Stochastic Gating as a Novel Mechanism for Channel Selectivity

An ideal channel, responsible for metabolite fluxes in and out of the cells and cellular compartments, is supposed to be selective for a particular set of molecules only. However, such a channel has to be wide enough to accommodate relatively large metabolites, and, therefore, it allows passage of smaller solutes, for example, sodium, potassium, and chloride ions, thus compromising membrane’s barrier function. Here we show that stochastic gating is able to provide a mechanism for the selectivity of wide channels in favor of large metabolites. Specifically, applying our recent theory of the stochastic gating effect on channel-facilitated transport, we demonstrate that under certain conditions gating hinders translocation of fast-diffusing small solutes to a significantly higher degree than that of large solutes that diffuse much slower. We hypothesize that this can be used by Nature to minimize the shunting effect of wide channels with respect to small solutes.     

Nonlamellar-Phase-Promoting Colipids Enhance Segregation of Palmitoyl Ceramide in Fluid Bilayers

Ceramide is an important intermediate in sphingolipid homeostasis. We examined how colipids, with negative intrinsic curvature and which may induce curvature stress in the bilayers, affected the segregation of palmitoyl ceramide (PCer). Such colipids include 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and tetra-linoleoyl cardiolipin (CL). In 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers, PCer formed ordered, gel-like domains at concentrations above 10 mol% at 23°C, as evidenced by the change in the average lifetime of the trans-parinaric acid emission. When POPE or DOPE were included in the DOPC bilayer (at 20:80 or 40:60 POPE or DOPE to DOPC, by mol), the lateral segregation of PCer was facilitated in a concentration-dependent manner, and less PCer was required for the formation of the ordered ceramide-rich domains. Inclusion of CL in the DOPE bilayer (at 10:90 or 20:80 CL to PC, by mol) also caused a similar facilitation of the lateral segregation of PCer. The PCer-rich domains formed in the presence of POPE, DOPE, or CL in DOPC bilayers were slightly more thermostable (by 2–10°C) when compared to PCer-rich domains in DOPC-only bilayers. Nonlamellar phases were not present in bilayers in which the effects of POPE or DOPE on PCer segregation were the largest, as verified by ³¹P NMR. When palmitoyl sphingomyelin was added to the different bilayer compositions at 5 mol%, relative to the phospholipids, PCer segregated into gel domains at lower concentrations (2–3 mol% PCer), and the effect of POPE on PCer segregation was eliminated. We suggest that the effects of POPE, DOPE, and CL on PCer segregation was in part influenced by their effects on membrane curvature stress and in part because of unfavorable interactions with PCer due to their unsaturated acyl chains. These lipids are abundant in mitochondrial membranes and are likely to affect functional properties of saturated ceramides in them.     

A Dense Starburst Plexus Is Critical for Generating Direction Selectivity

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The Antiparallel Dimerization of Myosin X Imparts Bundle Selectivity for Processive Motility

Myosin X is an unconventional actin-based molecular motor involved in filopodial formation, microtubule-actin filament interaction, and cell migration. Myosin X is an important component of filopodia regulation, localizing to tips of growing filopodia by an unclear targeting mechanism. The native α-helical dimerization domain of myosin X is thought to associate with antiparallel polarity of the two amino acid chains, making myosin X the only myosin that is currently considered to form antiparallel dimers. This study aims to determine if antiparallel dimerization of myosin X imparts selectivity toward actin bundles by comparing the motility of parallel and antiparallel dimers of myosin X on single and fascin-bundled actin filaments. Antiparallel myosin X dimers exhibit selective processivity on fascin-bundled actin and are only weakly processive on single actin filaments below saturating [ATP]. Artificial forced parallel dimers of myosin X are robustly processive on both single and bundled actin, exhibiting no selectivity. To determine the relationship between gating of the reaction steps and observed differences in motility, a mathematical model was developed to correlate the parameters of motility with the biochemical and mechanical kinetics of the dimer. Results from the model, constrained by experimental data, suggest that the probability of binding forward, toward the barbed end of the actin filament, is lower in antiparallel myosin X on single actin filaments compared to fascin-actin bundles and compared to constructs of myosin X with parallel dimerization.     

Selectivity of different biological products to the egg parasitoid Telenomus remus (Hymenoptera: Platygastridae)

The selectivity of five entomopathogens and a chemical insecticide (positive control) to pupae and adults of the egg parasitoid Telenomus remus (Nixon) was evaluated in the laboratory under controlled environmental conditions according to protocols established by the International Organization for Biological Control. Baculovirus anticarsia (Baculovirus AEE^®), Bacillus thuringiensis var. kurstaki (Thuricide^®), Bacillus thuringiensis var. aizawai (Agree^®), Beauveria bassiana (Boveril^®), Metarhizium anisopliae (Metarril^®) and Trichoderma harzianum (Trichodermil^®) are harmless to T. remus pupae, and adults. Thus, our results suggest that the insect control strategies applied here are compatible since entomopathogens were classified as harmless to T. remus in most examined cases and therefore facilitate a joint application to control different pests. Bacillus thuringiensis var. kurstaki (Dipel^®), despite being classified as slightly harmful in some of the evaluations, can still be considered compatible for use together with T. remus, especially when compared with chemical insecticides such as chlorpyrifos that might be considered harmful to the parasitoid survival.     

Vesicular GABA Uptake Can Be Rate Limiting for Recovery of IPSCs from Synaptic Depression

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