Gating of acid-sensitive ion channel-1: release of Ca2+ block vs. allosteric mechanism

The acid-sensitive ion channels (ASICs) are a family of voltage-insensitive sodium channels activated by external protons. A previous study proposed that the mechanism underlying activation of ASIC consists of the removal of a Ca2+ ion from the channel pore (Immke and McCleskey, 2003). In this work we have revisited this issue by examining single channel recordings of ASIC1 from toadfish (fASIC1). We demonstrate that increases in the concentration of external protons or decreases in the concentration of external Ca2+ activate fASIC1 by progressively opening more channels and by increasing the rate of channel opening. Both maneuvers produced similar effects in channel kinetics, consistent with the former notion that protons displace a Ca2+ ion from a high-affinity binding site. However, we did not observe any of the predictions expected from the release of an open-channel blocker: decrease in the amplitude of the unitary currents, shortening of the mean open time, or a constant delay for the first opening when the concentration of external Ca2+ was decreased. Together, the results favor changes in allosteric conformations rather than unblocking of the pore as the mechanism gating fASIC1. At high concentrations, Ca2+ has an additional effect that consists of voltage-dependent decrease in the amplitude of unitary currents (EC50 of 10 mM at -60 mV and pH 6.0). This phenomenon is consistent with voltage-dependent block of the pore but it occurs at concentrations much higher than those required for gating.     

A new variety of Senna birostris (Leguminosae, Caesalpinioideae) from Argentina

Senna birostris previously included seven varieties distributed mostly above 2000 m, in the Andes, between the equator and 33°S. According to Irwin & Barneby,Senna birostris var.hookeriana was the only variety in Argentina, distributed from the Jujuy province to the San Luis province. New observations led us to identify two distinct entities that have gone under this taxon. The new variety,Senna birostris var.jallaguensis, is described from Argentina and illustrated herein and is compared toSenna birostris var.hookeriana s.str.     

Calcitonin forms oligomeric pore-like structures in lipid membranes

Calcitonin is a polypeptidic hormone involved in calcium metabolism in the bone. It belongs to the amyloid protein family, which is characterized by the common propensity to aggregate acquiring a beta-sheet conformation and include proteins associated with important neurodegenerative diseases. Here we show for the first time, to our knowledge, by transmission electron microscopy (TEM) that salmon-calcitonin (sCT) forms annular oligomers similar to those observed for beta-amyloid and alpha-sinuclein (Alzheimer's and Parkinson's diseases). We also investigated the interaction between sCT and model membranes, such as liposomes, with particular attention to the effect induced by lipid "rafts" made of cholesterol and G(M1). We observed, by TEM immunogold labeling of sCT, that protein binding is favored by the presence of rafts. In addition, we found by TEM that sCT oligomers inserted in the membrane have the characteristic pore-like morphology of the amyloid proteins. Circular dichroism experiments revealed an increase in beta-content in sCT secondary structure when the protein was reconstituted in rafts mimicking liposomes. Finally, we showed, by spectrofluorimetry experiments, that the presence of sCT allowed Ca(2+) entry in rafts mimicking liposomes loaded with the Ca(2+)-specific fluorophore Fluo-4. This demonstrates that sCT oligomers have ion-channel activity. Our results are in good agreement with recent electrophysiological studies reporting that sCT forms Ca(2+)-permeable ion channels in planar model membranes. It has been proposed that, beyond the well-known interaction of the monomer with the specific receptor, the formation of Ca(2+) channels due to sCT oligomers could represent an extra source of Ca(2+) entry in osteoblasts. Structural and functional data reported here support this hypothesis.     

Entropic criteria for protein folding derived from recurrences: six residues patch as the basic protein word

Some research has suggested that patches of six constitute an important amino acid window length in proteins for conveying information. We present database evidence that supports this conjecture, as well as additional recurrence-based data that characterization and quantification of these words affect the folding/aggregation features of proteins. Other indirect evidence is presented and discussed.     

Sub-attomole oligonucleotide and p53 cDNA determinations via a high-resolution surface plasmon resonance combined with oligonucleotide-capped gold nanoparticle signal amplification

Oligonucleotide (ODN)-capped gold nanoparticles (Au-NPs) were used in a sandwich assay of ODN or polynucleotide by a flow injection surface plasmon resonance (SPR). A carboxylated dextran film was immobilized onto the SPR sensor surface to eliminate nonspecific adsorption of ODN-capped Au-NPs. The tandem use of signal amplification via the adlayer of the ODN-capped Au-NPs and the differential signal detection by the bicell detector on the SPR resulted in a remarkable DNA detection level. A 39-mer target at a quantity as low as 2.1 x 10(-20)mol, corresponding to 1.38 fM in a 15 microl solution, can be measured. To our knowledge, both the concentration and quantity detection levels are the lowest among all the gene analyses conducted with SPR to this point. The method is shown to be reproducible (relative standard deviation values <16%) and to possess high sequence specificity. It is also demonstrated to be viable for sequence-specific p53 cDNA analysis. The successful elimination of nonspecific adsorption of, and the signal amplification by, ODN-capped Au-NPs renders the SPR attractive for cases where the DNA concentration is extremely low and the sample availability is severely limited.     

Direct Molecular Approach to Monitoring Bacterial Colonization on Vacuum-Packaged Beef

Denaturing gradient gel electrophoresis allowed us to monitor total bacterial communities and to establish a pattern of succession between species in vacuum-packaged beef stored at 2 and 8°C for 9 weeks and 14 days. Species-specific PCR was used to confirm the presence of Lactobacillus sakei and Lactobacillus curvatus. Multiplex PCRs using 16S rRNA-specific primers allowed differentiation between Leuconostoc species. These methods provided the desired information about microbial diversity by detecting the main microorganisms capable of colonizing this ecological niche.     

Blooms of Single Bacterial Species in a Coastal Lagoon of the Southwestern Atlantic Ocean

We investigated seasonal differences in community structure and activity (leucine incorporation) of the planktonic bacterial assemblage in the freshwater and brackish-water zones of a shallow coastal lagoon of the southwestern Atlantic Ocean. Alphaproteobacteria formed the dominant microbial group in both zones throughout the sampling period. After an intrusion of marine water, members of the SAR11 lineage became abundant in the brackish-water zone. These bacteria were apparently distributed over the lagoon during the following months until they constituted almost 30% of all prokaryotic cells at both sampling sites. At the first sampling date (March 2003) a single alphaproteobacterial species unrelated to SAR11, Sphingomonas echinoides, dominated the microbial assemblages in both zones of the lagoon concomitantly with a bloom of filamentous cyanobacteria. Pronounced maxima of leucine incorporation were observed once in each zone of the lagoon. In the freshwater zone, this highly active microbial assemblage was a mix of the typical bacteria lineages expected in aquatic systems. By contrast, a single bacterial genotype with >99% similarity to the facultative pathogen gammaproteobacterial species Stenotrophomonas maltophilia formed >90% of the bacterial assemblage (>10⁷ cell ml⁻¹) in the brackish-water zone at the time point of highest bacterial leucine incorporation. Moreover, these bacteria were equally dominant, albeit less active, in the freshwater zone. Thus, the pelagic zone of the studied lagoon harbored repeated short-term blooms of single bacterial species. This finding may have consequences for environmental protection.     

PSORS2 markers are not associated with psoriatic arthritis in the Italian population

Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy characterized by the association of arthritis and psoriasis (Ps). The precise etiology of PsA is unknown, but epidemiological studies supported the existence of a genetic component for the disease. Here we report an association study on a large PsA Italian cohort for DNA variants recently reported as associated alleles at PSORS2 (17q25) in Ps cohorts from the US. We focused on discovering a possible involvement of PSORS2 associated SNPs in pathogenesis of PsA. We selected two SNPs (rs7420, rs734232) within the proximal peak and two SNPs (rs869190 and rs1561946) within distal peak of PSORS2. Our results ruled out PSORS2 alleles as susceptibility factors in arthritis psoriatic patients of Italian origin and suggested that previous linkage signal reported for chromosome 17q25 should be independent on the presence of PsA.