The properties of the complex between ribosomal protein L2 and tRNA

Escherichia coli ribosomal protein L2 interacts with fMet-tRNA^Met and NacPhe-tRNA^Phe in solution, protecting their 3'-ends from enzymatic degradation. At the same time L2 enhances the rate of spontaneous hydrolysis of the ester bonds between terminal riboses and amino acyl moieties of these two peptidyl-tRNA analogues. L2 has, however, only a slight effect on the rate of spontaneous deacylation of aminoacyltRNAs. We suggest that the role of L2 is in the fixation of the aminoacyl stem of tRNA to the ribosome at its P-site, and speculate that this protein is directly involved in the peptidyl transferase (PT) reaction. Peptidyl transferase Protein L2 tRNA-protein complex     

Thymopentin antagonizes stress-induced changes of GABA/benzodiazepine receptor complex

Intraperitoneal administration of thymopentin, a thymopentin II-derived pentapeptide, had no stable and evident effect in the two anxiety models (elevated plus-maze and licking-conflict test) studied. However, in the elevated plus-maze test thymopentin antagonized the behavioral effects of DMCM, a beta-carboline derivative with anxiogenic properties. Further, it was demonstrated that the licking-conflict test procedure itself produced a significant elevation of plasma corticosterone levels, increased the number of [3H]flunitrazepam and decreased the number of [3H]muscimol binding sites in rat hippocampus. The forced-swimming stress similarly to the licking-conflict test also caused an increase in hippocampal [3H]flunitrazepam binding sites. Although ineffective behaviorally in the tests for anxiety, thymopentin pretreatment effectively reversed the changes in corticosterone levels caused by the licking-conflict test. Moreover, it normalized the changed number of benzodiazepine and GABA receptors after stressful stimuli. It is well known that not all anxiolytic drugs (i.e. buspirone) are equally active in behavioral tests for anxiety. According to our data we propose that thymopentin has stress-protective activity. As in vivo and in vitro thymopentin did not change [3H]-flunitrazepam and [3H]muscimol binding, the direct effect of this peptide on the GABA-benzodiazepine-Cl- ionophore receptor complex is unlikely. The action of this peptide on GABA release and/or metabolism can be suggested.     

Lsamp–/– mice display lower sensitivity to amphetamine and have elevated 5-HT turnover

In mice, the limbic system-associated membrane protein (Lsamp) gene has been implicated in locomotion, anxiety, fear reaction, learning, social behaviour and adaptation. Human data links the LSAMP gene to several psychiatric disorders and completed suicide. Here, we investigated changes in major monoamine systems in mice lacking the Lsamp gene. First, the locomotor and rewarding effects of amphetamine were studied in Lsamp^–/– mice and Lsamp^+/+ mice. Second, monoamine levels in major brain regions in response to saline and amphetamine injections were measured and, third, the expression levels of dopamine system-related genes in the brain were studied in these mice. Lsamp^–/– mice displayed lower sensitivity to amphetamine in the motility box. Likewise, in the place preference test, the rewarding effect of amphetamine was absent in Lsamp^–/– mice. In all brain regions studied, Lsamp^–/– mice displayed lower serotonin (5-HT) baseline levels, but a greater 5-HT turnover rate, and amphetamine increased the level of 5-HT and lowered 5-HT turnover to a greater extent in Lsamp^–/– mice. Finally, Lsamp^–/– mice had lower level of dopamine transporter (DAT) mRNA in the mesencephalon. In conclusion, Lsamp-deficiency leads to increased endogenous 5-HT-ergic tone and enhanced 5-HT release in response to amphetamine. Elevated 5-HT function and reduced activity of DAT are the probable reasons for the blunted effects of amphetamine in these mice. Lsamp^–/– mice are a promising model to study the neurobiological mechanisms of deviant social behaviour and adaptation impairment observed in many psychiatric disorders.     

New strigolactone mimics: Structure–activity relationship and mode of action as germinating stimulants for parasitic weeds

Strigolactones (SLs) are new plant hormones with varies important bio-functions. This Letter deals with germination of seeds of parasitic weeds. Natural SLs have a too complex structure for synthesis. Therefore, there is an active search for SL analogues and mimics with a simpler structure with retention of activity. SL analogues all contain the D-ring connected with an enone moiety through an enol ether unit. A new mechanism for the hydrolysis SL analogues involving bidentate bound water and an α,β-hydrolase with a Ser-His-Asp catalytic triad has been proposed. Newly discovered SL mimics only have the D-ring with an appropriate leaving group at C-5. A mode of action for SL mimics was proposed for which now supporting evidence is provided. As predicted an extra methyl group at C-4 of the D-ring blocks the germination of seeds of parasitic weeds.     

Substrate specificity of the pseudouridine synthase RluD in Escherichia coli

Pseudouridine synthase RluD converts uridines at positions 1911, 1915, and 1917 of 23S rRNA to pseudouridines. These nucleotides are located in the functionally important helix-loop 69 of 23S rRNA. RluD is the only pseudouridine synthase that is required for normal growth in Escherichia coli. We have analyzed substrate specificity of RluD in vivo. Mutational analyses have revealed: (a) RluD isomerizes uridine in vivo only at positions 1911, 1915, and 1917, regardless of the presence of uridine at other positions in the loop of helix 69 of 23S rRNA variants; (b) substitution of one U by C has no effect on the conversion of others (i.e. formation of pseudouridines at positions 1911, 1915, and 1917 are independent of each other); (c) A1916 is the only position in the loop of helix 69, where mutations affect the RluD specific pseudouridine formation. Pseudouridines were determined in the ribosomal particles from a ribosomal large subunit defective strain (RNA helicase DeaD(-)). An absence of pseudouridines in the assembly precursor particles suggests that RluD directed isomerization of uridines occurs as a late step during the assembly of the large ribosomal subunit.     

Increased behavioural activity of rats in forced swimming test after partial denervation of serotonergic system by parachloroamphetamine treatment

The present study aimed at characterizing the effect of partial 5-HT denervation by parachloroamphetamine (PCA), a 5-HT selective neurotoxin, on forced swimming behaviour and monoamine levels in several rat brain regions. PCA was administered intraperitoneally in two independent experiments in doses of 2, 4 and 6 mg/kg and in doses 1, 2, 4 mg/kg, respectively. PCA (2 mg/kg) reduced immobility in the forced swimming test in the Experiment 1 and according to Experiment 2 this is explained by increased swimming time. Dose-dependent reductions in 5-HT and 5-HIAA levels were found in all brain regions studied, and the maximal effects were of a similar magnitude. In septum, the effect of PCA took more time to develop. The effects of the lowest dose of PCA suggest that the neurotoxin affects not only the dorsal raphe projection areas but also the fine axons which arise from the median raphe. alpha2-Adrenoceptors and beta-adrenoceptors in cerebral cortex were not affected by the PCA treatment. Binding affinity of the 5-HT(1A) receptors was higher after all doses of PCA. On the second exposure to the forced swimming the time spent in swimming was found to be negatively and the time spent in immobile posture positively correlated with serotonin turnover in frontal cortex. The time spent in struggling on the second exposure to test was found to be negatively correlated with KD of beta-adrenoceptor binding in cerebral cortex. These data suggest that partial 5-HT denervation with low doses of PCA, which elicits a specific pattern of neurodegeneration, results in an increased behavioural activity, and that the traditional interpretation of the measures in forced swimming test, despite of the test's predictive power in revealing antidepressants acting on monoaminergic systems, is not adequate for studies on the neurochemical basis of depression.     

Terpenoid metabolism in wild-type and transgenic Arabidopsis plants

Volatile components, such as terpenoids, are emitted from aerial parts of plants and play a major role in the interaction between plants and their environment. Analysis of the composition and emission pattern of volatiles in the model plant Arabidopsis showed that a range of volatile components are released, primarily from flowers. Most of the volatiles detected were monoterpenes and sesquiterpenes, which in contrast to other volatiles showed a diurnal emission pattern. The active terpenoid metabolism in wild-type Arabidopsis provoked us to conduct an additional set of experiments in which transgenic Arabidopsis overexpressing two different terpene synthases were generated. Leaves of transgenic plants constitutively expressing a dual linalool/nerolidol synthase in the plastids (FaNES1) produced linalool and its glycosylated and hydroxylated derivatives. The sum of glycosylated components was in some of the transgenic lines up to 40- to 60-fold higher than the sum of the corresponding free alcohols. Surprisingly, we also detected the production and emission of nerolidol, albeit at a low level, suggesting that a small pool of its precursor farnesyl diphosphate is present in the plastids. Transgenic lines with strong transgene expression showed growth retardation, possibly as a result of the depletion of isoprenoid precursors in the plastids. In dual-choice assays with Myzus persicae, the FaNES1-expressing lines significantly repelled the aphids. Overexpression of a typical cytosolic sesquiterpene synthase resulted in the production of only trace amounts of the expected sesquiterpene, suggesting tight control of the cytosolic pool of farnesyl diphosphate, the precursor for sesquiterpenoid biosynthesis. This study further demonstrates the value of Arabidopsis for studies of the biosynthesis and ecological role of terpenoids and provides new insights into their metabolism in wild-type and transgenic plants.     

Secondary metabolite signalling in host-parasitic plant interactions

The parasitic weeds Orobanche and Striga spp. are a serious threat to agriculture in large parts of the world. The lifecycle of the parasitic weeds is closely regulated by the presence of their hosts, and secondary metabolites that are produced by host plants play an important role in this interaction. Model plants, such as Arabidopsis and maize mutant collections, have been increasingly used to study these chemical signals, especially those host-produced stimulants that induce the germination of parasite seeds.