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30-396: 16536 ENSG00000075043 ENSG00000281151 ENSMUSG00000016346 O43526 Q9Z351 NM_001382235 NM_001006675 NM_001006676 NM_001006677 NM_001006678 NM_001006679 NM_001006680 NM_010611 NM_001302888 NP_001369164 NP_001289817 NP_034741 K v 7.2 (KvLQT2) is a voltage- and lipid-gated potassium channel protein coded for by
60-423: A Kd much weaker than the bulk concentration in the membrane. Combined these data show that PA must be local in concentration near 100 micro molar or more, suggesting the diffusion of the lipid is somehow restricted in the membrane. In theory, ion channels can be activated by their diffusion or trafficking to high concentrations of a signaling lipid. The mechanism is similar to producing local high concentrations of
90-440: A decrease in this slow delayed potassium rectifier current, longer cardiac action potentials, and a tendency to have tachyarrhythmias. KCNE1 (minK), can assemble with KvLQT1 to form a slow delayed potassium rectifier channel. KCNE1 slows the inactivation of KvLQT1 when the two proteins form a heteromeric complex, and the current amplitude is greatly increased compared to WT-KvLQT1 homotetrameric channels. KCNE1 associates with
120-448: A membrane, the ligand was thought to diffuse away much to fast to activate a channel. However, Comoglio and colleagues showed experimentally that the enzyme phospholipase D2 bound directly to TREK-1 and produced the PA necessary to activate the channel. The conclusion of Comoglio et al was experimentally confirmed when it was shown that the dissociation constant of PA for TREK-1 is 10 micro molar,
150-516: A novel anti-convulsant drug. Defects in this gene are a cause of benign familial neonatal convulsions type 1 (BFNC), also known as epilepsy, benign neonatal type 1 (EBN1). At least five transcript variants encoding five different isoforms have been found for this gene. This article incorporates text from the United States National Library of Medicine , which is in the public domain . This membrane protein –related article
180-541: A process called transphoshatidylation. The PEth competes with PA and the competition antagonizes TREK-1 channels. The competition of PEth on potassium channel is thought to contribute to the anesthetic effect of ethanol and perhaps hangover. KvLQT1 3BJ4 , 3HFC , 3HFE , 4UMO , 4V0C 3784 16535 ENSG00000282076 ENSG00000053918 ENSMUSG00000009545 P51787 P97414 NM_181798 NM_000218 NM_181797 NM_008434 NP_000209 NP_861463 NP_032460 K v 7.1 ( KvLQT1 )
210-503: A signaling lipid, but instead of changing the concentration of the lipid in the membrane near the channel, the channel moves to a region of the plasma membrane that already contains high concentrations of a signaling lipid. The change the channel experiences in lipid composition can be much faster and without any change in the total lipid concentration in the membrane. Anionic lipids compete for binding sites within ion channel. Similar to neurotransmitters, competition of an antagonist reverses
240-456: A site in the transmembrane domain caused a conformational change that appeared to open the conduction pathway, suggesting the channel is classically lipid-gated. A PIP 2 compatible site was found in TRPV1 but whether the lipid alone can gate the channels has not been shown. Other TRP channels that directly bind PIP 2 are TRPM8 and TRPML. Direct binding does not exclude PIP 2 from affecting
270-465: Is a potassium channel protein whose primary subunit in humans is encoded by the KCNQ1 gene . It's mutation causes Long QT syndrome , K v 7.1 is a voltage and lipid-gated potassium channel present in the cell membranes of cardiac tissue and in inner ear neurons among other tissues. In the cardiac cells , K v 7.1 mediates the I Ks (or slow delayed rectifying K ) current that contributes to
300-459: Is a stub . You can help Misplaced Pages by expanding it . Lipid-gated ion channels Lipid-gated ion channels are a class of ion channels whose conductance of ions through the membrane depends directly on lipids . Classically the lipids are membrane resident anionic signaling lipids that bind to the transmembrane domain on the inner leaflet of the plasma membrane with properties of a classic ligand. Other classes of lipid-gated channels include
330-540: Is a cell membrane lipid, and its role in gating ion channels represents a novel role for the molecule. K ir channels : PIP 2 binds to and directly activates inwardly rectifying potassium channels (K ir ). The lipid binds in a well-defined ligand binding site in the transmembrane domain and causes the helices to splay opening the channel. All members of the K ir super-family of potassium channels are thought to be directly gated by PIP. K v 7 channels : PIP 2 binds to and directly activates K v 7.1 . In
SECTION 10
#1732883943108360-584: Is always found in native tissues with a modulatory subunit. In cardiac tissue, these subunits comprise KCNE1 and yotiao. Though physiologically irrelevant, homotetrameric K v 7.1 channels also display a unique form of C-type inactivation that reaches equilibrium quickly, allowing KvLQT1 currents to plateau. This is different from the inactivation seen in A-type currents, which causes rapid current decay. KvLQT1 has been shown to interact with PRKACA , PPP1CA and AKAP9 . KvLQT1 can also associate with any of
390-447: Is not well studied, but PLD can produce PG in the presence of glycerol suggesting the same mechanism that is thought to generate local PA gradients could be generating high local PG gradients as well. GLIC : The lipid phosphatidylcholine (PC) binds to the outer leaflet of the gleobacter ligad-gated ion channel ( GLIC and opens. General anesthetic propofol binds to the same region of the protein as PC. The competition of propofol with
420-639: The gene KCNQ2. Mutations in the KCNQ2 gene are dominant autosomally inherited causes of benign familial neonatal epilepsy . The M channel is a slowly activating and deactivating potassium channel that plays a critical role in the regulation of neuronal excitability. The M channel is formed by the association of the protein encoded by this gene and a related protein encoded by the KCNQ3 gene, both integral membrane proteins. M channel currents are inhibited by M1 muscarinic acetylcholine receptors and activated by retigabine ,
450-490: The repolarization of the cell, terminating the cardiac action potential and thereby the heart's contraction . It is a member of the KCNQ family of potassium channels. KvLQT1 is made of six membrane-spanning domains S1-S6, two intracellular domains, and a pore loop. The KvLQT1 channel is made of four KCNQ1 subunits, which form the actual ion channel. This gene encodes a protein for a voltage-gated potassium channel required for
480-492: The beta subunit, KCNE1, can lead to Long QT Syndrome or other cardiac rhythmic deformities. When associated with KCNE1, the KvLQT1 channel activates much more slowly and at a more positive membrane potential . It is believed that two KCNE1 proteins interact with a tetrameric KvLQT1 channel, since experimental data suggests that there are 4 alpha subunits and 2 beta subunits in this complex. KVLQT1/KCNE1 channels are taken up from
510-460: The channel absent a change in voltage suggesting these channels may also be lipid-gated. PA lipids were proposed to non-specifically gated a homologous channel from bacteria KvAP, but those experiments did not rule out the anionic lipid phosphatidylglycerol from contributing specifically to gating. Phosphatidylglycerol (PG) is an anionic lipid that activates many channels including most of the PA activated channels. The physiological signaling pathway
540-444: The channel by indirect mechanisms. Phosphatidic acid (PA) recently emerged as an activator of ion channels. K 2p : PA directly activates TREK-1 potassium channels through a putative site in the transmembrane domain. The affinity of PA for TREK-1 is relatively weak but the enzyme PLD2 produces high local concentration of PA to activate the channel. nAChR : PA also activates the nAChR in artificial membranes. Initially,
570-531: The current density at the plasma membrane of the neuron. In addition to associating with KCNE proteins, the N-terminal juxtamembranous domain of KvLQT1 can also associate with SGK1 , which stimulates the slow delayed potassium rectifier current. Since SGK1 requires structural integrity to stimulate KvLQT1/KCNE1, any mutations present in the KvLQT1 protein can result in reduced stimulation of this channel by SGK1. General mutations in KvLQT1 have been known to cause
600-434: The effect of an agonist. In most cases, the PA has the opposite effect of PIP2. Hence when PA binds to a channel that is activated by PIP2, PA inhibits the effect of PIP2. When PA activates the channel, PIP2 blocks the effect of PA inhibiting the channels. Ethanol When ethanol is consumed, phospholipase D incorporates the ethanol into phospholipids generating the unnatural and long lived lipid phosphatidylethanol (PEth) in
630-470: The five members of the KCNE family of proteins, but interactions with KCNE1 , KCNE2 , KCNE3 are the only interactions within this protein family that affect the human heart. KCNE2, KCNE4 , and KCNE5 have been shown to have an inhibitory effect on the functionality of KvLQT1, while KCNE1 and KCNE3 are activators of KvLQT1. KvLQT1 can associate with KCNE1 and KCNE4 with the activation effects of KCNE1 overriding
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#1732883943108660-565: The gene can lead to a defective protein and several forms of inherited arrhythmias as Long QT syndrome which is a prolongation of the QT interval of heart repolarization, Short QT syndrome , and Familial Atrial Fibrillation . KvLQT1 are also expressed in the pancreas, and KvLQT1 Long QT syndrome patients has been shown to have hyperinsulinemic hypoglycaemia following an oral glucose load. Currents arising from K v 7.1 in over-expression systems have never been recapitulated in native tissues - K v 7.1
690-473: The high concentration of PA required to activate nAChR suggested a related anionic lipid might activate the channel, however, the finding of local high concentration of PA activating TREK-1 may suggest otherwise. Kv : PA binding can also influence the midpoint of voltage activation (Vmid) for voltage-activated potassium channels. Depletion of PA shifted the Vmid -40 mV near resting membrane potential which could open
720-488: The inhibitory effects of KCNE4 on the KvLQT1 channel, and KvLQT1 will commonly associate with anywhere from two to four different KCNE proteins in order to be functional. However, KvLQT1 most commonly associates with KCNE1 and forms the KvLQT1/KCNE1 complex since it has only been seen to function in vivo when associated with another protein. KCNQ1 will form a heteromer with KCNE1 in order to slow its activation and enhance
750-467: The inner membrane of TREK-1 channels is thought to sense changes in membrane thickness and gate the channel. When an enzyme forms a complex with a channel it is thought to produce ligand near the channel in concentrations that are higher than the ligand in bulk membranes. Theoretical estimates suggest initial concentration of a signaling lipid produced near an ion channel are likely millimolar; however, due to theoretical calculations of lipids diffusion in
780-591: The lipid, i.e. displacement of the lipid, is thought to inhibit the channel. A specialized set of mechanosensitive ion channels is gated by lipid deformation in the membrane in response to mechanical force. A theory involving the lipid membrane, called "force from lipid", is thought to directly open ion channels. These channels include the bacterial channels MscL and MscS which open in response to lytic pressure. Many mechanosensitive channels require anionic lipids for activity. Channels can also respond to membrane thickness. An amphipathic helix that runs along
810-422: The mechanosensitive ion channels that respond to lipid tension, thickness, and hydrophobic mismatch. A lipid ligand differs from a lipid cofactor in that a ligand derives its function by dissociating from the channel while a cofactor typically derives its function by remaining bound. Phosphatidylinositol 4,5-bisphosphate (PIP 2 ) was the first and remains the best studied lipid to gate ion channels. PIP 2
840-577: The pore region of KvLQT1, and its transmembrane domain contributes to the selectivity filter of this heteromeric channel complex. The alpha helix of the KCNE1 protein interacts with the pore domain S5/S6 and with the S4 domain of the KvLQT1 channel. This results in structural modifications of the voltage sensor and the selectivity filter of the KvLQT1 channel. Mutations in either the alpha subunit of this complex, KvLQT1 or
870-496: The repolarization phase of the cardiac action potential. The gene product can form heteromultimers with two other potassium channel proteins, KCNE1 and KCNE3 . The gene is located in a region of chromosome 11 that contains a large number of contiguous genes that are abnormally imprinted in cancer and the Beckwith-Wiedemann syndrome . Two alternative transcripts encoding distinct isoforms have been described. Mutations in
900-423: The same study PIP 2 was shown to function as a ligand. When the channel was reconstituted into lipid vesicles with PIP 2 the channel opened, when PIP 2 was omitted the channel was closed. TRP channels : TRP channels were perhaps the first class of channels recognized as lipid-gated. PIP 2 regulates the conductance of most TRP channels either positively or negatively. For TRPV5, binding of PIP 2 to
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