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1.
Voltage-dependent potassium ion (K+) channels (Kv channels) conduct K+ ions across the cell membrane in response to changes in the membrane voltage, thereby regulating neuronal excitability by modulating the shape and frequency of action potentials. Here we report the crystal structure, at a resolution of 2.9 angstroms, of a mammalian Kv channel, Kv1.2, which is a member of the Shaker K+ channel family. This structure is in complex with an oxido-reductase beta subunit of the kind that can regulate mammalian Kv channels in their native cell environment. The activation gate of the pore is open. Large side portals communicate between the pore and the cytoplasm. Electrostatic properties of the side portals and positions of the T1 domain and beta subunit are consistent with electrophysiological studies of inactivation gating and with the possibility of K+ channel regulation by the beta subunit. 相似文献
2.
The mechanosensitive channel of small conductance (MscS) responds both to stretching of the cell membrane and to membrane depolarization. The crystal structure at 3.9 angstroms resolution demonstrates that Escherichia coli MscS folds as a membrane-spanning heptamer with a large cytoplasmic region. Each subunit contains three transmembrane helices (TM1, -2, and -3), with the TM3 helices lining the pore, while TM1 and TM2, with membrane-embedded arginines, are likely candidates for the tension and voltage sensors. The transmembrane pore, apparently captured in an open state, connects to a large chamber, formed within the cytoplasmic region, that connects to the cytoplasm through openings that may function as molecular filters. Although MscS is likely to be structurally distinct from other ion channels, similarities in gating mechanisms suggest common structural elements. 相似文献
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4.
Sequence and expression of mRNAs encoding the alpha 1 and alpha 2 subunits of a DHP-sensitive calcium channel 总被引：23，自引：0，他引：23
S B Ellis M E Williams N R Ways R Brenner A H Sharp A T Leung K P Campbell E McKenna W J Koch A Hui 《Science (New York, N.Y.)》1988,241(4873):1661-1664
Complementary DNAs were isolated and used to deduce the primary structures of the alpha 1 and alpha 2 subunits of the dihydropyridine-sensitive, voltage-dependent calcium channel from rabbit skeletal muscle. The alpha 1 subunit, which contains putative binding sites for calcium antagonists, is a hydrophobic protein with a sequence that is consistent with multiple transmembrane domains and shows structural and sequence homology with other voltage-dependent ion channels. In contrast, the alpha 2 subunit is a hydrophilic protein without homology to other known protein sequences. Nucleic acid hybridization studies suggest that the alpha 1 and alpha 2 subunit mRNAs are expressed differentially in a tissue-specific manner and that there is a family of genes encoding additional calcium channel subtypes. 相似文献
5.
Voltage-dependent ion channels contain voltage sensors that allow them to switch between nonconductive and conductive states over the narrow range of a few hundredths of a volt. We investigated the mechanism by which these channels sense cell membrane voltage by determining the x-ray crystal structure of a mammalian Shaker family potassium ion (K+) channel. The voltage-dependent K+ channel Kv1.2 grew three-dimensional crystals, with an internal arrangement that left the voltage sensors in an apparently native conformation, allowing us to reach three important conclusions. First, the voltage sensors are essentially independent domains inside the membrane. Second, they perform mechanical work on the pore through the S4-S5 linker helices, which are positioned to constrict or dilate the S6 inner helices of the pore. Third, in the open conformation, two of the four conserved Arg residues on S4 are on a lipid-facing surface and two are buried in the voltage sensor. The structure offers a simple picture of how membrane voltage influences the open probability of the channel. 相似文献
6.
Nuclear pore complexes are multiprotein channels that span the double lipid bilayer of the nuclear envelope. How new pores are inserted into the intact nuclear envelope of proliferating and differentiating eukaryotic cells is unknown. We found that the Nup107-160 complex was incorporated into assembly sites in the nuclear envelope from both the nucleoplasmic and the cytoplasmic sides. Nuclear pore insertion required the generation of Ran guanosine triphosphate in the nuclear and cytoplasmic compartments. Newly formed nuclear pore complexes did not contain structural components of preexisting pores, suggesting that they can form de novo. 相似文献
7.
Evidence that the M2 membrane-spanning region lines the ion channel pore of the nicotinic receptor 总被引：29，自引：0，他引：29
R J Leonard C G Labarca P Charnet N Davidson H A Lester 《Science (New York, N.Y.)》1988,242(4885):1578-1581
Site-directed mutagenesis and expression in Xenopus oocytes were used to study acetylcholine receptors in which serine residues (i) were replaced by alanines (alpha, delta subunits) or (ii) replaced a phenylalanine (beta subunit) at a postulated polar site within the M2 transmembrane helix. As the number of serines decreased, there were decreases in the residence time and consequently the equilibrium binding affinity of QX-222, a quaternary ammonium anesthetic derivative thought to bind within the open channel. Receptors with three serine-to-alanine mutations also displayed a selective decrease in outward single-channel currents. Both the direction of this rectification and the voltage dependence of QX-222 blockade suggest that the residues mutated are within the aqueous pore of the receptor and near its cytoplasmic (inner) surface. 相似文献
8.
Tadokoro S Shattil SJ Eto K Tai V Liddington RC de Pereda JM Ginsberg MH Calderwood DA 《Science (New York, N.Y.)》2003,302(5642):103-106
Control of integrin affinity for ligands (integrin activation) is essential for normal cell adhesion, migration, and assembly of an extracellular matrix. Integrin activation is usually mediated through the integrin beta subunit cytoplasmic tail and can be regulated by many different biochemical signaling pathways. We report that specific binding of the cytoskeletal protein talin to integrin beta subunit cytoplasmic tails leads to the conformational rearrangements of integrin extracellular domains that increase their affinity. Thus, regulated binding of talin to integrin beta tails is a final common element of cellular signaling cascades that control integrin activation. 相似文献
9.
Restoration of inactivation in mutants of Shaker potassium channels by a peptide derived from ShB 总被引：51，自引：0，他引：51
Site-directed mutagenesis experiments have suggested a model for the inactivation mechanism of Shaker potassium channels from Drosophila melanogaster. In this model, the first 20 amino acids form a cytoplasmic domain that interacts with the open channel to cause inactivation. The model was tested by the internal application of a synthetic peptide, with the sequence of the first 20 residues of the ShB alternatively spliced variant, to noninactivating mutant channels expressed in Xenopus oocytes. The peptide restored inactivation in a concentration-dependent manner. Like normal inactivation, peptide-induced inactivation was not noticeably voltage-dependent. Trypsin-treated peptide and peptides with sequences derived from the first 20 residues of noninactivating mutants did not restore inactivation. These results support the proposal that inactivation occurs by a cytoplasmic domain that occludes the ion-conducting pore of the channel. 相似文献
10.
The gramicidin pore: crystal structure of a cesium complex 总被引：15，自引：0，他引：15
Gramicidin, a linear polypeptide composed of hydrophobic amino acids with alternating L- and D- configurations, forms transmembrane ion channels. The crystal structure of a gramicidin-cesium complex has been determined at 2.0 angstrom resolution. In this structure, gramicidin forms a 26 angstrom long tube comprised of two polypeptide chains arranged as antiparallel beta strands that are wrapped into a left-handed helical coil with 6.4 residues per turn. The polypeptide backbone forms the interior of the hydrophilic, solvent-filled pore and the side chains form a hydrophobic and relatively regular surface on the outside of the pore. This example of a crystal structure of a solvent-filled ion pore provides a basis for understanding the physical nature of ion translocation. 相似文献
11.
Identification of an intracellular peptide segment involved in sodium channel inactivation 总被引：25，自引：0，他引：25
Antibodies directed against a conserved intracellular segment of the sodium channel alpha subunit slow the inactivation of sodium channels in rat muscle cells. Of four site-directed antibodies tested, only antibodies against the short intracellular segment between homologous transmembrane domains III and IV slowed inactivation, and their effects were blocked by the corresponding peptide antigen. No effects on the voltage dependence of sodium channel activation or of steady-state inactivation were observed, but the rate of onset of the antibody effect and the extent of slowing of inactivation were voltage-dependent. Antibody binding was more rapid at negative potentials, at which sodium channels are not inactivated; antibody-induced slowing of inactivation was greater during depolarizations to more positive membrane potentials. The peptide segment recognized by this antibody appears to participate directly in rapid sodium channel inactivation during large depolarizations and to undergo a conformational change that reduces its accessibility to antibodies as the channel inactivates. 相似文献
12.
Structure and function of voltage-sensitive ion channels 总被引：61，自引：0，他引：61
W A Catterall 《Science (New York, N.Y.)》1988,242(4875):50-61
Voltage-sensitive ion channels mediate action potentials in electrically excitable cells and play important roles in signal transduction in other cell types. In the past several years, their protein components have been identified, isolated, and restored to functional form in the purified state. Na+ and Ca2+ channels consist of a principal transmembrane subunit, which forms the ion-conducting pore and is expressed with a variable number of associated subunits in different cell types. The principal subunits of voltage-sensitive Na+, Ca2+, and K+ channels are homologous members of a gene family. Models relating the primary structures of these principal subunits to their functional properties have been proposed, and experimental results have begun to define a functional map of these proteins. Coordinated application of biochemical, biophysical, and molecular genetic methods should lead to a clear understanding of the molecular basis of electrical excitability. 相似文献
13.
为了鉴定F型与其他小麦雄性不育系细胞质类型之间差异。以F型不育系(FA1-1，FA1-2，FA2-1)、F型保持系、T、K、V型同核异质不育系(A)及其保持系（B）‘冀5418’等为试验材料，用23对叶绿体和21对线粒体SSR分子标记进行聚类分析。结果表明：FA与T、K、V、B型不育系的细胞质分属不同类别。FA与中国春(CS)的细胞质遗传相似系数为1.00，FA与FB细胞质遗传相似系数为1.00，表明其可能为普通小麦细胞质雄性不育系。与经典质核互作雄性不育原理有差异，F型雄性不育系的育性可能由核基因控制。 相似文献
14.
Heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) dissociate into guanosine triphosphate (GTP)-bound alpha subunits and a complex of beta and gamma subunits after interaction with receptors. The GTP-alpha subunit complex activates appropriate effectors, such as adenylyl cyclase, retinal phosphodiesterase, phospholipase C, and ion channels. G protein beta gamma subunits have been found to have regulatory effects on certain types of adenylyl cyclase. In the presence of Gs alpha, the alpha subunit of the G protein that activates adenylyl cyclase, one form of adenylyl cyclase was inhibited by beta gamma, some forms were activated by beta gamma, and some forms were not affected by beta gamma. These interactions suggest mechanisms for communication between distinct signal-transducing pathways. 相似文献
15.
T Scheuer V J Auld S Boyd J Offord R Dunn W A Catterall 《Science (New York, N.Y.)》1990,247(4944):854-858
Transfection of Chinese hamster ovary cells with complementary DNA encoding the RIIA sodium channel alpha subunit from rat brain led to expression of functional sodium channels with the rapid, voltage-dependent activation and inactivation characteristic of sodium channels in brain neurons. The sodium currents mediated by these transfected channels were inhibited by tetrodotoxin, persistently activated by veratridine, and prolonged by Leiurus alpha-scorpion toxin, indicating that neurotoxin receptor sites 1 through 3 were present in functional form. The RIIA sodium channel alpha subunit cDNA alone is sufficient for stable expression of functional sodium channels with the expected kinetic and pharmacological properties in mammalian somatic cells. 相似文献
16.
We have analyzed the local structure and dynamics of the prokaryotic voltage-dependent K+ channel (KvAP) at 0 millivolts, using site-directed spin labeling and electron paramagnetic resonance spectroscopy. We show that the S4 segment is located at the protein/lipid interface, with most of its charges protected from the lipid environment. Structurally, S4 is highly dynamic and is separated into two short helices by a flexible linker. Accessibility and dynamics data indicate that the S1 segment is surrounded by other parts of the protein. We propose that S1 is at the contact interface between the voltage-sensing and pore domains. These results establish the general principles of voltage-dependent channel structure in a biological membrane. 相似文献
17.
Transmembrane helical interactions and the assembly of the T cell receptor complex 总被引：23，自引：0，他引：23
Studies of the subunit interactions of the multicomponent T cell antigen receptor (TCR) revealed that specific pairs of chains have the ability to assemble after transfection into fibroblasts. For one such pair, TCR-alpha and CD3-delta, their ability to assemble was encoded by their transmembrane domains. The specificity of this interaction suggests that well-defined helical interactions in the membrane can explain the assembly of some multichain membrane complexes. 相似文献
18.
Ryanodine receptor of skeletal muscle is a gap junction-type channel 总被引：25，自引：0，他引：25
In the sarcoplasmic reticulum membrane of skeletal muscle, the ryanodine receptor forms an aqueous pore identified as the calcium-release pathway that operates during excitation-contraction coupling. The purified ryanodine receptor channel has now been shown to have four properties usually associated with gap junction channels: (i) a large nonspecific voltage-dependent conductance consisting of several open states; (ii) an inhibition of open probability by low pH; (iii) an inhibition of open probability by calcium; and (iv) a sensitivity to blockade by heptanol and octanol but not other alcohols. This functional homology may provide an insight into the mechanism of how muscle cells transduce depolarization into an intracellular release of calcium. 相似文献
19.
Altered K+ channel expression in abnormal T lymphocytes from mice with the lpr gene mutation 总被引：9，自引：0，他引：9
K G Chandy T E DeCoursey M Fischbach N Talal M D Cahalan S Gupta 《Science (New York, N.Y.)》1986,233(4769):1197-1200
The observation that voltage-dependent K+ channels are required for activation of human T lymphocytes suggests that pathological conditions involving abnormal mitogen responses might be reflected in ion channel abnormalities. Gigaohm seal techniques were used to study T cells from MRL/MpJ-lpr/lpr mice; these mice develop generalized lymphoproliferation of functionally and phenotypically abnormal T cells and a disease resembling human systemic lupus erythematosus. The number and predominant type of K+ channels in T cells from these mice differ dramatically from those in T cells from control strains and a congenic strain lacking the lpr gene locus. Thus an abnormal pattern of ion channel expression has now been associated with a genetic defect in cells of the immune system. 相似文献
20.
Micelles protect membrane complexes from solution to vacuum 总被引：1，自引：0，他引：1
The ability to maintain interactions between soluble protein subunits in the gas phase of a mass spectrometer gives critical insight into the stoichiometry and interaction networks of protein complexes. Conversely, for membrane protein complexes in micelles, the transition into the gas phase usually leads to the disruption of interactions, particularly between cytoplasmic and membrane subunits, and a mass spectrum dominated by large aggregates of detergent molecules. We show that by applying nanoelectrospray to a micellar solution of a membrane protein complex, the heteromeric adenosine 5'-triphosphate (ATP)-binding cassette transporter BtuC2D2, we can maintain the complex intact in the gas phase of a mass spectrometer. Dissociation of either transmembrane (BtuC) or cytoplasmic (BtuD) subunits uncovers modifications to the transmembrane subunits and cooperative binding of ATP. By protecting a membrane protein complex within a n-dodecyl-beta-d-maltoside micelle, we demonstrated a powerful strategy that will enable the subunit stoichiometry and ligand-binding properties of membrane complexes to be determined directly, by precise determination of the masses of intact complexes and dissociated subunits. 相似文献