A Protein With a Single Transmembrane Domain Forms an Ion Channel

Physiology ◽  
1993 ◽  
Vol 8 (4) ◽  
pp. 175-178 ◽  
Author(s):  
T Takumi
Keyword(s):  
Membrane Protein ◽  
Ion Channel ◽  
Transmembrane Domain ◽  
K Channel ◽  
Channel Activity ◽  
Single Membrane ◽  
Voltage Dependent ◽  
Membrane Spanning

Isk is a small membrane protein with a single membrane-spanning domain and shows a slow voltage-dependent K+ channel activity. Mutational analyses showed that Isk forms an integral part of the K+ channel itself. Two other proteins have similar properties, suggesting a new group of voltage-dependent channels.

scholarly journals Dislocation of a Type I Membrane Protein Requires Interactions between Membrane-spanning Segments within the Lipid Bilayer

2003 ◽  
Vol 14 (9) ◽  
pp. 3690-3698 ◽  
Author(s):  
Brendan N. Lilley ◽  
Domenico Tortorella ◽  
Hidde L. Ploegh
Keyword(s):  
Membrane Protein ◽  
Heavy Chain ◽  
Transmembrane Domain ◽  
Helical Structure ◽  
Type I ◽  
Rapid Degradation ◽  
Heavy Chains ◽  
Histocompatibility Complex ◽  
Subsequent Degradation ◽  
Membrane Spanning

The human cytomegalovirus gene product US11 causes rapid degradation of class I major histocompatibility complex (MHCI) heavy chains by inducing their dislocation from the endoplasmic reticulum (ER) and subsequent degradation by the proteasome. This set of reactions resembles the endogenous cellular quality control pathway that removes misfolded or unassembled proteins from the ER. We show that the transmembrane domain (TMD) of US11 is essential for MHCI heavy chain dislocation, but dispensable for MHCI binding. A Gln residue at position 192 in the US11 TMD is crucial for the ubiquitination and degradation of MHCI heavy chains. Cells that express US11 TMD mutants allow formation of MHCI-β2m complexes, but their rate of egress from the ER is significantly impaired. Further mutagenesis data are consistent with the presence of an alpha-helical structure in the US11 TMD essential for MHCI heavy chain dislocation. The failure of US11 TMD mutants to catalyze dislocation is a unique instance in which a polar residue in the TMD of a type I membrane protein is required for that protein's function. Targeting of MHCI heavy chains for dislocation by US11 thus requires the formation of interhelical hydrogen bonds within the ER membrane.

Differential distribution of potassium channels in acutely demyelinated, primary-auditory neurons in vitro

1996 ◽  
Vol 76 (1) ◽  
pp. 438-447 ◽  
Author(s):  
R. L. Davis
Keyword(s):  
Potassium Channels ◽  
Potassium Channel ◽  
Myelin Sheath ◽  
Lucifer Yellow ◽  
The Other ◽  
K Channel ◽  
Channel Activity ◽  
Auditory Neurons ◽  
Axonal Membrane ◽  
Voltage Dependent

1. Single-channel recordings of potassium channel activity were made from two populations of primary-auditory neurons maintained in tissue culture. The saccular nerve, which is the auditory component of the eighth cranial nerve in goldfish, was separated into two branches according to its peripheral innervation pattern. Neurons which innervated the rostral saccular macula corresponded to a class of cells that showed spike frequency adaptation; whereas, neurons which innervated the caudal macula were consistent with another type of cell that demonstrated bursting spontaneous firing patterns in vivo. Both somatic and internodal axonal membranes from each of these neuronal classes were studied after acute removal of the myelin sheath by microdissection. 2. Dye injections were used to discriminate neuronal from myelin membrane. After successful removal of the myelin, patch electrodes containing Lucifer yellow were used to fill a neuron and reveal its morphology within the myelin sheath. Patches on myelin led to filling of Schwann cells that surrounded the neuron. 3. Four kinds of potassium channels were observed and characterized according to unitary conductance, inactivation, and sensitivity to internal calcium. Three voltage-dependent K+ channel types were found on the somatic and axonal membrane of the two neuronal populations. Two channel types showed voltage-dependent inactivation and had average conductances of 32 and 19 pS, each with distinctive subconductance states. The third type of channel activity had an estimated conductance of 12 pS and was noninactivating. 4. The fourth type of channel was the Ca2(+)-activated K+ channel (k(Ca)), which was classified by the dependence of its activity on the calcium concentration at its cytoplasmic surface. Unlike the other three potassium channel types, this kind of channel was found exclusively on neurons that innervated the caudal sensory epithelium. As with the other kinds of potassium channels, it was found on both somatic and axonal internodal membranes.

ATP-sensitive K + -channel run-down is Mg 2+ dependent

1990 ◽  
Vol 240 (1298) ◽  
pp. 397-410 ◽  
Keyword(s):  
State Probability ◽  
K Channel ◽  
Channel Activity ◽  
Channel Current ◽  
Phosphatase Inhibitor ◽  
Voltage Dependent ◽  
Insulin Secreting Cells ◽  
Channel Currents

ATP-sensitive K + -channel currents were recorded from isolated mem­brane patches and voltage-clamped CRI-G1 insulin-secreting cells. Inter­nal Mg 2+ ions inhibited ATP-K + channels by a voltage-dependent block of the channel current and decrease of open-state probability. The run­ down of ATP-K + channel activity was also shown to be [Mg 2+ ] i depen­dent, being almost abolished in Mg 2+ -free conditions. Substitution of Mn 2+ for Mg 2+ did not prevent run-down, nor did the presence of phos­phate-donating nucleotides, a protease or phosphatase inhibitor or replacement of Cl by gluconate.

scholarly journals Immune Checkpoint Inhibitors Regulate K+ Channel Activity in Cytotoxic T Lymphocytes of Head and Neck Cancer Patients

2021 ◽  
Vol 12 ◽  
Author(s):  
Vaibhavkumar S. Gawali ◽  
Ameet A. Chimote ◽  
Hannah S. Newton ◽  
Manuel G. Feria-Garzón ◽  
Martina Chirra ◽  
...  
Keyword(s):  
T Cell ◽  
Ion Channel ◽  
Head And Neck ◽  
Immune Checkpoint ◽  
Cell Function ◽  
K Channel ◽  
Channel Activity ◽  
Crac Channels ◽  
T Cell Function ◽  
Intracellular Ca

Programmed death receptor-1 (PD-1) and its ligand (PD-L1) interaction negatively regulates T cell function in head and neck squamous cell carcinoma (HNSCC). Overexpression of PD-1 reduces intracellular Ca2+ fluxes, and thereby T cell effector functions. In HNSCC patients, PD-1 blockade increases KCa3.1 and Kv1.3 activity along with Ca2+ signaling and mobility in CD8+ peripheral blood T cells (PBTs). The mechanism by which PD-L1/PD-1 interaction regulates ion channel function is not known. We investigated the effects of blocking PD-1 and PD-L1 on ion channel functions and intracellular Ca2+ signaling in CD8+ PBTs of HNSCC patients and healthy donors (HDs) using single-cell electrophysiology and live microscopy. Anti-PD-1 and anti-PD-L1 antibodies increase KCa3.1 and Kv1.3 function in CD8+ PBTs of HNSCC patients. Anti-PD-1 treatment increases Ca2+ fluxes in a subset of HSNCC patients. In CD8+ PBTs of HDs, exposure to PD-L1 reduces KCa3.1 activity and Ca2+ signaling, which were restored by anti-PD-1 treatment. The PD-L1-induced inhibition of KCa3.1 channels was rescued by the intracellular application of the PI3 kinase modulator phosphatidylinositol 3-phosphate (PI3P) in patch-clamp experiments. In HNSCC CD8+ PBTs, anti-PD-1 treatment did not affect the expression of KCa3.1, Kv1.3, Ca2+ release activated Ca2+ (CRAC) channels, and markers of cell activation (CD69) and exhaustion (LAG-3 and TIM-3). Our data show that immune checkpoint blockade improves T cell function by increasing KCa3.1 and Kv1.3 channel activity in HNSCC patients.

scholarly journals Distinct roles of the last transmembrane domain in controlling Arabidopsis K+ channel activity

2009 ◽  
Vol 182 (2) ◽  
pp. 380-391 ◽  
Author(s):  
Pawel Gajdanowicz ◽  
Carlos Garcia-Mata ◽  
Wendy Gonzalez ◽  
Samuel Elías Morales-Navarro ◽  
Tripti Sharma ◽  
...  
Keyword(s):  
Transmembrane Domain ◽  
K Channel ◽  
Channel Activity

scholarly journals Single Streptomyces lividans K+ Channels

1999 ◽  
Vol 114 (4) ◽  
pp. 551-560 ◽  
Author(s):  
Lise Heginbotham ◽  
Meredith LeMasurier ◽  
Ludmilla Kolmakova-Partensky ◽  
Christopher Miller
Keyword(s):  
Open Channel ◽  
Low Ph ◽  
K Channel ◽  
Channel Activity ◽  
Lipid Bilayer Membranes ◽  
Bilayer Membranes ◽  
Electrophysiological Properties ◽  
Channel Current ◽  
Side Channels ◽  
Voltage Dependent

Basic electrophysiological properties of the KcsA K+ channel were examined in planar lipid bilayer membranes. The channel displays open-state rectification and weakly voltage-dependent gating. Tetraethylammonium blocking affinity depends on the side of the bilayer to which the blocker is added. Addition of Na+ to the trans chamber causes block of open-channel current, while addition to the cis side has no effect. Most striking is the activation of KcsA by protons; channel activity is observed only when the trans bilayer chamber is at low pH. To ascertain which side of the channel faces which chamber, residues with structurally known locations were mapped to defined sides of the bilayer. Mutation of Y82, an external residue, results in changes in tetraethylammonium affinity exclusively from the cis side. Channels with cysteine residues substituted at externally exposed Y82 or internally exposed Q119 are functionally modified by methanethiosulfonate reagents from the cis or trans chambers, respectively. Block by charybdotoxin, known to bind to the channel's external mouth, is observed only when the toxin is added to the cis side of channels mutated to be toxin sensitive. These results demonstrate unambiguously that the protonation sites linked to gating are on the intracellular portion of the KcsA protein.

scholarly journals Molecular Analysis of ATP-sensitive K Channel Gating and Implications for Channel Inhibition by ATP

1998 ◽  
Vol 112 (3) ◽  
pp. 333-349 ◽  
Author(s):  
Stefan Trapp ◽  
Peter Proks ◽  
Stephen J. Tucker ◽  
Frances M. Ashcroft
Keyword(s):  
Transmembrane Domain ◽  
K Channel ◽  
Channel Activity ◽  
Inhibitory Effects ◽  
Open Probability ◽  
Regulatory Subunits ◽  
Closed State ◽  
Channel Inhibition ◽  
Apparent Decrease ◽  
Atp Inhibition

The β cell KATP channel is an octameric complex of four pore-forming subunits (Kir6.2) and four regulatory subunits (SUR1). A truncated isoform of Kir6.2 (Kir6.2ΔC26), which expresses independently of SUR1, shows intrinsic ATP sensitivity, suggesting that this subunit is primarily responsible for mediating ATP inhibition. We show here that mutation of C166, which lies at the cytosolic end of the second transmembrane domain, to serine (C166S) increases the open probability of Kir6.2ΔC26 approximately sevenfold by reducing the time the channel spends in a long closed state. Rundown of channel activity is also decreased. Kir6.2ΔC26 containing the C166S mutation shows a markedly reduced ATP sensitivity: the Ki is reduced from 175 μM to 2.8 mM. Substitution of threonine, alanine, methionine, or phenylalanine at position C166 also reduced the channel sensitivity to ATP and simultaneously increased the open probability. Thus, ATP does not act as an open channel blocker. The inhibitory effects of tolbutamide are reduced in channels composed of SUR1 and Kir6.2 carrying the C166S mutation. Our results are consistent with the idea that C166 plays a role in the intrinsic gating of the channel, possibly by influencing a gate located at the intracellular end of the pore. Kinetic analysis suggests that the apparent decrease in ATP sensitivity, and the changes in other properties, observed when C166 is mutated is largely a consequence of the impaired transition from the open to the long closed state.

scholarly journals Localization and targeting of the Saccharomyces cerevisiae Kre2p/Mnt1p alpha 1,2-mannosyltransferase to a medial-Golgi compartment.

1995 ◽  
Vol 131 (4) ◽  
pp. 913-927 ◽  
Author(s):  
M Lussier ◽  
A M Sdicu ◽  
T Ketela ◽  
H Bussey
Keyword(s):  
Membrane Protein ◽  
Transmembrane Domain ◽  
Glycosylation Site ◽  
Dependent Manner ◽  
Reporter Protein ◽  
Golgi Localization ◽  
Golgi Compartment ◽  
Membrane Spanning

The yeast Kre2p/Mnt1p alpha 1,2-mannosyltransferase is a type II membrane protein with a short cytoplasmic amino terminus, a membrane-spanning region, and a large catalytic luminal domain containing one N-glycosylation site. Anti-Kre2p/Mnt1p antibodies identify a 60-kD integral membrane protein that is progressively N-glycosylated in an MNN1-dependent manner. Kre2p/Mnt1p is localized in a Golgi compartment that overlaps with that containing the medial-Golgi mannosyltransferase Mnn1p, and distinct from that including the late Golgi protein Kex1p. To determine which regions of Kre2p/Mnt1p are required for Golgi localization, Kre2p/Mnt1p mutant proteins were assembled by substitution of Kre2p domains with equivalent sequences from the vacuolar proteins DPAP B and Pho8p. Chimeric proteins were tested for correct topology, in vitro and in vivo activity, and were localized intracellularly by indirect immunofluorescence. The results demonstrate that the NH2-terminal cytoplasmic domain is necessary for correct Kre2p Golgi localization whereas, the membrane-spanning and stem domains are dispensable. However, in a test of targeting sufficiency, the presence of the entire Kre2p cytoplasmic tail, plus the transmembrane domain and a 36-amino acid residue luminal stem region was required to localize a Pho8p reporter protein to the yeast Golgi.

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