Regulatory Interactions between a Bacterial Tyrosine Kinase and Its Cognate Phosphatase

The cyclic process of autophosphorylation of the C-terminal tyrosine cluster (YC) of a bacterial tyrosine kinase and its subsequent dephosphorylation following interactions with a counteracting tyrosine phosphatase regulates diverse physiological processes, including the biosynthesis and export of polysaccharides responsible for the formation of biofilms or virulence-determining capsules. We provide here the first detailed insight into this hitherto uncharacterized regulatory interaction at residue-specific resolution using Escherichia coli Wzc, a canonical bacterial tyrosine kinase, and its opposing tyrosine phosphatase, Wzb. The phosphatase Wzb utilizes a surface distal to the catalytic elements of the kinase, Wzc, to dock onto its catalytic domain (Wzc_CD). Wzc_CD binds in a largely YC-independent fashion near the Wzb catalytic site, inducing allosteric changes therein. YC dephosphorylation is proximity-mediated and reliant on the elevated concentration of phosphorylated YC near the Wzb active site resulting from Wzc_CD docking. Wzb principally recognizes the phosphate of its phosphotyrosine substrate and further stabilizes the tyrosine moiety through ring stacking interactions with a conserved active site tyrosine.     

The Combinatorial PP1-Binding Consensus Motif (R/K)x (0,1)V/IxFxx(R/K)x(R/K) Is a New Apoptotic Signature

Background

Previous studies established that PP1 is a target for Bcl-2 proteins and an important regulator of apoptosis. The two distinct functional PP1 consensus docking motifs, R/Kx_(0,1)V/IxF and FxxR/KxR/K, involved in PP1 binding and cell death were previously characterized in the BH1 and BH3 domains of some Bcl-2 proteins.

Principal Findings

In this study, we demonstrate that DPT-AIF₁, a peptide containing the AIF_562–571 sequence located in a c-terminal domain of AIF, is a new PP1 interacting and cell penetrating molecule. We also showed that DPT-AIF₁ provoked apoptosis in several human cell lines. Furthermore, DPT-APAF₁ a bi-partite cell penetrating peptide containing APAF-1_122–131, a non penetrating sequence from APAF-1 protein, linked to our previously described DPT-sh1 peptide shuttle, is also a PP1-interacting death molecule. Both AIF_562–571 and APAF-1_122–131 sequences contain a common R/Kx_(0,1)V/IxFxxR/KxR/K motif, shared by several proteins involved in control of cell survival pathways. This motif combines the two distinct PP1c consensus docking motifs initially identified in some Bcl-2 proteins. Interestingly DPT-AIF₂ and DPT-APAF₂ that carry a F to A mutation within this combinatorial motif, no longer exhibited any PP1c binding or apoptotic effects. Moreover the F to A mutation in DPT-AIF₂ also suppressed cell penetration.

Conclusion

These results indicate that the combinatorial PP1c docking motif R/Kx_(0,1)V/IxFxxR/KxR/K, deduced from AIF_562–571 and APAF-1_122–131 sequences, is a new PP1c-dependent Apoptotic Signature. This motif is also a new tool for drug design that could be used to characterize potential anti-tumour molecules.     

Convergent evolution of weakly electric fishes from floodplain habitats in Africa and South America

An assemblage of seven gymnotiform fishes in Venezuela was compared with an assemblage of six mormyriform fishes in Zambia to test the assumption of convergent evolution in the two groups of very distantly related, weakly electric, noctournal fishes. Both assemblages occur in strongly seasonal floodplain habitats, but the upper Zambezi floodplain in Zambia covers a much larger area. The two assemblages had broad diet overlap but relatively narrow overlap of morphological attributes associated with feeding. The gymnotiform assemblage had greater morphological variation, but mormyriforms had more dietary variation. There was ample evidence of evolutionary convergence based on both morphology and diet, and this was despite the fact that species pairwise morphological similarity and dietary similarity were uncorrelated in this dataset. For the most part, the two groups have diversified in a convergent fashion within the confines of their broader niche as nocturnal invertebrate feeders. Both assemblages contain midwater planktivores, microphagous vegetation-dwellers, macrophagous benthic foragers, and long-snouted benthic probers. The gymnotiform assemblage has one piscivore, a niche not represented in the upper Zambezi mormyriform assemblage, but present in the form of Mormyrops deliciousus in the lower Zambezi and many other regions of Africa.     

Glycosidases of apple fruit: A multi-functional β-galactosidase

Extraction of Spartan apple ( Malus domestica ) fruit acetone powder and fractionation of the extract on DEAE-agarose allowed detection and quantification of 10 glycosidases active toward 4-methylumbelliferyl glycosides. Hydrolysis was measured fluorimetrically. The predominant activity, a β- d -galactosidase (EC 3.2.1.23), labile upon purification, was stabilized by soluble PVP. Molecular weights, measured by gel permeation HPLC, pH optima and K_m values were obtained for most glycosidase activities. Multiple forms of several activities were found. The major α- d - and β- d -galactosidases were resolved on phosphocellulose. The β- d -galactosidase so obtained had associated α- l -arabinopyranosidase and β- d -fucosidase activities which were retained upon GP-HPLC. Mixed substrate kinetic analysis and inhibition analysis of this fraction indicated that the enzyme has 3 catalytic sites, 1 for each substrate, whose substrates mutually influence each other's activity positively.     

Septal apertures in the humerus of normal and experimental rats

Septal apertures of the humerus are rare in wild and domesticated rats but their occurrence is more frequent in females than in males and on the left than on the right side. Septal apertures can be produced experimentally by hypophysectomy due to an extreme reduction of the thickness of the septal wall. Other endocrine ablations, starvation and unilateral front leg paralysis do not produce a sufficient reduction of septal wall thickness to cause septal apertures. Their occurrence is also not correlated with total humeral robusticity. Thus, the manifestations of septal apertures in a non-specialized mammal such as the rat do not differ from those in higher primates.     

Gender and HIV-associated pulmonary tuberculosis: presentation and outcome at one year after beginning antituberculosis treatment in Uganda

Background  

Tuberculosis is responsible for more female deaths around the earth than any other infectious disease. Reports have suggested that responses to tuberculosis may differ between men and women. We investigated gender related differences in the presentation and one year outcomes of HIV-infected adults with initial episodes of pulmonary tuberculosis in Uganda.     

The assembly mode of the pseudopilus: a hallmark to distinguish a novel secretion system subtype

In gram-negative bacteria, type II secretion systems assemble a piston-like structure, called pseudopilus, which expels exoproteins out of the cell. The pseudopilus is constituted by a major pseudopilin that when overproduced multimerizes into a long cell surface structure named hyper-pseudopilus. Pseudomonas aeruginosa possesses two type II secretion systems, Xcp and Hxc. Although major pseudopilins are exchangeable among type II secretion systems, we show that XcpT and HxcT are not. We demonstrate that HxcT does not form a hyper-pseudopilus and is different in amino acid sequence and multimerization properties. Using structure-based mutagenesis, we observe that five mutations are sufficient to revert HxcT into a functional XcpT-like protein, which also becomes capable of forming a hyper-pseudopilus. Phylogenetic and experimental analysis showed that the whole Hxc system was acquired by P. aeruginosa PAO1 and other Pseudomonas species through horizontal gene transfer. We thus identified a new type II secretion subfamily, of which the P. aeruginosa Hxc system is the archetype. This finding demonstrates how similar bacterial machineries evolve toward distinct mechanisms that may contribute specific functions.     

Malaria Morbidity in High and Seasonal Malaria Transmission Area of Burkina Faso

Background

Malariometric parameters are often primary endpoints of efficacy trials of malaria vaccine candidates. This study aims to describe the epidemiology of malaria prior to the conduct of a series of drug and vaccine trials in a rural area of Burkina Faso.

Methods

Malaria incidence was prospectively evaluated over one year follow-up among two cohorts of children aged 0–5 years living in the Saponé health district. The parents of 1089 children comprising a passive case detection cohort were encouraged to seek care from the local health clinic at any time their child felt sick. Among this cohort, 555 children were randomly selected for inclusion in an active surveillance sub-cohort evaluated for clinical malaria during twice weekly home visits. Malaria prevalence was evaluated by cross-sectional survey during the low and high transmission seasons.

Results

Number of episodes per child ranged from 0 to 6 per year. Cumulative incidence was 67.4% in the passive and 86.2% in the active cohort and was highest among children 0–1 years. Clinical malaria prevalence was 9.8% in the low and 13.0% in the high season (p>0.05). Median days to first malaria episode ranged from 187 (95% CI 180–193) among children 0–1 years to 228 (95% CI 212, 242) among children 4–5 years. The alternative parasite thresholds for the malaria case definition that achieved optimal sensitivity and specificity (70–80%) were 3150 parasites/µl in the high and 1350 parasites/µl in the low season.

Conclusion

Clinical malaria burden was highest among the youngest age group children, who may represent the most appropriate target population for malaria vaccine candidate development. The pyrogenic threshold of parasitaemia varied markedly by season, suggesting a value for alternative parasitaemia levels in the malaria case defintion. Regional epidemiology of malaria described, Sapone area field centers are positioned for future conduct of malaria vaccine trials.