Crystal structure of eosinophil cationic protein at 2.4 A resolution

Eosinophil cationic protein (ECP) is located in the matrix of the eosinophil's large specific granule and has marked toxicity for a variety of helminth parasites, hemoflagellates, bacteria, single-stranded RNA virus, and mammalian cells and tissues. It belongs to the bovine pancreatic ribonuclease A (RNase A) family and exhibits ribonucleolytic activity which is about 100-fold lower than that of a related eosinophil ribonuclease, the eosinophil-derived neurotoxin (EDN). The crystal structure of human ECP, determined at 2.4 A, is similar to that of RNase A and EDN. It reveals that residues Gln-14, His-15, Lys-38, Thr-42, and His-128 at the active site are conserved as in all other RNase A homologues. Nevertheless, evidence for considerable divergence of ECP is also implicit in the structure. Amino acid residues Arg-7, Trp-10, Asn-39, His-64, and His-82 appear to play a key part in the substrate specificity and low catalytic activity of ECP. The structure also shows how the cationic residues are distributed on the surface of the ECP molecule that may have implications for an understanding of the cytotoxicity of this enzyme.     

Alteration in the endogenous intestinal flora of Swiss Webster mice by experimental Angiostrongylus costaricensis infection

The association between worm infections and bacterial diseases has only recently been emphasized. This study examined the effect of experimental Angiostrongylus costaricensis infection on endogenous intestinal flora of Swiss Webster mice. Eight mice aging six weeks were selected for this experiment. Four were infected with A. costaricensis and the other four were used as controls. Twenty eight days after the worm infection, all mice in both groups were sacrificed and samples of the contents of the ileum and colon were obtained and cultured for aerobic and anaerobic bacteria. In the mice infected with A. costaricensis there was a significant increase in the number of bacteria of the endogenous intestinal flora, accompanied by a decrease in the number of Peptostreptococcus spp. This alteration in the intestinal flora of mice infected by the nematode may help to understand some bacterial infections described in humans.     

Influence of aquatic microbiota on the survival in water of the human and eel pathogen Vibrio vulnificus serovar E

The eel and human pathogen Vibrio vulnificus serovar E (biotype 2) is seldom isolated from natural waters, although it can survive in sterilized artificial seawater microcosms for years. The main objective of the present study was to investigate whether aquatic microbiota can limit its survival and recovery from water samples. A set of preliminary experiments of survival in microcosms containing natural seawater and water from eel farms showed that the persistence of this pathogen was mainly controlled by grazing, and secondarily by bacterial competition. The bacterial competition was further analysed in artificial seawater microcosms co-inoculated with selected virulent serovar E (VSE) strains and potential competitors. Competitors included V. vulnificus biotype 1 isolates and strains of selected species that can grow on the selective media designed for V. vulnificus isolation from water samples. Evidences of bacterial competition that was detrimental for VSE recovery were recorded. Thus, some species produced a deleterious effect on VSE strains under starvation, and others were able to use the resources more efficiently under nutrient input. These results suggest that an overgrowth of more efficient competitor bacteria in conventional media used for isolation of V. vulnificus could mask the recovery of VSE strains and explain the scarcity of reports on the isolation of this human and eel pathogen from natural waters.     

The DNA sequence of chromosome I of an African trypanosome: gene content,chromosome organisation,recombination and polymorphism

The African trypanosome, Trypanosoma brucei, causes sleeping sickness in humans in sub-Saharan Africa. Here we report the sequence and analysis of the 1.1 Mb chromosome I, which encodes approximately 400 predicted genes organised into directional clusters, of which more than 100 are located in the largest cluster of 250 kb. A 160-kb region consists primarily of three gene families of unknown function, one of which contains a hotspot for retroelement insertion. We also identify five novel gene families. Indeed, almost 20% of predicted genes are members of families. In some cases, tandemly arrayed genes are 99–100% identical, suggesting an active process of amplification and gene conversion. One end of the chromosome consists of a putative bloodstream-form variant surface glycoprotein (VSG) gene expression site that appears truncated and degenerate. The other chromosome end carries VSG and expression site-associated genes and pseudogenes over 50 kb of subtelomeric sequence where, unusually, the telomere-proximal VSG gene is oriented away from the telomere. Our analysis includes the cataloguing of minor genetic variations between the chromosome I homologues and an estimate of crossing-over frequency during genetic exchange. Genetic polymorphisms are exceptionally rare in sequences located within and around the strand-switches between several gene clusters.     

Resistance to extinction of low fitness virus subjected to plaque-to-plaque transfers: diversification by mutation clustering.

Plaque-to-plaque transfers of RNA viruses lead to accumulation of mutations and fitness decrease. To test whether continuing plaque-to-plaque transfers would lead to viral extinction, we have subjected several low fitness foot-and-mouth disease virus (FMDV) clones to up to 130 successive plaque transfers, and have analyzed the evolution of plaque titers and genomic nucleotide sequences. No case of viral extinction could be documented. Some low fitness clones that posses an internal poly(A) tract evaded extinction by modifying the length or base composition of the poly(A) tract. The comparison of entire genomic sequences of FMDV clones at increasing plaque transfer number revealed that mutations accumulated at a uniform rate, and that they were distributed unevenly along the genome. Clusters of mutations were identified at different genomic sites in two plaque transfer lineages. Mutation clustering appears to occur stochastically and could not be related to fixation of compensatory mutations. The results document resistance of viral clones to extinction, and suggest that mutation clustering may be a mechanism of genetic diversification of low fitness virus.     

Tailoring of physical and chemical properties of macro- and microhydrogels based on telechelic PVA

Poly(vinyl alcohol), PVA, is amenable to several structural modifications because of the presence of the hydroxyl moiety in the backbone. The chemical versatility of this polymer can be used for the obtainment of new wall-to-wall pH-responsive PVA chemical hydrogels and for the preparation of air-filled microspheres, for example, microbubbles. Here, we report on the characterization of the physical and chemical properties of these novel networks that can be potentially used in different biomedical applications as controlled drug delivery and as ultrasonic contrast agent.