Search results for " channels."
showing 10 items of 386 documents
Canonical azimuthal rotations and flanking residues constrain the orientation of transmembrane helices.
2013
AbstractIn biological membranes the alignment of embedded proteins provides crucial structural information. The transmembrane (TM) parts have well-defined secondary structures, in most cases α-helices and their orientation is given by a tilt angle and an azimuthal rotation angle around the main axis. The tilt angle is readily visualized and has been found to be functionally relevant. However, there exist no general concepts on the corresponding azimuthal rotation. Here, we show that TM helices prefer discrete rotation angles. They arise from a combination of intrinsic properties of the helix geometry plus the influence of the position and type of flanking residues at both ends of the hydrop…
Functional competition within a membrane: Lipid recognition vs. transmembrane helix oligomerization
2015
Abstract Binding of specific lipids to large, polytopic membrane proteins is well described, and it is clear that such lipids are crucial for protein stability and activity. In contrast, binding of defined lipid species to individual transmembrane helices and regulation of transmembrane helix monomer–oligomer equilibria by binding of distinct lipids is a concept, which has emerged only lately. Lipids bind to single-span membrane proteins, both in the juxta-membrane region as well as in the hydrophobic membrane core. While some interactions counteract transmembrane helix oligomerization, in other cases lipid binding appears to enhance oligomerization. As reversible oligomerization is involve…
Molecular and topological membrane folding determinants of transient receptor potential vanilloid 2 channel.
2015
Transient Receptor Potential (TRP) channels are related to adaptation to the environment and somatosensation. The transient receptor potential vanilloid (TRPV) subfamily includes six closely evolutionary related ion channels sharing the same domain organization and tetrameric arrangement in the membrane. In this study we have characterized biochemically TRPV2 channel membrane protein folding and transmembrane (TM) architecture. Deleting the first N-terminal 74 residues preceding the ankyrin repeat domain (ARD) show a key role for this region in targeting the protein to the membrane. We have demonstrated the co-translational insertion of the membrane-embedded region of the TRPV2 and its disp…
Cluster organization and pore structure of ion channels formed by beticolin 3, a nonpeptidic fungal toxin
1999
Beticolin 3 (B3) belongs to a family of nonpeptidic phytotoxins produced by the fungus Cercospora beticola, which present a broad spectrum of cytotoxic effects. We report here that, at cytotoxic concentration (10 microM), B3 formed voltage-independent, weakly selective ion channels with multiple conductance levels in planar lipid bilayers. In symmetrical standard solutions, conductance values of the first levels were, respectively, 16 +/- 1 pS, 32 +/- 2 pS, and 57 +/- 2 pS (n = 4) and so on, any conductance level being roughly twice the lower one. Whether a cluster organization of elementary channels or different channel structures underlies this particular property was addressed by investi…
Solution structure of aD,L-alternating oligonorleucine as a model of double-stranded antiparallel ?-helix
2002
Conformational characteristics of alternating D,L linear peptides are of particular interest because of their capacity to form transmembrane channels with different transport properties, as some natural antibiotics do. Single- and double-stranded beta-helical structures are common for alternating D,L peptides. The stability of the beta-helix depends on several structural factors, such as the backbone peptide length, type and position of side chains, and nature of terminal groups. The NMR and molecular dynamics solution conformation of a synthetic alternating D,L-oligopeptide with 15 norleucines (XVMe) has been used as a model to get insight in to the conformational features of double-strand…
Complement lysis: a hole is a hole.
1991
recent experimental advances 21, it is now possible to produce MACs with a precise molecular composition 7 for better designed experiments. In my judgement, however, it will always be problematic to propose a single unifying mechanism for MAC action simply because MAC effects are not uniform. The reason for attempting to classify MACs as leaky patch or channel formers is a desire to wield Occam's razor and carve out the simplest unifying theory. But this razor often cuts one's throat, especially when it comes to immunological processes. A system that degranulates platelets, 'kills' such widely diverse targets as artificial liposomes, 'dead' viruses and erythrocytes, metabolically active cel…
Identification of Synaptic Integration Mode in CA3 Pyramidal Neuron Model
2019
International audience; A morphologically realistic and anisotropic model of CA3 pyramidal neuron was developed to determine the synaptic integration modes the neuron is able to perform. Linearity and nonlinearity were identified in different synaptic locations with varying active mechanisms such as the presence of ionic channels in the dendritic arbor and the types of receptors in the synapse. Quantification of synaptic integration was performed using paired-pulse stimulation protocol and subthreshold input/output (sI/O) transformation. Results show that the mode of synaptic integration is location-dependent while the linearity or nonlinearity in the integration is mainly influenced by the…
Putative excitatory and putative inhibitory inputs are localised in different dendritic domains in aDrosophilaflight motoneuron
2012
Input-output computations of individual neurons may be affected by the three-dimensional structure of their dendrites and by the targeting of input synapses to specific parts of their dendrites. However, only few examples exist where dendritic architecture can be related to behaviorally relevant computations of a neuron. By combining genetic, immunohistochemical, and confocal laser scanning methods this study estimates the location of the spike initiating zone and the dendritic distribution patterns of putative synaptic inputs on an individually identified Drosophila flight motorneuron, MN5. MN5 is a monopolar neuron with more than 4000 dendritic branches. The site of spike initiation was e…
Killer-toxin-resistant kre12 mutants of Saccharomyces cerevisiae: genetic and biochemical evidence for a secondary K1 membrane receptor.
1995
The Saccharomyces cerevisiae killer toxin K1 is a secreted alpha/beta-heterodimeric protein toxin that kills sensitive yeast cells in a receptor-mediated two-stage process. The first step involves toxin binding to beta-1,6-D-glucan-components of the outer yeast cell surface; this step is blocked in yeast mutants bearing nuclear mutations in any of the KRE genes whose products are involved in synthesis and/or assembly of cell wall beta-D-glucans. After binding to the yeast cell wall, the killer toxin is transferred to the cytoplasmic membrane, subsequently leading to cell death by forming lethal ion channels. In an attempt to identify a secondary K1 toxin receptor at the plasma membrane leve…
Current rectification by nanoparticle blocking in single cylindrical nanopores.
2014
Blocking of a charged pore by an oppositely charged nanoparticle can support rectifying properties in a cylindrical nanopore, as opposed to the usual case of a fixed asymmetry in the pore geometry and charge distribution. We present here experimental data and model calculations to confirm this fundamental effect. The nanostructure imaging and the effects of nanoparticle concentration, pore radius, and salt concentration on the electrical conductance–voltage (G–V) curves are discussed. Logic responses based on chemical and electrical inputs/outputs could also be implemented with a single pore acting as an effective nanofluidic diode. To better show the generality of the results, different ch…