Reciprocal modulation between the alpha and beta 4 subunits of hSlo calcium-dependent potassium channels

Large conductance Ca(2+)-dependent potassium (K(Ca) or maxi K) channels are composed of a pore-forming alpha subunit and an auxiliary beta subunit. We have shown that the brain-specific beta4 subunit modulates the voltage dependence, activation kinetics, and toxin sensitivity of the hSlo channel (Weiger, T. M., Holmqvist, M. H., Levitan, I. B., Clark, F. T., Sprague, S., Huang, W. J., Ge, P., Wang, C., Lawson, D., Jurman, M. E., Glucksmann, M. A., Silos-Santiago, I., DiStefano, P. S., and Curtis, R. (2000) J. Neurosci. 20, 3563-3570). We investigated here the N-linked glycosylation of the beta4 subunit and its effect on the modulation of the hSlo alpha subunit. When expressed alone in HEK293 cells, the beta4 subunit runs as a single molecular weight band on an SDS gel. However, when coexpressed with the hSlo alpha subunit, the beta4 subunit appears as two different molecular weight bands. Enzymatic deglycosylation or mutation of the N-linked glycosylation residues in beta4 converts it to a single lower molecular weight band, even in the presence of the hSlo alpha subunit, suggesting that the beta4 subunit can be present as an immature, core glycosylated form and a mature, highly glycosylated form. Blockage of protein transport from the endoplasmic reticulum to the Golgi compartment with brefeldin A abolishes the mature, highly glycosylated beta4 band. Glycosylation of the beta4 subunit is not required for its binding to the hSlo channel alpha subunit. It also is not necessary for cell membrane targeting of the beta4 subunit, as demonstrated by surface biotinylation experiments. However, the double glycosylation site mutant beta4 (beta4 N53A/N90A) protects the channel less against toxin blockade, as compared with the hSlo channel coexpressed with wild type beta4 subunit. Taken together, these data show that the pore-forming alpha subunit of the hSlo channel promotes N-linked glycosylation of its auxiliary beta4 subunit, and this in turn influences the modulation of the channel by the beta4 subunit.     

Intermolecular functional coupling between phosphoinositides and the potassium channel KcsA

Biological membranes are composed of a wide variety of lipids. Phosphoinositides (PIPns) in the membrane inner leaflet only account for a small percentage of the total membrane lipids but modulate the functions of various membrane proteins, including ion channels, which play important roles in cell signaling. KcsA, a prototypical K⁺ channel that is small, simple, and easy to handle, has been broadly examined regarding its crystallography, in silico molecular analysis, and electrophysiology. It has been reported that KcsA activity is regulated by membrane phospholipids, such as phosphatidylglycerol. However, there has been no quantitative analysis of the correlation between direct lipid binding and the functional modification of KcsA, and it is unknown whether PIPns modulate KcsA function. Here, using contact bubble bilayer recording, we observed that the open probability of KcsA increased significantly (from about 10% to 90%) when the membrane inner leaflet contained only a small percentage of PIPns. In addition, we found an increase in the electrophysiological activity of KcsA correlated with a larger number of negative charges on PIPns. We further analyzed the affinity of the direct interaction between PIPns and KcsA using microscale thermophoresis and observed a strong correlation between direct lipid binding and the functional modification of KcsA. In conclusion, our approach was able to reconstruct the direct modification of KcsA by PIPns, and we propose that it can also be applied to elucidate the mechanism of modification of other ion channels by PIPns.     

Proteolytic activation of a hyperpolarization- and calcium-dependent potassium channel inParamecium

Summary The effects of proteolysis on a hyperpolarization- and Ca²⁺-dependent K channel from the surface membrane ofParamecium tetraurelia were examined in the inside-out excised patch mode. Treatment with trypsin, pronase or thermolysin removed the Ca²⁺-dependence of the channel activation, yielding an increase in channel activity greater than 2.5-fold at all Ca²⁺ concentrations between 10^–4 and 10^–8 m. Thermolysin addition-ally removed the voltage dependence of channel opening and gave the most activation among the three proteases tested. Proteolysis did not affect the single-channel conductance. In an analogy to the mechanism of activation of many Ca²⁺-dependent enzymes it is suggested that thisParamecium channel has a cytoplasmic inhibitory domain which can be removed by proteolysis, and that the physiological activation by Ca²⁺ is due to a temporary removal of this inhibition. Moreover, these findings indicate structural differences between depolarization-, Ca²⁺-dependent K channels (BK channels) and the hyperpolarization-, Ca²⁺-dependent K channels inParamecium.     

Four-turn alpha-helical segment prevents surface expression of the auxiliary hbeta2 subunit of BK-type channel

Large conductance, voltage- and Ca2+-activated K+ (BK) channels encoded by the mslo alpha and beta2 subunits exist abundantly in rat chromaffin cells, pancreatic beta cells, and DRG neurons. The extracellular loop of hbeta2 acting as the channel regulator influences the rectification and toxin sensitivity of BK channels, and the inactivation domain at its N terminus induces rapid inactivation. However, the regulatory mechanism, especially the trafficking mechanism of hbeta2, is still unknown. With the help of immunofluorescence and patch clamp techniques, we determine that the hbeta2 subunit alone resides in the endoplasmic reticulum, suggesting that trafficking mechanism of hbeta2 differs from that of hbeta1 opposite to what we predicted previously. We further demonstrate that a four-turn alpha helical segment at the N terminus of hbeta2 prevents the surface expression of hbeta2, that is, the helical segment itself is a retention signal. Using the c-Myc epitope-tagged extracellular loop of hbeta2, we reveal that the most accessible site by antibody is located at the middle of the extracellular loop, which might provide clues to understand how the auxiliary beta subunits regulates the toxin sensitivity and the rectification of BK-type channels.     

Kv beta subunit oxidoreductase activity and Kv1 potassium channel trafficking.

Voltage-gated Kv1 potassium channels consist of pore-forming alpha subunits and cytoplasmic Kv beta subunits. The latter play diverse roles in modulating the gating, stability, and trafficking of Kv1 channels. The crystallographic structure of the Kv beta2 subunit revealed surprising structural homology with aldo-keto reductases, including a triosephosphate isomerase barrel structure, conservation of key catalytic residues, and a bound NADP(+) cofactor (Gulbis, J. M., Mann, S., and MacKinnon, R. (1999) Cell 90, 943-952). Each Kv1-associated Kv beta subunit (Kv beta 1.1, Kv beta 1.2, Kv beta 2, and Kv beta 3) shares striking amino acid conservation in key catalytic and cofactor binding residues. Here, by a combination of structural modeling and biochemical and cell biological analyses of structure-based mutations, we investigate the potential role for putative Kv beta subunit enzymatic activity in the trafficking of Kv1 channels. We found that all Kv beta subunits promote cell surface expression of coexpressed Kv1.2 alpha subunits in transfected COS-1 cells. Kv beta1.1 and Kv beta 2 point mutants lacking a key catalytic tyrosine residue found in the active site of all aldo-keto reductases have wild-type trafficking characteristics. However, mutations in residues within the NADP(+) binding pocket eliminated effects on Kv1.2 trafficking. In cultured hippocampal neurons, Kv beta subunit coexpression led to axonal targeting of Kv1.2, recapitulating the Kv1.2 localization observed in many brain neurons. Similar to the trafficking results in COS-1 cells, mutations within the cofactor binding pocket reduced axonal targeting of Kv1.2, whereas those in the catalytic tyrosine did not. Together, these data suggest that NADP(+) binding and/or the integrity of the binding pocket structure, but not catalytic activity, of Kv beta subunits is required for intracellular trafficking of Kv1 channel complexes in mammalian cells and for axonal targeting in neurons.     

Temperature dependence of drug blockade of a calcium-dependent potassium channel in cultured hippocampal neurons.

The temperature dependence of drug blockade of a calcium-dependent potassium channel K(Ca) has been studied in cultured CA1 hippocampal neurons. Channel openings from a 70-pS K+ channel were recorded when inside-out patches were exposed to a bath solution containing 140 mM K+ and 0.2 mM Ca2+. The mean open times of channel events were not significantly altered when the bath temperature was lowered from 24 degrees to 14 degrees C (Q10 = 1.2). Introduction of the drug RP-62719 into the bath solution (at 5 microM) resulted in the mean open time of the K(Ca) channel to be diminished by 85% (at 24 degrees C) with no change in the amplitudes of the unitary currents. Over the same temperature range of 24 degrees to 14 degrees C, in the presence of RP-62719, the mean open times were significantly prolonged (Q10 = 2.2). A simple open channel block scheme was used to determine the temperature dependence of the onward- (blocking) and off- (unblocking) rate constants. Thermodynamic analysis, using transition rate theory, showed that the blocking rate constant was associated with a large increase in entropy. The relatively high temperature dependence for channel blockade is not consistent with a rate-limiting process established by simple diffusion of the agent to a channel blocking site. Channel block may involve conformational changes in the channel protein as a consequence of hydrophobic interactions between drug and channel sites.     

Kinase-dependent regulation of the intermediate conductance, calcium-dependent potassium channel, hIK1

We determined the effect of nucleotides and protein kinase A (PKA) on the Ca(2+)-dependent gating of the cloned intermediate conductance, Ca(2+)-dependent K(+) channel, hIK1. In Xenopus oocytes, during two-electrode voltage-clamp, forskolin plus isobutylmethylxanthine induced a Ca(2+)-dependent increase in hIK1 activity. In excised inside-out patches, addition of ATP induced a Ca(2+)-dependent increase in hIK1 activity (NP(o)). In contrast, neither nonhydrolyzable (AMP-PNP, AMP-PCP) nor hydrolyzable ATP analogs (GTP, CTP, UTP, and ITP) activated hIK1. The ATP-dependent activation of hIK1 required Mg(2+) and was reversed by either exogenous alkaline phosphatase or the PKA inhibitor PKI(5-24). The Ca(2+) dependence of hIK1 activation was best fit with a stimulatory constant (K(s)) of 350 nM and a Hill coefficient (n) of 2.3. ATP increased NP(o) at [Ca(2+)] >100 nM while having no effect on K(s) or n. Mutation of the single PKA consensus phosphorylation site at serine 334 to alanine (S334A) had no effect on the PKA-dependent activation during either two-electrode voltage-clamp or in excised inside-out patches. When expressed in HEK293 cells, ATP activated hIK1 in a Mg(2+)-dependent fashion, being reversed by alkaline phosphatase. Neither PKI(5-24) nor CaMKII(281-309) or PKC(19-31) affected the ATP-dependent activation. Northern blot analysis revealed hIK1 expression in the T84 colonic cell line. Endogenous hIK1 was activated by ATP in a Mg(2+)- and PKI(5-24)-dependent fashion and was reversed by alkaline phosphatase, whereas CaMKII(281-309) and PKC(19-31) had no effect on the ATP-dependent activation. The Ca(2+)-dependent activation (K(s) and n) was unaffected by ATP. In conclusion, hIK1 is activated by a membrane delimited PKA when endogenously expressed. Although the oocyte expression system recapitulates this regulation, expression in HEK293 cells does not. The effect of PKA on hIK1 gating is Ca(2+)-dependent and occurs via an increase in NP(o) without an effect on either Ca(2+) affinity or apparent cooperativity.     

Mitochondrial ATP-sensitive potassium channel activity and hypoxic preconditioning are independent of an inwardly rectifying potassium channel subunit in Caenorhabditis elegans

Hypoxic preconditioning (HP) is an evolutionarily-conserved mechanism that protects an organism against stress. The mitochondrial ATP-sensitive K(+) channel (mK(ATP)) plays an essential role in the protective signaling, but remains molecularly undefined. Several lines of evidence suggest that mK(ATP) may arise from an inward rectifying K(+) channel (Kir). The genetic model organism Caenorhabditis elegans exhibits HP and displays mK(ATP) activity. Here, we investigate the tissue expression profile of the three C. elegans Kir genes and demonstrate that mutant strains where the irk genes have been deleted either individually or in combination can be protected by HP and exhibit robust mK(ATP) channel activity in purified mitochondria. These data suggest that the mK(ATP) in C. elegans does not arise from a Kir derived channel.     

The sigma receptor as a ligand-regulated auxiliary potassium channel subunit

The sigma receptor is a novel protein that mediates the modulation of ion channels by psychotropic drugs through a unique transduction mechanism depending neither on G proteins nor protein phosphorylation. The present study investigated sigma receptor signal transduction by reconstituting responses in Xenopus oocytes. Sigma receptors modulated voltage-gated K+ channels (Kv1.4 or Kv1.5) in different ways in the presence and absence of ligands. Association between Kv1.4 channels and sigma receptors was demonstrated by coimmunoprecipitation. These results indicate a novel mechanism of signal transduction dependent on protein-protein interactions. Domain accessibility experiments suggested a structure for the sigma receptor with two cytoplasmic termini and two membrane-spanning segments. The ligand-independent effects on channels suggest that sigma receptors serve as auxiliary subunits to voltage-gated K+ channels with distinct functional interactions, depending on the presence or absence of ligand.     

Molecular cloning and functional expression of KCNQ5, a potassium channel subunit that may contribute to neuronal M-current diversity

We have isolated KCNQ5, a novel human member of the KCNQ potassium channel gene family that is differentially expressed in subregions of the brain and in skeletal muscle. When expressed in Xenopus oocytes, KCNQ5 generated voltage-dependent, slowly activating K(+)-selective currents that displayed a marked inward rectification at positive membrane voltages. KCNQ5 currents were insensitive to the K(+) channel blocker tetraethylammonium but were strongly inhibited by the selective M-current blocker linopirdine. Upon coexpression with the structurally related KCNQ3 channel subunit, current amplitudes increased 4-5-fold. Compared with homomeric KCNQ5 currents, KCNQ3/KCNQ5 currents also displayed slower activation kinetics and less inward rectification, indicating that KCNQ5 combined with KCNQ3 to form functional heteromeric channel proteins. This functional interaction between KCNQ5 and KCNQ3, a component of the M-channel, suggests that KCNQ5 may contribute to a diversity of heteromeric channels underlying native neuronal M-currents.     

Molecular diversity and functional evolution of scorpion potassium channel toxins

Scorpion toxins affecting K(+) channels (KTxs) represent important pharmacological tools and potential drug candidates. Here, we report molecular characterization of seven new KTxs in the scorpion Mesobuthus eupeus by cDNA cloning combined with biochemical approaches. Comparative modeling supports that all these KTxs share a conserved cysteine-stabilized α-helix/β-sheet structural motif despite the differences in protein sequence and size. We investigated functional diversification of two orthologous α-KTxs (MeuTXKα1 from M. eupeus and BmP01 from Mesobuthus martensii) by comparing their K(+) channel-blocking activities. Pharmacologically, MeuTXKα1 selectively blocked Kv1.3 channel with nanomolar affinity (IC(50), 2.36 ± 0.9 nM), whereas only 35% of Kv1.1 currents were inhibited at 3 μM concentration, showing more than 1271-fold selectivity for Kv1.3 over Kv1.1. This peptide displayed a weak effect on Drosophila Shaker channel and no activity on Kv1.2, Kv1.4, Kv1.5, Kv1.6, and human ether-a-go-go-related gene (hERG) K(+) channels. Although BmB01 and MeuTXKα1 have a similar channel spectrum, their affinity and selectivity for these channels largely varies. In comparison with MeuTXKα1, BmP01 only exhibits a submicromolar affinity (IC(50), 133.72 ± 10.98 nM) for Kv1.3, showing 57-fold less activity than MeuTXKα1. Moreover, it lacks the ability to distinguish between Kv1.1 and Kv1.3. We also found that MeuTXKα1 inhibited the proliferation of activated T cells induced by phorbol myristate acetate and ionomycin at micromolar concentrations. Our results demonstrate that accelerated evolution drives affinity variations of orthologous α-KTxs on Kv channels and indicate that MeuTXKα1 is a promising candidate to develop an immune modulation agent for human autoimmune diseases.     

Tuning the tetraethylammonium sensitivity of potassium channel Kcv by subunit combination

Tetraethylammonium (TEA) is a potassium (K(+)) channel inhibitor that has been extensively used as a molecular probe to explore the structure of channels' ion pathway. In this study, we identified that Leu70 of the virus-encoded potassium channel Kcv is a key amino acid that plays an important role in regulating the channel's TEA sensitivity. Site-directed mutagenesis of Leu70 can change the TEA sensitivity by 1,000-fold from ～100 μM to ～100 mM. Because no compelling trends exist to explain this amino acid's specific interaction with TEA, the role of Leu70 at the binding site is likely to ensure an optimal conformation of the extracellular mouth that confers high TEA affinity. We further assembled the subunits of mutant and wt-Kcv into a series of heterotetramers. The differences in these heterochannels suggest that all of the four subunits in a Kcv channel additively participate in the TEA binding, and each of the four residues at the binding site independently contributes an equal binding energy. We therefore can present a series of mutant/wild-type tetramer combinations that can probe TEA over three orders of magnitude in concentration. This study may give insight into the mechanism for the interaction between the potassium channel and its inhibitor.     

Structural and functional diversity of acidic scorpion potassium channel toxins

Background

Although the basic scorpion K⁺ channel toxins (KTxs) are well-known pharmacological tools and potential drug candidates, characterization the acidic KTxs still has the great significance for their potential selectivity towards different K⁺ channel subtypes. Unfortunately, research on the acidic KTxs has been ignored for several years and progressed slowly.

Principal Findings

Here, we describe the identification of nine new acidic KTxs by cDNA cloning and bioinformatic analyses. Seven of these toxins belong to three new α-KTx subfamilies (α-KTx28, α-KTx29, and α-KTx30), and two are new members of the known κ-KTx2 subfamily. ImKTx104 containing three disulfide bridges, the first member of the α-KTx28 subfamily, has a low sequence homology with other known KTxs, and its NMR structure suggests ImKTx104 adopts a modified cystine-stabilized α-helix-loop-β-sheet (CS-α/β) fold motif that has no apparent α-helixs and β-sheets, but still stabilized by three disulfide bridges. These newly described acidic KTxs exhibit differential pharmacological effects on potassium channels. Acidic scorpion toxin ImKTx104 was the first peptide inhibitor found to affect KCNQ1 channel, which is insensitive to the basic KTxs and is strongly associated with human cardiac abnormalities. ImKTx104 selectively inhibited KCNQ1 channel with a K_d of 11.69 µM, but was less effective against the basic KTxs-sensitive potassium channels. In addition to the ImKTx104 toxin, HeTx204 peptide, containing a cystine-stabilized α-helix-loop-helix (CS-α/α) fold scaffold motif, blocked both Kv1.3 and KCNQ1 channels. StKTx23 toxin, with a cystine-stabilized α-helix-loop-β-sheet (CS-α/β) fold motif, could inhibit Kv1.3 channel, but not the KCNQ1 channel.

Conclusions/Significance

These findings characterize the structural and functional diversity of acidic KTxs, and could accelerate the development and clinical use of acidic KTxs as pharmacological tools and potential drugs.     

AMIGO is an auxiliary subunit of the Kv2.1 potassium channel

Kv2.1 is a potassium channel α-subunit abundantly expressed throughout the brain. It is a main component of delayed rectifier current (I(K)) in several neuronal types and a regulator of excitability during high-frequency firing. Here we identify AMIGO (amphoterin-induced gene and ORF), a neuronal adhesion protein with leucine-rich repeat and immunoglobin domains, as an integral part of the Kv2.1 channel complex. AMIGO shows extensive spatial and temporal colocalization and association with Kv2.1 in the mouse brain. The colocalization of AMIGO and Kv2.1 is retained even during stimulus-induced changes in Kv2.1 localization. AMIGO increases Kv2.1 conductance in a voltage-dependent manner in HEK cells. Accordingly, inhibition of endogenous AMIGO suppresses neuronal I(K) at negative membrane voltages. In conclusion, our data indicate AMIGO as a function-modulating auxiliary subunit for Kv2.1 and thus provide new insights into regulation of neuronal excitability.     

Activation process of calcium-dependent potassium channel in Euhadra neurons: involvement of calcium/calmodulin and subsequent protein phosphorylation.

1. The activation process of Ca(2+)-dependent potassium channel was studied electrophysiologically and pharmacologically using identified neurons of the land snail, Euhadra peliomphala. 2. Ca(2+)-mediated delayed outward K current (IKD) was dose-dependently reduced by the calmodulin inhibitors, N-(6-aminohexyl)-1-naphthalenesulfonamide (W-5, week) and N-(6-aminohexyl)-5-chloro-naphthalenesulfonamide (W-7, potent). These antagonists also caused a slight membrane depolarization and increase in impulse discharge frequency with decrease in the amplitude of both action potential and after hyperpolarization. 3. The cAMP-dependent protein kinase inhibitor N-[2-(methylamino) ethyl]-5-isoquinoline-sulfonamide (H-8) did not produce any significant effect on IKD and membrane potential. 4. Calmodulin, when injected into the neuron which had been treated with either W-5 or W-7, transiently restored the suppressed IKD nearly to the pretreatment level, and caused hyperpolarization of the cell. In contrast, calcium chloride, intracellularly injected in the same way, had little effect on both the IKD and the membrane potential shifted by these antagonists. 5. Intracellular injection of kinase II, a Ca2+/calmodulin-dependent protein kinase, caused an increase in the IKD and membrane hyperpolarization. Similar but weak effects were produced when a catalytic subunit (CS) of cAMP-dependent protein kinase was intracellularly injected. However, the neurons pretreated with W-7 no longer had any detectable increase in the IKD and hyperpolarization of the membrane. 6. These results suggest the possibility that Ca2+/camodulin-dependent protein phosphorylation may finally mediate the activation of a certain number of potassium channels.     

Direct interaction and functional coupling between voltage-gated CaV1.3 Ca channel and GABAB receptor subunit 2

Although Ca_V1.2 and Ca_V1.3 are two subtypes of L-type Ca²⁺ channels expressed in the CNS, functions of Ca_V1.3 have not been well elucidated compared to Ca_V1.2. Here, we found that Ca_V1.3-NT associates with GABA_BR2-CT using yeast two-hybrid, GST pull-down and co-immunoprecipitation assays. We also demonstrated co-localization of Ca_V1.3 and GABA_BR2 in HEK293 cells and cultured hippocampal neurons. Whole-cell patch-clamp and Ca²⁺-imaging experiments revealed that activation of GABA_BR increases Ca_V1.3 currents and intracellular Ca²⁺ via Ca_V1.3, but not Ca_V1.2. These results show a physical and functional interaction between Ca_V1.3 and GABA_BR, suggesting the potential pivotal roles of Ca_V1.3 in the CNS.

Structured summary

MINT-7975667: Cav1.3 (uniprotkb:P27732) physically interacts (MI:0915) with GABABR2 (uniprotkb:O88871) by two hybrid (MI:0018)MINT-7975740: Cav1.3 (uniprotkb:P27732) and GABABR2 (uniprotkb:O75899) colocalize (MI:0403) by fluorescence microscopy (MI:0416)MINT-7966007, MINT-7966016: Cav1.3 (uniprotkb:P27732) physically interacts (MI:0915) with GABABR2 (uniprotkb:O88871) by anti bait coimmunoprecipitation (MI:0006)MINT-7975712, MINT-7975691: Cav1.3 (uniprotkb:P27732) physically interacts (MI:0915) with GABABR2 (uniprotkb:O88871) by pull down (MI:0096)MINT-7966026: GABABR2 (uniprotkb:O88871) and Cav1.3 (uniprotkb:P27732) colocalize (MI:0403) by fluorescence microscopy (MI:0416)     

Phosphorylation-dependent interactions of alpha-Actinin-1/IQGAP1 with the AMPA receptor subunit GluR4

AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors play key roles in excitatory synaptic transmission and synaptic plasticity in the CNS. Although a variety of proteins has been characterized to interact with AMPA receptors and regulate their function, little is known about the regulation of the AMPA receptor subunit GluR4. To understand the molecular mechanisms of GluR4 functional regulation, the yeast two-hybrid system was used to identify GluR4-interacting molecules. alpha-Actinin-1 and IQGAP1 were identified to be GluR4-specific binding partners. Both proteins interact specifically with GluR4 and co-cluster with GluR4 individually in neurons. Mapping experiments revealed that alpha-Actinin-1 and IQGAP1 bind to the same region within the C-terminus of GluR4 that contains a previously identified PKA phosphorylation site, Ser842, phosphorylation of which is regulated by synaptic activity. Interestingly, the phosphorylation of Ser842 differentially regulates interactions of GluR4 with alpha-Actinin-1 and IQGAP1; phosphorylation strongly inhibits interaction of GluR4 with alpha-Actinin-1 but has little effect on its interaction with IQGAP1. These results suggest that alpha-Actinin-1 and IQGAP1 regulate GluR4 functions via their specific associations with GluR4. In addition, our data indicate that activity-dependent phosphorylation of GluR4 may regulate its synaptic targeting through phosphorylation-dependent interactions with alpha-Actinin-1 and IQGAP1.     

Cloning and functional expression of a TEA-sensitive A-type potassium channel from rat brain.

A rat brain cDNA (Raw3) related to the Drosophila Shaw K+ channel family has been characterized. Raw3 cRNA leads to the formation of TEA-insensitive, fast inactivating (A-type) K+ channels when injected into Xenopus laevis oocytes. Raw3 channels have markedly different properties from the previously cloned rat A-type K+ channel RCK4, Raw3 channels operate in the positive voltage range.     

The viral potassium channel Kcv: structural and functional features

The chlorella virus PBCV-1 was the first virus found to encode a functional potassium channel protein (Kcv). Kcv is small (94 aa) and basically consists of the M1-P-M2 (membrane-pore-membrane) module typical of the pore regions of all known potassium channels. Kcv forms functional channels in three heterologous systems. This brief review discusses the gating, permeability and modulation properties of Kcv and compares them to the properties of bacterial and mammalian K+ channels.