Tertiary structure of bacterial selenocysteine tRNA

Selenocysteine (Sec) is translationally incorporated into proteins in response to the UGA codon. The tRNA specific to Sec (tRNA^Sec) is first ligated with serine by seryl-tRNA synthetase (SerRS). In the present study, we determined the 3.1 Å crystal structure of the tRNA^Sec from the bacterium Aquifex aeolicus, in complex with the heterologous SerRS from the archaeon Methanopyrus kandleri. The bacterial tRNA^Sec assumes the L-shaped structure, from which the long extra arm protrudes. Although the D-arm conformation and the extra-arm orientation are similar to those of eukaryal/archaeal tRNA^Secs, A. aeolicus tRNA^Sec has unique base triples, G14:C21:U8 and C15:G20a:G48, which occupy the positions corresponding to the U8:A14 and R15:Y48 tertiary base pairs of canonical tRNAs. Methanopyrus kandleri SerRS exhibited serine ligation activity toward A. aeolicus tRNA^Sec in vitro. The SerRS N-terminal domain interacts with the extra-arm stem and the outer corner of tRNA^Sec. Similar interactions exist in the reported tRNA^Ser and SerRS complex structure from the bacterium Thermus thermophilus. Although the catalytic C-terminal domain of M. kandleri SerRS lacks interactions with A. aeolicus tRNA^Sec in the present complex structure, the conformational flexibility of SerRS is likely to allow the CCA terminal region of tRNA^Sec to enter the SerRS catalytic site.     

Mother–calf interactions and social behavior development in Commerson’s dolphins (Cephalorhynchus commersonii)

Mother–calf interactions and the behaviors of mothers during separation from their calves were examined in four Commerson’s dolphin (Cephalorhynchus commersonii) mother–calf pairs. Four infants were observed: 56.8 h over 30 days from birth to 263 days of age, 36.9 h over 20 days from birth to 149 days of age, 10.4 h over 3 days from birth to 2 days of age, and 15.0 h over 3 days from birth to 2 days of age. All four pairs shared common characteristics in the rate and frequencies of mother–calf interactions and the behaviors of mothers during the first week of life. After the first week, individual differences in changes in the frequency of each behavior were observed. The three behaviors considered representative of maternal care (parallel swimming, synchronous breathing, and body-to-body contact) were frequently performed in the first week; thereafter, the frequencies declined. Separate behaviors of mothers were infrequent during the first week and increased with an increase in infants’ age. Bumping by infants increased with time, suggesting an increase in soliciting by calves and conflict between mothers and calves. The frequency of flipper-to-body rubbing also changed but in a complex manner, probably because the calves needed to learn how to perform this behavior from their mothers and because initiator and recipient of this behavior can be changed quickly.     

Novel Twin Streptolysin S-Like Peptides Encoded in the sag Operon Homologue of Beta-Hemolytic Streptococcus anginosus

Streptococcus anginosus is a member of the anginosus group streptococci, which form part of the normal human oral flora. In contrast to the pyogenic group streptococci, our knowledge of the virulence factors of the anginosus group streptococci, including S. anginosus, is not sufficient to allow a clear understanding of the basis of their pathogenicity. Generally, hemolysins are thought to be important virulence factors in streptococcal infections. In the present study, a sag operon homologue was shown to be responsible for beta-hemolysis in S. anginosus strains by random gene knockout. Interestingly, contrary to pyogenic group streptococci, beta-hemolytic S. anginosus was shown to have two tandem sagA homologues, encoding streptolysin S (SLS)-like peptides, in the sag operon homologue. Gene deletion and complementation experiments revealed that both genes were functional, and these SLS-like peptides were essential for beta-hemolysis in beta-hemolytic S. anginosus. Furthermore, the amino acid sequence of these SLS-like peptides differed from that of the typical SLS of S. pyogenes, especially in their propeptide domain, and an amino acid residue indicated to be important for the cytolytic activity of SLS in S. pyogenes was deleted in both S. anginosus homologues. These data suggest that SLS-like peptides encoded by two sagA homologues in beta-hemolytic S. anginosus may be potential virulence factors with a different structure essential for hemolytic activity and/or the maturation process compared to the typical SLS present in pyogenic group streptococci.     

Hit-to-lead optimization of 2-(1H-pyrazol-1-yl)-thiazole derivatives as a novel class of EP1 receptor antagonists

We describe a medicinal chemistry approach to generate a series of 2-(1H-pyrazol-1-yl)thiazole compounds that act as selective EP₁ receptor antagonists. The obtained results suggest that compound 12 provides the best EP₁ receptor antagonist activity and demonstrates good oral pharmacokinetics.     

Excitotoxicity-induced immediate surge in hippocampal prostanoid production has latent effects that promote chronic progressive neuronal death

Excitotoxicity is involved in neurodegenerative conditions. We investigated the pathological significance of a surge in prostaglandin production immediately after kainic acid (KA) administration [initial phase], followed by a sustained moderate elevation in prostaglandin level [late phase] in the hippocampus of juvenile rats. Numerous pyknotic hippocampal neurons were observed 72 h after KA treatment; this number remained elevated on days 10 and 30. Gross hippocampal atrophy was observed on days 10 and 30. Pre-treatment with indomethacin ameliorated neuronal death on days 10 and 30, and prevented hippocampal atrophy on day 30. Microglial response was moderated by the indomethacin pre-treatment. Blockade of only late-phase prostaglandin production by post-treatment with indomethacin ameliorated neuronal death on day 30. These findings suggest a role for initial-phase prostaglandin production in chronic progressive neuronal death, which is exacerbated by late-phase prostaglandin production. Blockade of prostaglandin production has therapeutic implications in preventing long-term neurological sequelae following excitotoxic brain damage.     

Chemical Synthesis and Characterization of α-N-Octanoyl and Other α-N-Acyl Colistin Nonapeptide Derivatives

Eight α-N-acyl colistin nonapeptide derivatives including three aliphatic, four aromatic and one alicyclic derivatives were synthesized by the reaction of colistin nonapeptide with corresponding acid chlorides. This acylation reaction was carried out under the condition kept restrictedly at pH 5,0 in order to introduce an acyl group only to α-amino group but not to γ-amino group existing in a colistin nonapeptide molecule. Synthetic method and several physico-chemical natures of these acyl colistin nonapeptide derivatives are given in this paper.

All of the acylated derivatives thus synthesized exhibited characteristic antimicrobial activities. Antimicrobial spectra were substantially based upon a gram-negative type and not so much altered by chemical structures of acyl groups which were considerably differentiated from each other such as cyclic or chain form. Thus, more possible response of carbon size than its structure to the antimicrobial effectiveness was inferred. In spite of almost no toxicity and feeble antimicrobial activity of colistin nonapeptide itself, these acylated colistin nonapeptide derivatives showed a toxicity against mice at a dose of 16.9~70 mg/kg in LD₅₀, which, however, was inferior to the toxicity of colistin sulfate, possibly correspondent to their much weaker antimicrobial activities, as a whole. Hence, it seems likely that acyl part of these acylated colistin nonapeptide derivatives including that of colistin is seriously responsible for the biological activities.     

Ruminal Fermentation and Sugar Concentrations

The maximal amounts of growth of Selenomonas ruminantium were examined in the media containing various amounts of glucose. The yields of cells per unit weight of glucose are linear functions to glucose concentrations in the ranges between zero to 0.005% and 0.005 to 0.7%, Cell yields per glucose are greater in the former range, indicating greater a-mounts of energy are available per glucose at lower concentrations. Growth responses in lactate media containing various amounts of glucose showed that the preincubation with larger amounts of glucose is inhibitory for the following growth and metabolism of lactate. The organism produces predominantly lactate in the glucose medium. However, volatile fatty acid productions increase when the initial concentrations of glucose become low. Isotopic studies showed that the lactate utilization yielding volatile fatty acids is inhibited by the preceding metabolism of high concentrations of glucose. These results were discussed with regard to normal and abnormal fermentations in the rumen.     

Studies on Growth Inhibition of Hiochi-bacteria,Specific Saprophytes of Sake

A new growth inhibitant against hiochi-bacteria, C₁₁H₁₈N₂O, m.p. 173~4°C, named muta-aspergillic acid, has been isolated from the crystals of crude hydroxyaspergillic acid, obtained from culture filtrate of Asp. oryzae. Successful separation of these two compounds from each other was accomplished by counter current distribution method. The physical and chemical properties of muta-aspergillic acid as well as its physiological properties are described.