Dimerization of long hibernation promoting factor from Staphylococcus aureus: Structural analysis and biochemical characterization.

Staphylococcus aureus hibernation promoting factor (SaHPF) is responsible for the formation of 100S ribosome dimers, which in turn help this pathogen to reduce energy spent under unfavorable conditions. Ribosome dimer formation strongly depends on the dimerization of the C-terminal domain of SaHPF (CTDSaHPF). In this study, we solved the crystal structure of CTDSaHPF at 1.6 Šresolution and obtained a precise arrangement of the dimer interface. Residues Phe160, Val162, Thr171, Ile173, Tyr175, Ile185 andThr187 in the dimer interface of SaHPF protein were mutated and the effects were analyzed for the formation of 100S disomes of ribosomes isolated from S. aureus. It was shown that substitution of any of single residues Phe160, Val162, Ile173, Tyr175 and Ile185 in the SaHPF homodimer interface abolished the ribosome dimerization in vitro.

Backbone and side chain NMR assignments for the ribosome Elongation Factor P (EF-P) from Staphylococcus aureus.

Elongation Factor P (EF-P) is a 20.5 kDa protein that provides specialized translation of special stalling amino acid motifs. Proteins with stalling motifs are often involved in various processes, including stress resistance and virulence. Thus it has been shown that the virulent properties of microorganisms can be significantly reduced if the work of EF-P is disrupted. In order to elucidate the structure, dynamics and function of EF-P from Staphylococcus aureus (S. aureus), here we report backbone and side chains 1H, 13C and 15N chemical shift assignments of EF-P. Analysis of the backbone chemical shifts by TALOS+ suggests that EF-P contains 1 α-helix and 13 ß-strands (ß1-ß2-ß3-ß4-ß5-ß6-ß7-α1-ß8-ß9-ß10-ß11-ß12-ß13). The solution of the structure of this protein by NMR and X-ray diffraction analysis, as well as the structure of the ribosome complex by cryo-electron microscopy, will allow further screening of highly selective inhibitors of the translation of the pathogenic bacterium S. aureus. Here we report the almost complete 1H, 13C, 15N backbone and side chain NMR assignment of a 20.5 kDa EF-P.

Surface modification of ferritic steels using MEVVA and duoplasmatron ion sources.

Metal Vapor Vacuum Arc (MEVVA) ion source (IS) is a unique tool for production of high intensity metal ion beam that can be used for material surface modification. From the other hand, the duoplasmatron ion source provides the high intensity gas ion beams. The MEVVA and duoplasmatron IS developed in Institute for Theoretical and Experimental Physics were used for the reactor steel surface modification experiments. Response of ferritic-martensitic steel specimens on titanium and nitrogen ions implantation and consequent vacuum annealing was investigated. Increase in microhardness of near surface region of irradiated specimens was observed. Local chemical analysis shows atom mixing and redistribution in the implanted layer followed with formation of ultrafine precipitates after annealing.

Colorimetric Evaluation of the Viability of the Microalga Dunaliella Salina as a Test Tool for Nanomaterial Toxicity.

A diagnostic test system was developed to determine the toxicity of nanomaterials to the saltwater microalga Dunaliella salina through evaluation of cell death and changes in the culture growth rate at various toxicant concentrations, providing LC50 and other toxicological metrics. The viability of cells was shown to decrease with decreasing chlorophyll absorption of red light by damaged cells. This correlation was confirmed by independent fluorescence microscopic measurements of live and dead cells in the population. Two standard colorless pollutants, hydrogen peroxide and formaldehyde, were used to validate the colorimetric method. The method's performance is exemplified with three Ag-containing preparations (Ag nitrate, Ag proteinate, and 20-nm Ag nanoparticles) and with cetyltrimethylammonium bromide (CTAB) mixed with colloidal 15-nm Au and 20-nm Ag nanoparticles. The toxicity of the Ag-containing preparations to D. salina decreased in the order Ag nitrate ≥ Ag proteinate ≫ colloidal Ag. The toxicity of colloidal Au-CTAB mixtures was found to depend mostly on the content of free CTAB. The toxicity of colloidal Ag increased substantially in the presence of CTAB. The results suggest that our D. salina-based colorimetric test system can be used for simple and rapid preliminary screening of the toxicity of different nanomaterials.