Presenilin-dependent intramembrane proteolysis of CD44 leads to the liberation of its intracellular domain and the secretion of an Abeta-like peptide

Alzheimer's disease (AD)-associated gamma-secretase is a presenilin (PS)- dependent proteolytic activity involved in the intramembraneous cleavage of the beta-amyloid precursor protein, Notch, LDL receptor-related protein, E-cadherin, and ErbB-4. This cut produces the corresponding intracellular domains (ICD), which are required for nuclear signaling of Notch and probably ErbB-4, the beta-amyloid precursor protein, E-cadherin, and the LDL receptor-related protein as well. We have now investigated CD44, a cell surface adhesion molecule, which also undergoes an intramembraneous cleavage to liberate its ICD. We demonstrate that this cleavage requires a PS-dependent gamma-secretase activity. A loss-of-function PS1 mutation, a PS1/PS2 knockout, as well as two independent and highly specific gamma-secretase inhibitors, abolish this cleavage. Surprisingly, small peptides similar to the amyloid beta-peptide (Abeta) are generated by an additional cut in the middle of the transmembrane region of CD44. Like Abeta, these CD44 beta-peptides are generated in a PS-dependent manner. These findings therefore suggest a dual intramembraneous cleavage mechanism mediated by PS proteins. The dual cleavage mechanism is required for nuclear signaling as well as removal of remaining transmembrane domains, a general function of PS in membrane protein metabolism.     

Evolutionary history and phylogeography of the schistosome-vector freshwater snail Biomphalaria glabrata based on nuclear and mitochondrial DNA sequences

The phylogeography of the freshwater snail Biomphalaria glabrata remains poorly known, although this species is the major vector of schistosomiasis in the New World. It was here investigated in South America and the Lesser Antilles, based on partial mitochondrial large ribosomal subunit (16S rDNA) and nuclear internal transcribed spacer-2 (ITS-2) gene sequences. Sampling included 17 populations from a large part of the current geographic range of the species (Brazil, Venezuela and Lesser Antilles). Substantial variability was detected, as well as a high amount of phylogenetically informative signal. The molecular phylogeny inferred splits B. glabrata into Northern and Southern clades separated by the Amazon river, and may even suggest a supra-specific status for B. glabrata. Brazilian populations were the most diverse and appeared basal to the other populations. Venezuelan haplotypes formed a single clade, albeit not strongly supported. Two Venezuelan haplotypes appear rather similar to Brazilian haplotypes. Similarly, Lesser Antilles haplotypes clustered in the same monophyletic clade, which suggests that the recent colonisation of the Antilles has a northern South American origin. However, the estimated divergence time between Antilles and Venezuelan sequences is extremely large (conservatively higher than 10(5) years). These results are discussed in the light of (i) phylogeographic patterns at South American scale, and (ii) recurrent introduction of molluscs, especially in the Antilles, as a consequence of human activities.     

Microbial growth in saline breast implants and saline tissue expanders

The subject of microbial growth within the saline medium of prosthetic breast implants has been one of great controversy in recent years. Although several articles have described microbial growth within the tissue surrounding implanted breast prostheses, few have attempted to determine the possibility of such contamination of the luminal saline. The authors studied the intraluminal saline medium of a series of explanted breast prostheses with the objective of identifying any microbial contamination. Over a 6-month period, a consecutive series of saline-filled breast implants and tissue expanders were removed from 37 patients. Under the supervision of a microbiologist, saline extracted from each implant was subjected to bacterial and fungal cultures, Gram staining, and acid-fast staining. A total of 24 saline-filled breast implants were removed from 15 patients, and 32 saline-filled tissue expanders were removed from 22 patients. The average length of implantation was 28.1 months for the implants and 7.1 months for the expanders. None of the saline within the implants or expanders within our series displayed any evidence of microbial contamination. These results suggest that microbial contamination of the luminal saline of prosthetic breast implants is an extremely unlikely event.     

Potential applications and pitfalls of Bayesian inference of phylogeny

Only recently has Bayesian inference of phylogeny been proposed. The method is now a practical alternative to the other methods; indeed, the method appears to possess advantages over the other methods in terms of ability to use complex models of evolution, ease of interpretation of the results, and computational efficiency. However, the method should be used cautiously. The results of a Bayesian analysis should be examined with respect to the sensitivity of the results to the priors used and the reliability of the Markov chain Monte Carlo approximation of the probabilities of trees.     

Density and diversity of protozoa in some arid Australian soils

This is the first extensive study of soil protozoa of arid lands. Twenty-six samples from litters, soils, termitaria, and a cyanobacterial crust, collected from central and south Australian arid lands, were analyzed for numbers and species of gymnamoebae, ciliates, and testacea. Amoebae ranged from 1,000-5,000/g of material, and were two orders of magnitude more abundant than ciliates. Both groups increased in abundance and species richness from bare soils through spinifex to mulga to chenopod vegetations. Testacea ranged 900-5,000/g with similar species richness throughout vegetations, but reached 11,900/g with a doubling of species in a refugium in Kings Canyon. The most prevalent species of amoebae, ciliates, and testacea were taxa associated with ephemeral and disturbed habitats (r-selection). The cyanobacterial crust might be considered a micro-refugium because it contained a number of non-encysting protozoa, including Thecamoeba sp. and Nassula picta, feeding on cyanobacterial filaments. The numbers and species richness of protozoa under shrubs were greater than in bare soils, supporting the resource island hypothesis that desert plants create soil heterogeneity by localizing soil fertility under their canopies.     

Hydrogen bonds from water molecules to aromatic acceptors in very high-resolution protein crystal structures

Short contacts of water molecules with the pi-faces of aromatic residues were studied in a set of 75 very high resolution (<1.1 A) protein X-ray crystal structures. For 18 water molecules found at distances to aromatic midpoints <3.5 A, it was attempted to assign the hydrogen bond configuration (without experimental knowledge of the H-atom positions) by inspection of the surrounding. For approximately one-quarter of the cases, evidence for an O-H...pi hydrogen bond was found, another one-quarter does not form such a hydrogen bond, and for the remaining half, no conclusive assignment could be made. The results confirm the relatively frequent occurrence of aromatic hydrogen bonding in biomolecular hydration, but also underline difficulties in hydrogen bond assignment without reliable knowledge of the H-atom positions.     

A novel beta-diketone-cleaving enzyme from Acinetobacter johnsonii: acetylacetone 2,3-oxygenase

A novel Fe+Zn containing oxygenase from Acinetobacter johnsonii catalyses 2,3-cleavage of acetylacetone to acetate and methylglyoxal has been purified. The stoichiometry of reactants and products conforms to a classical dioxygenase. The pure protein is a homotetramer of 64kD with variable amounts of Fe(2+) and Zn(2+). Activity of the enzyme is more closely related to the Fe(2+) content than to the amount of protein. A purification of acetylacetone 2,3-oxygenase, some of its physical properties, and the preference for some analogous substrates are described.     

Two nonadjacent regions in enteroaggregative Escherichia coli flagellin are required for activation of toll-like receptor 5

Flagellin is the major structural protein of the flagella of Gram-negative bacteria. Recent work has demonstrated that flagellin is a potent trigger of innate immune responses in a number of eukaryotic cells and organisms, including both mammals and plants. In several different human epithelial cell lines, this innate immune response involves toll-like receptor 5 (TLR5). The mechanisms by which flagellin activates TLR5 and the importance of this interaction in other model systems of flagellin-induced inflammation remain unknown. In this work, random and site-directed mutagenesis of the inflammatory flagellin from enteroaggregative Escherichia coli identified two regions in the conserved D1 domain that are required for interleukin-8 release and TLR5 activation. In contrast, large regions of the variable domain could be excised without reducing the inflammatory activity. In addition, regions of the protein analogous to epitopes that trigger innate immune responses in plants are not involved in Caco-2 flagellin responses. These results highlight the complexity of the interaction between bacterial flagellin and its eukaryotic recognition partners and provide the basis for further studies to characterize the innate immune response to flagellin.