kir1.1 Channel in Proton-dependent Gating

Subunit–subunit interactions are critical for proton sensitivity of ROMK: Evidence in support of an intermolecular gating mechanism

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