Deletion analysis of the FliM flagellar switch protein of Salmonella typhimurium.

The flagellar switch of Salmonella typhimurium and Escherichia coli is composed of three proteins, FliG, FliM, and FliN. The switch complex modulates the direction of flagellar motor rotation in response to information about the environment received through the chemotaxis signal transduction pathway. In particular, chemotaxis protein CheY is believed to bind to switch protein FliM, inducing clockwise filament rotation and tumbling. To investigate the function of FliM and its interactions with FliG and FliN, we engineered a series of 34 FliM deletion mutant proteins, each lacking a different 10-amino-acid segment. We have determined the phenotype associated with each mutant protein, the ability of each mutant protein to interfere with the motility of wild-type cells, and the effect of additional FliG and FliN on the function of selected FliM mutant proteins. Overall, deletions at the N terminus produced a counterclockwise switch bias, deletions in the central region of the protein produced poorly motile or nonflagellate cells, and deletions near the C terminus produced only nonflagellate cells. On the basis of this evidence and the results of a previous study of spontaneous FliM mutants (H. Sockett, S. Yamaguchi, M. Kihara, V. M. Irikura, and R. M. Macnab, J. Bacteriol. 174:793-806, 1992), we propose a division of the FliM protein into four functional regions: an N-terminal region primarily involved in switching, an extended N-terminal region involved in switching and assembly, a middle region involved in switching and motor rotation, and a C-terminal region primarily involved in flagellar assembly.     

Comparison of ITO and ZnO ternary glassy composites in terms of radiation shielding properties by Monte Carlo N-particle transport code and BXCOM

In the present study, radiation shielding properties of two glassy composite materials that are widely used in electronics, photovoltaic applications, and sensor technology, were investigated in the photon energy range from 15 keV to 15 MeV. The materials chosen were (ITO)/V2O5/B2O3 and ZnO/V2O5/B2O3 including various concentrations of B2O3. Radiation interaction was simulated and shielding parameters calculated by means of the MCNP and BXCOM codes. More specifically, buildup factors, effective electron density ($$N_{\text{eff}}$$) and effective atomic number ($$Z_{\text{eff}}$$) were calculated with BXCOM, while mass attenuation coefficients ($$\mu /\rho$$), half-value layer (HVL) and tenth-value layer (TVL) values were calculated with MCNP. The results were compared with those obtained with the WinXCOM code, for validation. Acceptable and preferable results were obtained for both composites as alternative to other glassy shielding materials. The composite including ITO showed better shielding properties than the composite including ZnO. In terms of radiation shielding, both composites turned out to be better than concrete and close to lead.     

Phosphorylation of the activation loop of gamma p21-activated kinase (gamma-Pak) and related kinases (MSTs) in normal and stressed neutrophils

Neutrophils stimulated with a variety of chemoattractants exhibit a rapid activation of two p21-activated kinases (Paks) with molecular masses of approximately 63 and 69 kDa (gamma- and alpha-Pak). A number of in vitro studies suggest that modification of Thr(402) in the activation loop (AL) of gamma-Pak can play a critical role in the regulation of this kinase under certain circumstances. A phosphospecific Ab was generated to this region of Pak (pPak(AL)Ab). This Ab reacted with activated gamma- and alpha-Pak from fMLP-stimulated neutrophils that contain the sequence KRXT(P)XXGTP in their ALS: The rapid but transient activation of Paks in normal stimulated neutrophils coincided with phosphorylation and dephosphorylation at the ALs of these enzymes. In contrast, stressed cells exhibited a prolonged phosphorylation at Thr(402) in both intact gamma-Pak and a proteolytic fragment of this kinase. The pPak(AL)Ab also reacted with the mammalian sterile twenty-like kinases (MSTs) (members of the Pak family) in osmotically stressed neutrophils and neutrophils treated with certain apoptotic agents (i.e., tumor promoters that inhibit type 1 and 2A protein phosphatases) but not in normal fMLP-stimulated cells. Thus, our results indicate that the AL of gamma-Pak undergoes transient phosphorylation during normal neutrophil stimulation and chronic phosphorylation in stressed cells. In addition, we demonstrate that a number of MSTs are present in neutrophils and also undergo phosphorylation during stressful circumstances.     

Role of superoxide dismutases (SODs) in controlling oxidative stress in plants

Reactive O(2) species (ROS) are produced in both unstressed and stressed cells. Plants have well-developed defence systems against ROS, involving both limiting the formation of ROS as well as instituting its removal. Under unstressed conditions, the formation and removal of O(2) are in balance. However, the defence system, when presented with increased ROS formation under stress conditions, can be overwhelmed. Within a cell, the superoxide dismutases (SODs) constitute the first line of defence against ROS. Specialization of function among the SODs may be due to a combination of the influence of subcellular location of the enzyme and upstream sequences in the genomic sequence. The commonality of elements in the upstream sequences of Fe, Mn and Cu/Zn SODs suggests a relatively recent origin for those regulatory regions. The differences in the upstream regions of the three FeSOD genes suggest differing regulatory control which is borne out in the research literature. The finding that the upstream sequences of Mn and peroxisomal Cu/Zn SODs have three common elements suggests a common regulatory pathway. The tools are available to dissect further the molecular basis for antioxidant defence responses in plant cells. SODs are clearly among the most important of those defences, when coupled with the necessary downstream events for full detoxification of ROS.     

Very low C-reactive protein in apparently healthy individuals: physiological status or just a reflection of an improved health profile

The objective of our study was to determine whether the very low concentrations of C-reactive protein (CRP) detected by high-sensitivity CRP (hs-CRP) assays that one encounters from time to time in apparently healthy individual represent a physiological status or are just a reflection of an improved general health profile. The concentration of hs-CRP was determined by using the Behring BN II nephelometer. The arbitrary cut-off point of hs-CRP (≤0.16mgl^-1) was determined at the lower detection level of the assay. A total of 6588 apparently healthy individuals were screened following exclusion of recent infection/inflammation by using a detailed questionnaire. One hundred and sixty (2.4%) individuals out of the above-mentioned cohort presented hs-CRP concentrations of ≤0.16mgl^-1. They were found to be significantly younger and lean, had an improved lipid profile and an attenuated acute-phase response in terms of lower erythrocyte sedimentation rate and fibrinogen concentration as well as white blood cell count. In addition, these individuals had less atherothrombotic risk factors, except for smoking habits which were as frequent as in those of individuals with a higher hs-CRP concentration. After calculating the concentration of this biomarker following multiple adjustments, the individuals with very low CRP remained with a very low value despite the multiplicity of the adjustments. We raise the possibility that this particular low concentration might represent a physiological status and is not necessarily a result of the improved general health profile per se.