A crevice adjoining the ribosome tunnel: hints for cotranslational folding

RNA protection experiments and the crystal structure of a complex of the large ribosomal subunit from the eubacterium Deinococcus radiodurans with rapamycin, a polyketide compound resembling macrolides and ketolides, showed that rapamycin binds to a crevice located at the boundaries of the nascent protein exit tunnel, near its entrance. At this location rapamycin cannot occlude the ribosome exit tunnel, consistent with its failure to act as a ribosomal antibiotic drug. In accord with recent biochemical data, this crevice may play a role in facilitating local cotranslational folding of nascent chains, in particular for transmembrane proteins.     

Azospirillum brasilense does not affect population structure of specific rhizobacterial communities of inoculated maize (Zea mays)

Positive response of plant species to plant growth-promoting rhizobacteria have led to an increased interest in their use as bacterial inoculants. However, the introduction of exogenous bacteria into natural ecosystems may perturb bacterial populations within the microbial community and lead to the disruption of indigenous populations performing key functional roles. In this study the effect of Azospirillum brasilense inoculation on maize (Zea mays) rhizosphere Actinobacteria, Bacteroidetes, alpha-Proteobacteria, Pseudomonas and Bdellovibrio spp. was assessed using a polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) approach in conjunction with group-specific primers. The DGGE fingerprints analysis revealed that the introduction of A. brasilense did not alter or disrupt the microbial system at the group-specific level. However, some communities such as the alpha-Proteobacteria and Bdellovibrio were influenced by plant age while the other bacterial groups remained unaffected. Based on these as well as previous data, it can be inferred that inoculation with A. brasilense does not perturb the natural bacterial populations investigated.     

Crystal structures of complexes of the small ribosomal subunit with tetracycline, edeine and IF3

The small ribosomal subunit is responsible for the decoding of genetic information and plays a key role in the initiation of protein synthesis. We analyzed by X-ray crystallography the structures of three different complexes of the small ribosomal subunit of Thermus thermophilus with the A-site inhibitor tetracycline, the universal initiation inhibitor edeine and the C-terminal domain of the translation initiation factor IF3. The crystal structure analysis of the complex with tetracycline revealed the functionally important site responsible for the blockage of the A-site. Five additional tetracycline sites resolve most of the controversial biochemical data on the location of tetracycline. The interaction of edeine with the small subunit indicates its role in inhibiting initiation and shows its involvement with P-site tRNA. The location of the C-terminal domain of IF3, at the solvent side of the platform, sheds light on the formation of the initiation complex, and implies that the anti-association activity of IF3 is due to its influence on the conformational dynamics of the small ribosomal subunit.     

Resource-island soils and the survival of the giant cactus,cardon, of Baja California Sur

Early survival and growth of some plants in arid environments depends on facilitation by a nurse plant. Amelioration of soil temperature extremes through shading and accumulation of mineral nutrients near nurse-plants are mechanisms of facilitation. We investigated the effects of shading (soil temperature) and soil type on survival and growth of the giant columnar cactus, cardon (Pachycereus pringlei). Cardon was grown either in a sandy clay-loam soil obtained from resource islands formed under mature mesquite (Prosopis articulata) or in the loamy-sand soil from plant-free bare areas that surround the islands. Seedlings were potted in these soils and the pots were buried to ground level in the open. We also determined plant responses to fertilization with N, P, K or NPK in the bare-area soils. Enhancement of survival and growth in the resource-island soils compared to that in the bare-area soils was highly significant. Plants survived and grew better in resource-island soils than in bare-area soil, an effect that was enhanced by shading (one-half of full sun). Greater root/shoot ratios of plants grown in bare-area soil indicated increased resource allocation to roots under limiting conditions. Significant interactions (analysis of variance) indicated that the soil and sun factors of the experiment were not independent of one another. Plant growth in bare-area soil improved considerably (>200%) in response to N fertilization (screenhouse conditions), and approximated that of plants in resource-island soil without N amendment. The growth response to P was small (<50%), while K did not affect growth significantly. Responses to NPK were similar to those to N alone. The results suggested that shading and nutritional effects interact in determining early survival and growth of cardon in different soils. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Synergistic Effect of Visible Light and Gentamycin on Pseudomona aeruginosa Microorganisms

Recently there were several publications on the bactericidal effect of visible light, most of them claiming that blue part of the spectrum (400 nm-500 nm) is responsible for killing various pathogens^1-5. The phototoxic effect of blue light was suggested to be a result of light-induced reactive oxygen species (ROS) formation by endogenous bacterial photosensitizers which mostly absorb light in the blue region^4,6,7. There are also reports of biocidal effect of red and near infra red⁸ as well as green light⁹.In the present study, we developed a method that allowed us to characterize the effect of high power green (wavelength of 532 nm) continuous (CW) and pulsed Q-switched (Q-S) light on Pseudomonas aeruginosa. Using this method we also studied the effect of green light combined with antibiotic treatment (gentamycin) on the bacteria viability. P. aeruginosa is a common noscomial opportunistic pathogen causing various diseases. The strain is fairly resistant to various antibiotics and contains many predicted AcrB/Mex-type RND multidrug efflux systems¹⁰.The method utilized free-living stationary phase Gram-negative bacteria (P. aeruginosa strain PAO1), grown in Luria Broth (LB) medium exposed to Q-switched and/or CW lasers with and without the addition of the antibiotic gentamycin. Cell viability was determined at different time points. The obtained results showed that laser treatment alone did not reduce cell viability compared to untreated control and that gentamycin treatment alone only resulted in a 0.5 log reduction in the viable count for P. aeruginosa. The combined laser and gentamycin treatment, however, resulted in a synergistic effect and the viability of P. aeruginosa was reduced by 8 log''s.The proposed method can further be implemented via the development of catheter like device capable of injecting an antibiotic solution into the infected organ while simultaneously illuminating the area with light.     

Distribution of Glutamate Transporter Subtypes During Human Brain Development

Abstract: In the mature brain, removal of glutamate from the synaptic cleft plays an important role in the maintenance of subtoxic levels of glutamate. This requirement is handled by a family of glutamate transporters, EAAT1, EAAT2, EAAT3, and EAAT4. Due to the involvement of glutamate also in neuronal development, it is believed that glutamate transport plays a role in developmental processes as well. Therefore, we have used immunohistochemical and immunoblot analysis to determine the distribution of the four glutamate transporters during human brain development using human pre- and postnatal brain tissue. Regional analysis showed that each transporter subtype has a unique distribution during development. EAAT2 was the most prominent glutamate transporter subtype and was highly enriched in cortex, basal ganglia, cerebellum, and thalamus in all ages examined. EAAT1 immunoreactivity was lower than that of EAAT2, with predominant localization in cortex, basal ganglia, hippocampus, and periventricular region. EAAT3 was located mainly in cortex, basal ganglia, and hippocampus, and EAAT4 was found only in cortex, hippocampus, and cerebellar cortex. The distinct regional distribution of various EAAT subtypes and also the transient expression of specific EAAT subtypes during development suggest multiple functional roles for glutamate transporters in the developing brain.     

Listeria monocytogenes Multidrug Resistance Transporters and Cyclic Di-AMP,Which Contribute to Type I Interferon Induction,Play a Role in Cell Wall Stress

The intracellular bacterial pathogen Listeria monocytogenes activates a robust type I interferon response upon infection. This response is partially dependent on the multidrug resistance (MDR) transporter MdrM and relies on cyclic-di-AMP (c-di-AMP) secretion, yet the functions of MdrM and cyclic-di-AMP that lead to this response are unknown. Here we report that it is not MdrM alone but a cohort of MDR transporters that together contribute to type I interferon induction during infection. In a search for a physiological function of these transporters, we revealed that they play a role in cell wall stress responses. A mutant with deletion of four transporter genes (ΔmdrMTAC) was found to be sensitive to sublethal concentrations of vancomycin due to an inability to produce and shed peptidoglycan under this stress. Remarkably, c-di-AMP is involved in this phenotype, as overexpression of the c-di-AMP phosphodiesterase (PdeA) resulted in increased susceptibility of the ΔmdrMTAC mutant to vancomycin, whereas overexpression of the c-di-AMP diadenylate cyclase (DacA) reduced susceptibility to this drug. These observations suggest a physiological association between c-di-AMP and the MDR transporters and support the model that MDR transporters mediate c-di-AMP secretion to regulate peptidoglycan synthesis in response to cell wall stress.     

Quantitative autoradiography of neurochemicals

Several new methods have been developed that apply quantitative autoradiography to neurochemistry. These methods are derived from the 2-deoxyglucose (2DG) technique of Sokoloff (1), which uses quantitative autoradiography to measure the rate of glucose utilization in brain structures. The new methods allow the measurement of the rate of cerbral protein synthesis and the levels of particular neurotransmitter receptors by quantitative autoradiography. As with the 2DG method, the new techniques can measure molecular levels in micron-sized brain structures; and can be used in conjuction with computerized systems of image processing. It is possible that many neurochemical measurements could be made by computerized analysis of quantitative autoradiograms.