Search for monotop signatures in proton-proton collisions at √s=8 TeV

Results are presented from a search for new decaying massive particles whose presence is inferred from an imbalance in transverse momentum and which are produced in association with a single top quark that decays into a bottom quark and two light quarks. The measurement is performed using 19.7  fb^{-1} of data from proton-proton collisions at a center-of-mass energy of 8 TeV, collected with the CMS detector at the CERN LHC. No deviations from the standard model predictions are observed and lower limits are set on the masses of new invisible bosons. In particular, scalar and vector particles, with masses below 330 and 650 GeV, respectively, are excluded at 95% confidence level, thereby substantially extending a previous limit published by the CDF Collaboration.

Search for a dark matter candidate produced in association with a single top quark in pp collisions at √[s]=1.96 TeV

We report a new search for dark matter in a data sample of an integrated luminosity of 7.7  fb-1 of Tevatron pp[over ¯] collisions at √[s]=1.96  TeV, collected by the CDF II detector. We search for production of a dark-matter candidate, D, in association with a single top quark. We consider the hadronic decay mode of the top quark exclusively, yielding a final state of three jets with missing transverse energy. The data are consistent with the standard model; we thus set 95% confidence level upper limits on the cross section of the process pp[over ¯]→t+D as a function of the mass of the dark-matter candidate. The limits are approximately 0.5 pb for a dark-matter particle with mass in the range of 0-150  GeV/c2.

Solubilization and immunopurification of rat brain synaptic vesicle protein 2A with maintained binding properties

This study reports the solubilization of the rat synaptic vesicle protein SV2A, the brain binding site for the antiepileptic drug levetiracetam (LEV), and its characterization. N-dodecyl-beta-D-maltoside (DDM) was the best detergent at achieving a high percentage of SV2A solubilization and at maintaining the binding characteristics of a tritiated form of a more potent analogue of LEV, [3H]ucb 30889 ((2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide). Scatchard analysis revealed that approximately 25% of SV2A proteins from brain membranes are solubilized by DDM under optimal conditions. Competition binding experiments with a variety of LEV analogues indicated that [3H]ucb 30889 labels the same binding site in both crude homogenates and soluble extracts, with still high stereoselectivity. After immunoprecipitation of SV2A from solubilized rat brain membranes, binding properties of [3H]ucb 30889 to SV2A and association with synaptotagmin I were maintained. The two other isoforms SV2B and SV2C were found to be co-immunoprecipitated with SV2A. The solubilization and immunopurification of SV2A with unmodified ligand affinities and synaptotagmin I interaction provides the starting point for future protein-protein interactions and structural studies.

Failure of GPI compounds to display neurotrophic activity in vitro and in vivo

The aim of this study was to evaluate the neurotrophic and neuroprotective properties of a series of immunophilin ligands and to assess the potential involvement of FK506 Binding Protein 12 kDa (FKBP12) rotamase inhibition in this activity. Both FK506 and rapamycin induced a potent inhibition of the FKBP12 rotamase activity (pIC(50) values of 7.3 and 7.4, respectively) but only a modest inhibition was observed with 1-(3,3-dimethyl-2-oxo-pentanoyl)-pyrrolidine-2-carboxylic acid S-3-pyridin-3-yl-propyl ester (GPI 1046) (5.8), its N-oxide (5.4) and thioester (6.3) analogues. Compared to nerve growth factor, all these immunophilin ligands only induced marginal increases in neurite outgrowth of rat dissociated newborn dorsal root ganglia cells. Furthermore, systemic administration of GPI 1046 and its N-oxide and thioester analogues failed to prevent striatal dopamine depletion induced by acute or chronic i.p. treatment with 1-methyl-4-phenyl 1,2,3,6 tetrahydropyridine (MPTP). These results suggest that inhibition of FKBP12 rotamase activity is not predictive for neurotrophic and neuroprotective properties of immunophilin ligands and question their therapeutic utility in neurodegenerative diseases like Parkinson's disease.

Lentil seed aquaporins form a hetero-oligomer which is phosphorylated by a Mg(2+)-dependent and Ca(2+)-regulated kinase

In plants, aquaporins regulate the water flow through membranes during growth, development and stress responses. We have isolated two isoforms of the aquaporin family from the protein-storage vacuoles of lentil (Lens culinaris Med.) seeds. Chemical cross-linking experiments showed that both isoforms belong to the same oligomer in the membrane and are phosphorylated by a membrane-bound protein kinase. We assigned the kinase activity to a 52 kDa protein that is magnesium-dependent and calcium-regulated.

Passive anion transport through the chloroplast inner envelope membrane measured by osmotic swelling of intact chloroplasts

It has been shown that chloride channels are located in the envelope membranes of chloroplasts [5,11]. In this report, we use the light-scattering technique to measure quantitatively the rate of anion transport through the inner envelope membrane of isolated intact chloroplasts. Our results permit to assign the anion transport to the inner envelope of chloroplasts. The anionic selectivity determined from the kinetics of light scattering indicates that the chloride pathway is also highly permeable for NO-2 and NO-3. The sulfate and phosphate anions are impermeant. The chloride flux is not inhibited by DIDS or NEM and is temperature-dependent. The activation energy of the transport process suggests that the Cl- flux occurs through a channel.

Tic20 and Tic22 are new components of the protein import apparatus at the chloroplast inner envelope membrane

Two components of the chloroplast envelope, Tic20 and Tic22, were previously identified as candidates for components of the general protein import machinery by their ability to covalently cross-link to nuclear-encoded preproteins trapped at an intermediate stage in import across the envelope (Kouranov, A., and D.J. Schnell. 1997. J. Cell Biol. 139:1677-1685). We have determined the primary structures of Tic20 and Tic22 and investigated their localization and association within the chloroplast envelope. Tic20 is a 20-kD integral membrane component of the inner envelope membrane. In contrast, Tic22 is a 22-kD protein that is located in the intermembrane space between the outer and inner envelope membranes and is peripherally associated with the outer face of the inner membrane. Tic20, Tic22, and a third inner membrane import component, Tic110, associate with import components of the outer envelope membrane. Preprotein import intermediates quantitatively associate with this outer/inner membrane supercomplex, providing evidence that the complex corresponds to envelope contact sites that mediate direct transport of preproteins from the cytoplasm to the stromal compartment. On the basis of these results, we propose that Tic20 and Tic22 are core components of the protein translocon of the inner envelope membrane of chloroplasts.

Mechanism of proton permeation through chloroplast lipid membranes

Electrical measurements were carried out to investigate the contribution of chloroplast lipids to the passive proton permeability of both the thylakoid and inner-envelope membranes. Permeability coefficient and conductance to protons were measured for solvent-free bilayers made from monogalactosyldiglyceride:digalactosyldiglycerid: sulfoquinovosyldiglyceride:phosphatidylglycerol (2:1:0.5:0.5, w/w) in the presence of a pH gradient of 7.4/8.1. The permeability coefficient for protons in glycolipids was 5.5 +/- 1.1 x 10(-4) cm s-1 (n = 14). To determine whether this high H+ permeability could be explained by the presence of lipid contaminants such as weak acids, we investigated the effects of (a) bovine serum albumin, which can remove some amphiphilic molecules such as free fatty acids, (b) 6-ketocholestanol, which increases the membrane dipole potential, (c) oleic acid, and (d) chlorodecane, which increases the dielectric constant of the lipid bilayer. Our results show that free fatty acids are inefficient protonophores, as compared with carbonylcyanide-m-chlorphenythydrazone, and that the hypothesis of a weak acid mechanism is not valid with glycolipid bilayers. In the presence of deuterium oxide the H+ conductane was reduced significantly, indicating that proton transport through the glycolipid matrix could occur directly by a hydrogen bond process. The passive transport of H+ through the glycolipid matrix is discussed with regard to the activity of the thylakoid ATP synthase and the inner-envelope H(+)-ATPase.

A voltage-dependent porin-like channel in the inner envelope membrane of plant chloroplasts

The electrical activity of a single channel of 525 +/- 12 picosiemens in 150 mM KCl was measured after fusion of the inner envelope membrane of the chloroplast with planar lipid bilayers. The reversal potentials measured in KCl gradients indicate that this channel is weakly anion selective (PCl/PK = 1.6 +/- 0.2). The gating mechanism of the pore is voltage dependent. The channel shifts from a fully open state to a substrate at positive electrical potentials and remains closed at negative electrical potentials. Succinylation of the protein increases the open probability of the fully open state and reverses the channel selectivity. Analysis of the single-channel conductance as a function of the salt concentration and of the open probability at various voltages suggests that this channel is a new membrane porin not previously identified.

Permeability and electrical properties of planar lipid membranes from thylakoid lipids

Electrical measurements were carried out on planar lipid membranes from thylakoid lipids. The specific capacitance of membranes formed from decane-containing monogalactosyldiacylglycerol (MGDG), which accounts for 57% of the total lipid content of thylakoids, showed that it adopted a bilayer structure. Solvent-free bilayers of MGDG were not formed, with very rare exceptions, indicating that decane is required to stabilize the planar conformation. However, this cone-shaped lipid produces bilayer structures in combination with other cylindrical thylakoid lipids even in the absence of organic solvent. We compared the properties of solvent-free and decane-containing bilayers from MGDG, soybean lecithin, and the quaternary mixture of lipids similar to that found in vivo. The conductance of decane-MGDG was 26 times higher than that of decane-lecithin. The flux through the decane-lecithin bilayer was found to be slightly dependent on pH, whereas the decane-MGDG membrane was not. The specific conductance of bilayers formed from the quaternary mixture of lipids was 5 to 10 times larger than lecithin (with alkane or not). Further experiments with bilayers made in the presence of a KCl gradient showed that decane-MGDG, decane-MGDG/DGDG/SQDG/PG, and solvent-free MGDG/DGDG/SQDG/PG were cation-selective. The permeability coefficient for potassium ranged from 4.9 to 8.3 x 10(-11) cm s-1. The permeability coefficient for protons in galactolipids, however, was determined to be about six orders of magnitude higher than the value for potassium ions. The HCl permeation mechanism through the lipid membranes was determined from diffusion potentials measured in HCl gradients. Our results suggest that HCl was not transported as neutral molecules. The data is discussed with regard to the function of galactolipids in the ion transport through thylakoid membranes.