Which agonist properties are important for the activation of 5-HT3A receptors?

Purpose: Why do anesthetics not activate excitatory ligand-gated ion channels such as 5-HT₃ receptors in contrast to inhibitory ligand-gated ion channels? This study examines the actions of structural closely-related 5-HT derivatives and 5-HT constituent parts on 5-HT_3A receptors with the aim of finding simpler if not minimal agonists and thus determining requirements for successful agonist action. Experimental approach: Responses to 5-HT derivatives of human 5-HT_3A receptors stably expressed in HEK 293 cells have been examined with the patch-clamp technique in the outside-out configuration combined with a fast solution exchange system. Results: Phenol, pyrrole and alkyl amines, constituents of 5-HT, even at high concentrations, cannot activate 5-HT_3A receptors but they can inhibit them. To date, tyramines are the smallest known agonists. However, an aromatic ring is not required for activation as acetylcholine is also an agonist of similar strength. Conclusion: Simultaneous interactions of adequate strength at two separate subsites within the 5-HT binding domain appear to be essential for successful agonist function. Anesthetics either fail to achieve this or the activation they produce is so weak that it is masked by a comparatively very strong inhibition.     

Databases as instruments for analysis of large-scale data sets of interactions between molecular biological objects

We have surveyed the most well-known and accessible information resources, consolidating data on interactions of molecular biological objects. Three main criteria are discussed: quality (coverage and reliability) of the information present, ability to analyze experimental data, and ease of results visualization. Several algorithms of data analysis, based on various types of resources, and statistics for its evaluation are named.     

Hormetic doses of UV-C light decrease the susceptibility of tomato plants to Botrytis cinerea infection

Preharvest hormetic doses of UV-C radiation can decrease the susceptibility of tomato leaves to Botrytis cinerea L. infection. UV-C light treatments have been shown to be very effective for reducing disease development in several species, including tomato (Solanum lycopersicum L.). Treating cultivated tomato plants with UV-C light is of interest not only because of the disinfecting effects of UV-C light but also because of its ability to stimulate plant defences (SDP) against diseases, provided that the applied doses are high enough to be effective while low enough to prevent deleterious effects. In the present study, the effects of UV-C light on plants were evaluated by biochemical analyses, including analyses of the activities of antioxidant enzymes and phenylalanine lyase (PAL); the concentration of malondialdehyde (MDA), an indicator of membrane integrity; and chlorophyll fluorescence parameters, such as the maximum quantum efficiency of photosystem II (F_V/F_M) and the Strasser performance index (PI). In this work, treatments with single doses of 0.85 kJ/m² of UV-C light were found to significantly increase plant defences against B. cinerea, reducing the affected leaf area by 51% compared to the affected area of control plants. This decrease in susceptibility was associated with increased PAL activity and the amount of bound phenolics compared to levels in control plants (not treated with UV-C).     

Effect of leaf-to-fruit ratio on leaf nitrogen content and net photosynthesis in girdled branches of Mangifera indica L.

Variations in leaf nitrogen concentration (N_m), mass-to-area ratio (M_a), amount of leaf nitrogen per unit leaf area (N_a), and non-structural carbohydrates were measured in well-lit girdled branches of 11-year-old mango trees that were experiencing similar conditions of irradiance and gap fraction. The influence of source–sink relationships was studied by testing three levels of leaf-to-fruit ratio: 40, 70 and 150, during the period of linear fruit growth. N_a was negatively correlated to the leaf-to-fruit ratio. Differences in N_a were reflected in differences in net photosynthetic assimilation, A_net, although they could not fully account for them. All differences in N_a resulted exclusively from differences in N_m, not M_a. Starch and total non-structural carbohydrates accumulated in the leaves as the result of higher leaf-to-fruit ratio, which suggests that the leaf carbohydrate status may play a role in photosynthetic acclimation to fruit load in mango. These observations complement previous findings where photosynthetic acclimation to light was found to be driven by changes in M_a, while N_m remained almost constant over a large range of gap fractions. Observations about the effect of fruit load were also in contrast with previous observations, since no evidence was found that leaf carbohydrate status played any role in photosynthetic acclimation to light. This study demonstrates that acclimation to changing source–sink relationships does not follow the same pattern as acclimation to progressive shading; but these observations do suggest that there may be different mechanisms by which leaves acclimatise to changing conditions.     

Biological evidence for a precursor protein of serum albumin.

Radioactive leucine was injected into the portal vein of rats followed after 15 seconds by a 180 fold excess of nonradioactive leucine. An albumin-like protein in the liver became highly labelled within 15 minutes after injection. After 150 minutes, the radioactivity in the albumin-like protein had decreased to one tenth. In the serum, radioactively labelled albumin started to appear after 15 minutes and increased there-after up to 150 minutes after injection. Radioactivity in albumin within the liver remained constant at a low level. These results suggest that the albumin-like protein is a biological precursor protein of serum albumin, i.e. a proalbumin.     

An assay for functional dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) inhibitors of human dendritic cell adhesion

We report a new dendritic cell adhesion assay, using either immature or mature dendritic cells, for identifying functional dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) inhibitors. Because immature dendritic cells are responsible for pathogen binding and invasion, this in vitro assay provides an important link between in vitro results and pathogen-based in vivo assays. Furthermore, this assay does not require laborious expression, refolding, and purification of DC-SIGN carbohydrate recognition domain or extracellular domain as receptor-based assays. The assay power evaluated with Z and Z′ parameters enables screening of compound libraries and determination of IC₅₀ values in the first stage of DC-SIGN inhibitor development.     

Structure-based virtual screening of hypothetical inhibitors of the enzyme longiborneol synthase—a potential target to reduce <Emphasis Type="Italic">Fusarium</Emphasis> head blight disease

Fusarium head blight (FHB) is one of the most destructive diseases of wheat and other cereals worldwide. During infection, the Fusarium fungi produce mycotoxins that represent a high risk to human and animal health. Developing small-molecule inhibitors to specifically reduce mycotoxin levels would be highly beneficial since current treatments unspecifically target the Fusarium pathogen. Culmorin possesses a well-known important synergistically virulence role among mycotoxins, and longiborneol synthase appears to be a key enzyme for its synthesis, thus making longiborneol synthase a particularly interesting target. This study aims to discover potent and less toxic agrochemicals against FHB. These compounds would hamper culmorin synthesis by inhibiting longiborneol synthase. In order to select starting molecules for further investigation, we have conducted a structure-based virtual screening investigation. A longiborneol synthase structural model is first built using homology modeling, followed by molecular dynamics simulations that provided the required input for a protein–ligand ensemble docking procedure. From this strategy, the three most interesting compounds (hits) were selected among the 25 top-ranked docked compounds from a library of 15,000 drug-like compounds. These putative inhibitors of longiborneol synthase provide a sound starting point for further studies involving molecular modeling coupled to biochemical experiments. This process could eventually lead to the development of novel approaches to reduce mycotoxin contamination in harvested grain.     

Can small‐scale experiments predict ecosystem responses? An example from peatlands

Oligotrophic, Sphagnum -dominated peatlands have been regarded as long-term stable ecosystems that function as carbon sinks. As a result of environmental perturbations, particularly anthropogenic N deposition, this view is now increasingly questioned. We examined whether small-scale field experiments can predict the direction and magnitude of ecosystem responses to increased N supply. We, therefore, compared data from a 10-year field experiment (involving deposition of 2, 15 and 30 kg N ha⁻¹ year⁻¹) with data from a gradient associated with increased N deposition (2, 8 and 12 kg N ha⁻¹ year⁻¹). We chose to compare: (1) the physiological response of Sphagnum balticum , measured in the form of N accumulation as free amino acids (N_AA); and (2) changes in the total Sphagnum cover, the cover of S. balticum , and vascular plant cover. In all cases we found a highly significant correlation between the two data sets. We attribute the high correspondence between the two data sets to the key function of the dominant group of organisms, the Sphagna, that monopolize N availability and control the water balance, creating an environment hostile to vascular plants. Thus the key role of Sphagna as ecosystem engineers seems to supersede the role of other, scale-dependent processes. We also conclude that N_AA is a sensitive indicator that can be used to signal the slow and gradual shift from Sphagnum to vascular plant dominance.     

Stepwise immunologic selection of antigenic variants during tumor growth

Using tumor-specific effector cells as probes, we have studied the immunologic changes that occur in tumor cells during continuous growth in a host. As a model, we used a highly immunogenic ultraviolet light (UV)-induced tumor that is rejected regularly by normal mice but grows progressively when transplanted into UV-irradiated mice. The immunogenic tumor growing continuously in these partially immunocompromised mice gave rise to genetically stable progressor variants that were poorly immunogenic. A sequence of changes in susceptibility to activated macrophages and tumor-specific cytolytic T cells was observed when serial reisolates from the continuously growing tumors were analyzed. First, the tumor cells developed resistance to the cytocidal effects of activated macrophages. This was followed by the loss of one and then a second tumor-specific antigen defined by syngeneic cytolytic T cells. The phenotypes of the developing antigen loss variants and their sequence of appearance were the same in several independent experiments, and the process was apparently determined by a hierarchy of the host's immune response to multiple independent tumor-specific antigens expressed by a single malignant cell. Our ability to generate the predicted variants in vitro before they actually appear in vivo suggests a possible approach to preventing the outgrowth of such immunoselected variants from a tumor.