Sensor domains encoded in Bacillus anthracis virulence plasmids prevent sporulation by hijacking a sporulation sensor histidine kinase

Anthrax toxin and capsule, determinants for successful infection by Bacillus anthracis, are encoded on the virulence plasmids pXO1 and pXO2, respectively. Each of these plasmids also encodes proteins that are highly homologous to the signal sensor domain of a chromosomally encoded major sporulation sensor histidine kinase (BA2291) in this organism. B. anthracis Sterne overexpressing the plasmid pXO2-61-encoded signal sensor domain exhibited a significant decrease in sporulation that was suppressed by the deletion of the BA2291 gene. Expression of the sensor domains from the pXO1-118 and pXO2-61 genes in Bacillus subtilis strains carrying the B. anthracis sporulation sensor kinase BA2291 gene resulted in BA2291-dependent inhibition of sporulation. These results indicate that sporulation sensor kinase BA2291 is converted from an activator to an inhibitor of sporulation in its native host by the virulence plasmid-encoded signal sensor domains. We speculate that activation of these signal sensor domains contributes to the initiation of B. anthracis sporulation in the bloodstream of its infected host, a salient characteristic in the virulence of this organism, and provides an additional role for the virulence plasmids in anthrax pathogenesis.     

Ligand scaffold hopping combining 3D maximal substructure search and molecular similarity

Background  

Virtual screening methods are now well established as effective to identify hit and lead candidates and are fully integrated in most drug discovery programs. Ligand-based approaches make use of physico-chemical, structural and energetics properties of known active compounds to search large chemical libraries for related and novel chemotypes. While 2D-similarity search tools are known to be fast and efficient, the use of 3D-similarity search methods can be very valuable to many research projects as integration of "3D knowledge" can facilitate the identification of not only related molecules but also of chemicals possessing distant scaffolds as compared to the query and therefore be more inclined to scaffolds hopping. To date, very few methods performing this task are easily available to the scientific community.     

Is a dietary n-3 fatty acid supplement able to influence the cardiac effect of the psychological stress?

Epidemiological studies suggest that n-3 polyunsaturated fatty acids (PUFA) are involved in the prevention of cardiovascular disease. Stress is known to increase the incidence of CVD and the present study was realised to evaluate some physiological and biochemical effects of dietary docosahexaenoic acid (DHA) in male Wistar rats subjected to a psycho social stress. Rats were fed for 8 weeks a semi-purified diet containing 10% of either sunflower seed oil or the same oil supplemented with DHA. This food supply represented 50% of their daily requirement. The remaining 50% were supplied as 45 mg food pellets designed to induce stress in rats by an intermittent-feeding schedule process. The control group (n = 12) was fed the equivalent food ration as a single daily feeding. The physiological cardiovascular parameters were recorded by telemetry through a transmitter introduced in the abdomen. At the end of the experimentation, the heart and adrenals were withdrawn and the fatty acid composition and the catecholamine store were determined. Dietary DHA induced a pronounced alteration of the fatty acid profile of cardiac phospholipids (PL). The level of all the n-6 PUFAs was reduced while 22:6 n-3 was increased. The stress induced a significant increase in heart rate which was not observed in DHA-fed group. The time evolution of the systolic blood pressure was not affected by the stress and was roughly similar in the stressed rats of either dietary group. Conversely, the systolic blood pressure decreased in the unstressed rats fed DHA. Similar data were obtained for the diastolic blood pressure. The beneficial effect of DHA was also observed on cardiac contractility, since the dP/dt_max increase was prevented in the DHA-fed rats. The stress-induced modifications were associated with an increase in cardiac noradrenaline level which was not observed in DHA-fed rats. The fatty acid composition of adrenals was significantly related to the fatty acid intake particularly the neutral lipid fraction (NL) which incorporated a large amount of DHA. Conversely, n-3 PUFAs were poorly incorporated in adrenal phospholipids. Moreover the NL/PL ratio was significantly increased in the DHA fed rats. The amount of adrenal catecholamines did not differ significantly between the groups. These results show that a supplementation of the diet with DHA induced cardiovascular alterations which could be detected in conscious animals within a few weeks. These alterations were elicited by a reduced heart rate and systolic and diastolic blood pressure.     

Regulation of intermediary metabolism in rat cardiac myocyte by extracellular glycerol

In the human heart, although all substrates compete for energy production, fatty acids (FA) represent the main substrate for ATP production. In the healthy heart, a balance between FA and carbohydrate utilization ensures that energy supply matches demand. This study was carried out to evaluate, in a model of spontaneously beating neonatal rat cardiomyocytes in culture, the hypothesis that glycerol could play a central role in the metabolic control of the routes involving long chain FAs and may then affect the balance between beta-oxidation and glucose oxidation. The intracellular-free glycerol significantly increased with extracellular glycerol concentration (0 to 660 microM). The synthesis of phospholipids was significantly increased in parallel with both extracellular glycerol (1.5 and 14.8 nmol glycerol/mg protein, at 82 and 660 microM of extracellular glycerol, respectively). The oxidation of glycerol increased proportionally to extracellular glycerol concentration (from 1 to 3 nmol glycerol/mg protein, at 82 microM and 660 microM extracellular glycerol, respectively, P<0.001). At its maximum, this oxidation represented 15% of the glucose oxidation, which was not affected by glycerol extracellular supply or intracellular availability. Conversely, extracellular glycerol significantly reduced the palmitate oxidation above (-47% at 660 microM glycerol), but not octanoate oxidation. Investigations on the mechanism of the decreased palmitate oxidation reveals a glycerol-dependent increase in malonyl-CoA associated with a significant decrease in CPT-1 activity which accounts for the difference between palmitate and octanoate. These results clearly demonstrate the importance of glycerol in regulating the cardiac metabolic pathways and energy balance.     

Docosahexaenoic acid affects insulin deficiency- and insulin resistance-induced alterations in cardiac mitochondria

The effect of docosahexaenoic acid (DHA) intake on cardiac mitochondrial function was evaluated in permeabilized fibers in insulin deficiency and insulin resistance in rats. The insulin-deficient state was obtained by streptozotocin injection 2 mo before investigations. Insulin resistance was obtained by feeding a 62% fructose diet for 3 mo. DHA was incorporated in the diet to modify the fatty acid composition of cardiac membranes, including mitochondria. Insulin deficiency decreased mitochondrial creatine kinase (mi-CK) activity and mitochondrial sensitivity to ADP. DHA intake prevented these alterations. Moreover, the insulin-deficient state significantly decreased n-3 polyunsaturated fatty acids (PUFA) and slightly increased n-6 PUFA in both cardiac and mitochondrial membranes, inducing a significant increase in the n-6-to-n-3 ratio. DHA intake maintained high myocardial and mitochondrial DHA content. Insulin deficiency also decreased glutamate- and palmitoylcarnitine-supported mitochondrial respiration, but DHA intake did not prevent these effects. In contrast, insulin resistance did not affect mi-CK activity or sensitivity to ADP. However, insulin resistance influenced the myocardial fatty acid composition with decreased n-6 and n-3 PUFA contents and increased monounsaturated fatty acid content. Only slight alterations were observed in mitochondrial fatty acid composition, and they were corrected by DHA intake. Moreover, insulin resistance decreased the glutamate-supported respiration, and DHA intake did not influence this effect. In conclusion, the impairment of cardiac mitochondrial function was more pronounced in the insulin-deficient state than in insulin resistance. The modification of fatty acid composition of cardiac and mitochondrial membranes by DHA partially prevented the mitochondrial alterations induced in the two models.     

HEPN: a common domain in bacterial drug resistance and human neurodegenerative proteins

A novel domain - HEPN (higher eukarytoes and prokaryotes nucleotide-binding domain) - found in several bacterial species is also present in the human protein, sacsin, a chaperonin implicated in an early-onset neurodegenerative disease. The distant structural similarity suggests that this domain might be involved in nucleotide binding.     

Proteomic Analysis of Trypanosoma cruzi Response to Ionizing Radiation Stress

Trypanosoma cruzi, the causative agent of Chagas disease, is extremely resistant to ionizing radiation, enduring up to 1.5 kGy of gamma rays. Ionizing radiation can damage the DNA molecule both directly, resulting in double-strand breaks, and indirectly, as a consequence of reactive oxygen species production. After a dose of 500 Gy of gamma rays, the parasite genome is fragmented, but the chromosomal bands are restored within 48 hours. Under such conditions, cell growth arrests for up to 120 hours and the parasites resume normal growth after this period. To better understand the parasite response to ionizing radiation, we analyzed the proteome of irradiated (4, 24, and 96 hours after irradiation) and non-irradiated T. cruzi using two-dimensional differential gel electrophoresis followed by mass spectrometry for protein identification. A total of 543 spots were found to be differentially expressed, from which 215 were identified. These identified protein spots represent different isoforms of only 53 proteins. We observed a tendency for overexpression of proteins with molecular weights below predicted, indicating that these may be processed, yielding shorter polypeptides. The presence of shorter protein isoforms after irradiation suggests the occurrence of post-translational modifications and/or processing in response to gamma radiation stress. Our results also indicate that active translation is essential for the recovery of parasites from ionizing radiation damage. This study therefore reveals the peculiar response of T. cruzi to ionizing radiation, raising questions about how this organism can change its protein expression to survive such a harmful stress.     

Polymorphism at the apical membrane antigen 1 locus reflects the world population history of <Emphasis Type="Italic">Plasmodium vivax</Emphasis>

Background  

In malaria parasites (genus Plasmodium), ama-1 is a highly polymorphic locus encoding the Apical Membrane Protein-1, and there is evidence that the polymorphism at this locus is selectively maintained. We tested the hypothesis that polymorphism at the ama-1 locus reflects population history in Plasmodium vivax, which is believed to have originated in Southeast Asia and is widely geographically distributed. In particular, we tested for a signature of the introduction of P. vivax into the New World at the time of the European conquest and African slave trade and subsequent population expansion.     

Influence of dietary linseed oil and sunflower seed oil on some mechanical and metabolic parameters of isolated working rat hearts

The role played by membrane lipid environment on cardiac function remains poorly defined. The polyunsaturated fatty acid profile of myocardial phospholipids could be of utmost importance in the regulation of key-enzyme activities. This study was undertaken to determine whether selective incorporation of n-6 or n-3 fatty acids in membrane phospholipids might influence cardiac mechanical performances and metabolism. For 8 wk, male weaning Wistar rats were fed a semi-purified diet containing either 10% sunflower seed oil (72% C18:2 n-6) or 10% linseed oil (54% C18:3 n-3) as the sole source of lipids. The hearts were then removed and perfused according to working mode with a Krebs-Henseleit buffer containing glucose (11 mM) and insulin (10 Ul/l). Cardiac rate, coronary and aortic flows and ejection fraction were monitored after 30 min of perfusion. Myocardial metabolism was estimated by evaluating the intracellular fate of 1-14C palmitate. Sunflower seed oil and linseed oil feeding did not modify either coronary or aortic flow, which suggests that cardiac mechanical work was not affected by the diets. Conversely, cardiac rate was significantly decreased (-18%; P less than 0.01) when rats were fed the n-3 polyunsaturated fatty acid rich diet. Radioanalysis of the myocardial metabolism suggested that replacing n-6 polyunsaturated fatty acids by n-3 polyunsaturated fatty acids: i) did not alter palmitate uptake; ii) prolonged palmitate incorporation into cardiac triglycerides; iii) reduced beta-oxidation of palmitic acid. These results support the assumption that dietary fatty acids, particularly n-6 and n-3 fatty acids, play an important role in the regulation of cardiac mechanical and metabolic activity.