26 research outputs found
Substrate binding accelerates the conformational transitions and substrate dissociation in multidrug efflux transporter AcrB
No full textThe tripartite efflux pump assembly AcrAB-TolC is the major multidrug resistance transporter in E. coli. The inner membrane transporter AcrB is a homotrimer, energized by the proton movement down the transmembrane electrochemical gradient. The asymmetric crystal structures of AcrB with three monomers in distinct conformational states (access (A), binding (B) and extrusion (E)) support a functional rotating mechanism, in which each monomer of AcrB cycles among the three states in a concerted way. However, the relationship between the conformational changes during functional rotation and drug translocation has not been totally understood. Here, we explored the conformational changes of the AcrB homotrimer during the ABE→BEA transition in different substrate-binding states using targeted MD simulations. It was found that the dissociation of substrate from the distal binding pocket of B monomer is closely related to the concerted conformational changes in the translocation pathway, especially the side chain reorientation of Phe628 and Tyr327. A second substrate binding at the proximal binding pocket of A monomer evidently accelerates the conformational transitions as well as substrate dissociation in B monomer. The acceleration effect of the multi-substrate binding mode provides a molecular explanation for the positive cooperativity observed in the kinetic studies of substrate efflux and deepens our understanding of the functional rotating mechanism of AcrB
Criteria for assessing the cooperative extension program planning process in the West central district of Virginia
No full textThe success of cooperative extension depends on the knowledge of how to apply the principles of extension education to situations where the activities are to be performed. The cooperative extension services dynamic localized approach to the solution of the common persons problem has stood the test of time. It is not necessary to establish a new system, but what is needed is to increase accountability and efficiency in the way programs are planned and developed.
The overall purpose of this study was to develop criteria for assessing the local cooperative extension program planning process in Virginia. Specific objectives that served as a basis for accomplishing the overall purpose of the study were:
1. To identify principles that are basic for planning an effective local extension program.
2. To verify these principles with a panel of experts.
3. To formulate criteria, based on the verified principles, to assess if on-going local extension programs were developed following the accepted programming principles.
4. To field test the criteria to determine the degree to which the criteria are used as guides during the local extension program planning process.
This study was a qualitative study. The principles identified and the criteria developed were reviewed by a panel of eight experts, then field tested in randomly selected extension units in the West Central Extension District of Virginia. Using personal interview methodology, unit directors of the randomly selected units were used for the field testing stage of this study.
Six of the seven principles identified as basic for planning/developing effective local extension programs were accepted by the panel of experts. Eighteen criteria were formulated based on the accepted principles. Criteria as used in this study implies an overall description of a set of related actions and/or operations which will be called standards of the planning process. It was found that most of the unit directors in the West-Central Extension District of Virginia interviewed for this study use the criteria as guides during their respective programming process. The panel of experts and unit directors agreed that the criteria were important as guides for local extension programming processes.
Based on the findings the author concluded that: (a) there are six essential principles for planning effective social extension programs; (b) that there are 18 criteria that can be used as guides for assessing if local extension programs are planned/developed using the essential extension program planning principles; and (c) that it is possible to assess local program planning activities in extension.
A recommendation made from the study that the process of assessing local program planning activities be tested statewide to increase the usability potential of the criteria and give possible directions for statewide in-service needs of unit directors and extension agents.Ed. D.incomplete_metadat
Negative modulation of NMDA receptor channel function by DREAM/calsenilin/KChIP3 provides neuroprotection?
No full textN-methyl D-aspartate receptors (NMDARs) are glutamate-gated ion channels highly permeable to calcium and essential to excitatory neurotransmission. The NMDARs have attracted much attention because of their role in synaptic plasticity and excitotoxicity. Evidence has recently accumulated that NMDARs are negatively regulated by intracellular calcium binding proteins. The calcium-dependent suppression of NMDAR function serves as a feedback mechanism capable of regulating subsequent Ca2+ entry into the postsynaptic cell, and may offer an alternative approach to treating NMDAR-mediated excitotoxic injury. This short review summarizes the recent progress made in understanding the negative modulation of NMDAR function by DREAM/calsenilin/KChIP3, a neuronal calcium sensor protein
Maternal separation produces alterations of forebrain brain-derived neurotrophic factor expression in differently aged rats
No full textEarly postnatal maternal separation (MS) can play an important role in the development of psychopathologies during ontogeny. In the present study, we investigated the effects of repeated MS (4 h per day from postnatal day [PND] 1–21) on the brain-derived neurotrophic factor (BDNF) expression in the medial prefrontal cortex (mPFC), the nucleus accumbens (NAc) and the hippocampus of male and female juvenile (PND 21), adolescent (PND 35) and young adult (PND 56) Wistar rats. The results indicated that MS increased BDNF in the CA1 and the dentate gyrus (DG) of adolescent rats as well as in the DG of young adult rats. However, the expression of BDNF in the mPFC in the young adult rats was decreased by MS. Additionally, in the hippocampus, there was decreased BDNF expression with age in both the MS and socially reared rats. However, in the mPFC, the BDNF expression was increased with age in the socially reared rats; nevertheless, the BDNF expression was significantly decreased in the MS young adult rats. In the NAc, the BDNF expression was increased with age in the male NMS rats, and the young adult female MS rats had less BDNF expression than the adolescent female MS rats. Th
Reg-2, a downstream signaling protein in the ciliary neurotrophic factor survival pathway, alleviates experimental autoimmune encephalomyelitis
No full textCiliary neurotrophic factor (CNTF), originally described as a neurocytokine that could support the survival of neurons, has been recently found to alleviate demyelination, prevent axon loss, and improve functional recovery in a rat model of acute experimental autoimmune encephalomyelitis (EAE). However, poor penetration into the brain parenchyma and unfavorable side effects limit the utility of CNTF. Here, we evaluated the therapeutic potential of a protein downstream of CNTF, regeneration gene protein 2 (Reg-2). Using multiple morphological, molecular biology, and electrophysiological methods to assess neuroinflammation, axonal loss, demyelination, and functional impairment, we observed that Reg-2 and CNTF exert similar effects in the acute phase of EAE. Both treatments attenuated axonal loss and demyelination, improved neuronal survival, and produced functional improvement. With a smaller molecular weight and improved penetration into the brain parenchyma, Reg-2 may be a useful substitute for CNTF therapy in EAE and multiple sclerosis
Genotypic variation in growth and physiological response to drought stress and re-watering reveals the critical role of recovery in drought adaptation in maize seedlings
No full textNon-irrigated crops in temperate climates and irrigated crops in arid climates are subjected to continuous cycles of water stress and re-watering. Thus, fast and efficient recovery from water stress may be among the key determinants of plant drought adaptation. The present study was designed to comparatively analyze the roles of drought resistance and drought recovery in drought adaptation and to investigate the physiological basis of genotypic variation in drought adaptation in maize (Zea mays) seedlings. As the seedlings behavior in growth associate with yield under drought, it could partly reflect the potential of drought adaptability. Growth and physiological responses to progressive drought stress and recovery were observed in seedlings of ten maize lines. The results showed that drought adaptability is closely related to drought recovery (r = 0.714**), but not to drought resistance (r = 0.332). Drought induced decreases in leaf water content, water potential, osmotic potential, gas exchange parameters, chlorophyll content, Fv/Fm and nitrogen content, and increased H2O2 accumulation and lipid peroxidation. After recovery, most of these physiological parameters rapidly returned to normal levels. The physiological responses varied between lines. Further correlation analysis indicated that the physiological bases of drought resistance and drought recovery are definitely different, and that maintaining higher chlorophyll content (r = 0.874***) and Fv/Fm (r = 0.626*) under drought stress contributes to drought recovery. Our results suggest that both drought resistance and recovery are key determinants of plant drought adaptation, and that drought recovery may play a more important role than previously thought. In addition, leaf water potential, chlorophyll content and Fv/Fm could be used as efficient reference indicators in the selection of drought-adaptive genotypes
Don't Always Prefer My Chosen Objects: Low Level of Trait Autonomy and Autonomy Deprivation Decreases Mere Choice Effect
No full textChoice effect is a robust phenomenon in which even mere choice that does not include actual choosing actions could result in more preference for the self-chosen objects over other-chosen objects. In the current research, we proposed that autonomy would impact the mere choice effect. We conducted two studies to examine the hypothesis. The results showed that the mere choice effect measured by Implicit Association Test (IAT) significantly decreased for participants with lower levels of trait autonomy (Study 1) and when participants were primed to experience autonomy deprivation (Study 2). The theoretical and practical implications are discussed
A High Throughput Assay for Screening Host Restriction Factors and Antivirals Targeting Influenza A Virus
No full textIInfluenza A virus (IAV) is a human respiratory pathogen that causes seasonal epidemics and occasional global pandemics with devastating levels of morbidity and mortality. Currently approved treatments against influenza are losing effectiveness as new viral strains are often refractory to conventional treatments. Thus, there is an urgent need to find new therapeutic targets with which to develop novel antiviral drugs. The common strategy to discover new drug targets and antivirals is high throughput screening. However, most current screenings for influenza A virus rely on the engineered virus carrying a reporter, which prevents the application to newly emerging wild type flu viruses, such as 2009 pandemic H1N1 flu. Here we developed a simple and sensitive screening assay for wild type influenza A virus by quantitatively analyzing viral protein levels using a Dot Blot Assay in combination with the LI-COR Imaging System (DBALIS). We first validated DBALIS in overexpression and RNAi assays, which are suitable methods for screening host factors regulating viral infection. More importantly, we also validated and initiated drug screening using DBALIS. A pilot compound screening identified a small molecule that inhibited influenza A virus infection. Taken together, our method represents a reliable and convenient high throughput assay for screening novel host factors and antiviral compounds
Relationship between antibiotic resistance, biofilm formation, and biofilm-specific resistance in Acinetobacter baumannii
No full textIn this study, we aimed to examine the relationships between antibiotic resistance, biofilm formation, and biofilm-specific resistance in clinical isolates of Acinetobacter baumannii. The tested 272 isolates were collected from several hospitals in China during 2010–2013. Biofilm-forming capacities were evaluated using the crystal violet staining method. Antibiotic resistance/susceptibility profiles to 21 antibiotics were assessed using VITEK 2 system, broth microdilution method or the Kirby-Bauer disc diffusion method. The minimum biofilm eradication concentration (MBEC) to cefotaxime, imipenem, and ciprofloxacin were evaluated using micro dilution assays. Genetic relatedness of the isolates was also analysed by pulsed-field gel electrophoresis (PFGE) and plasmid profile. Among all the 272 isolates, 31 were multidrug-resistant (MDR), and 166 were extensively drug-resistant (XDR). PFGE typing revealed 167 pattern types and 103 clusters with a similarity of 80%. MDR and XDR isolates built up the main prevalent genotypes. Most of the non-MDR isolates were distributed in a scattered pattern. Additionally, 249 isolates exhibited biofilm formation, among which 63 were stronger biofilm formers than type strain ATCC19606. Population that exhibited more robust biofilm formation likely contained larger proportion of non-MDR isolates. Isolates with higher level of resistance tended to form weaker biofilms. The MBECs for cefotaxime, imipenem, and ciprofloxacin showed a positive correlation with corresponding MICs, while the enhancement in resistance occurred independent of the quantity of biofilm biomass produced. We suppose from this study that biofilm acts as a mechanism for bacteria to get a better survival, especially in isolates with resistance level not high enough. Moreover, even though biofilms formed by isolates with high level of resistance are always weak, they could still provide similar level of protection for the isolates. Further explorations genetically would improve our understanding of these processes and provide novel insights in the therapeutics and prevention against A. baumannii biofilm-related infections
DNA demethylation upregulated Nrf2 expression in Alzheimer's disease cellular model
No full textNuclear factor erythroid 2-related factor 2 (Nrf2) is an important transcription factor in the defense against oxidative stress. Cumulative evidence has shown that oxidative stress plays a key role in the pathogenesis of Alzheimer's disease (AD). Previous animal and clinical studies had observed decreased expression of Nrf2 in AD. However, the underlying regulation mechanisms of Nrf2 in AD remain unclear. Here, we used the DNA methyltransferases (Dnmts) inhibitor 5-aza-2′-deoxycytidine (5-Aza) to test whether Nrf2 expression was regulated by methylation in N2a cells characterizing by expressing human Swedish mutant amyloid precursor protein (N2a/APPswe). We found 5-Aza treatment increased Nrf2 at both mRNA and protein levels via down-regulating the expression of Dnmts and DNA demethylation. In addition, 5-Aza mediated upregulation of Nrf2 expression was concomitant with increased nuclear translocation of Nrf2 and higher expression of Nrf2 downstream target gene NAD(P)H:quinone oxidoreductas (NQO1). Our study showed that DNA demethylation promoted the Nrf2 cell signaling pathway, which may enhance the antioxidant system against AD development
