Global assessment of nitrogen deposition effects on terrestrial plant diversity: a synthesis

Atmospheric nitrogen (N) deposition is a recognized threat to plant diversity in temperate and northern parts of Europe and North America. This paper assesses evidence from field experiments for N deposition effects and thresholds for terrestrial plant diversity protection across a latitudinal range of main categories of ecosystems, from arctic and boreal systems to tropical forests. Current thinking on the mechanisms of N deposition effects on plant diversity, the global distribution of G200 ecoregions, and current and future (2030) estimates of atmospheric N-deposition rates are then used to identify the risks to plant diversity in all major ecosystem types now and in the future. This synthesis paper clearly shows that N accumulation is the main driver of changes to species composition across the whole range of different ecosystem types by driving the competitive interactions that lead to composition change and/or making conditions unfavorable for some species. Other effects such as direct toxicity of nitrogen gases and aerosols, long-term negative effects of increased ammonium and ammonia availability, soil-mediated effects of acidification, and secondary stress and disturbance are more ecosystem- and site-specific and often play a supporting role. N deposition effects in mediterranean ecosystems have now been identified, leading to a first estimate of an effect threshold. Importantly, ecosystems thought of as not N limited, such as tropical and subtropical systems, may be more vulnerable in the regeneration phase, in situations where heterogeneity in N availability is reduced by atmospheric N deposition, on sandy soils, or in montane areas. Critical loads are effect thresholds for N deposition, and the critical load concept has helped European governments make progress toward reducing N loads on sensitive ecosystems. More needs to be done in Europe and North America, especially for the more sensitive ecosystem types, including several ecosystems of high conservation importance. The results of this assessment show that the vulnerable regions outside Europe and North America which have not received enough attention are ecoregions in eastern and southern Asia (China, India), an important part of the mediterranean ecoregion (California, southern Europe), and in the coming decades several subtropical and tropical parts of Latin America and Africa. Reductions in plant diversity by increased atmospheric N deposition may be more widespread than first thought, and more targeted studies are required in low background areas, especially in the G200 ecoregions.

The specificity of binding of glycoprotein hormones to their receptors

The glycoprotein hormone receptor family is peculiar because, in contrast to other G protein-coupled receptors, a large N-terminal extracellular ectodomain is responsible for hormone recognition. Hormone-receptor pairs have evolved in such a manner that a limited number of positions both at the 'seat-belt' domain of the hormone and the leucine-rich repeats of the receptor, play attractive and repulsive interactions for binding and specificity, respectively. Surprisingly, the constitutive activity of the receptor, mostly modulated by highly conserved amino acids within the heptahelical domain of the receptor (i.e., outside the hormone binding region), also regulates effectiveness of hormone recognition by the extracellular part. In this review we analyze, at the molecular level, these important discriminating determinants for selective binding of glycoprotein hormones to their receptors, as well as natural mutations, observed in patients with gestational hyperthyroidism or ovarian hyperstimulation syndrome, that modify the selectivity of binding.

[Detection and characterization of Shiga toxin-producing Escherichia coli from clinical cases and food in Uruguay]

We have assessed the frequency of Shiga toxin-producing Escherichia coil (STEC) in clinical and food samples as well as studied the genotypic and phenotypic characteristics of the recovered strains. One hundred ninety eight fecal samples from children with bloody diarrhea (BD), 14 from children with hemolytic uremic syndrome (HUS), 220 ground beef samples and 4 STEC isolates from other beef-derived products were analyzed. The STEC strains were isolated from 3 (1.5%) children with bloody diarrhea, 1 (7%) from a child with HUS and 4 (1.8%) from ground beef samples. All strains were eae and ehxA positive. The serotypes found were: O157:H7 (9 strains), O26:H11 (2), O111: NM (1) and O145:HNT (1). All O157:H7 STEC strains harbored the eae subtype gamma1, O26:H11 and O145:HNT strains, subtype beta1 and O111:NM strain, subtype gamma2/theta. The STEC strains of the same serogroup showed high genetic diversity. In Uruguay, STEC is not frequently isolated from cases of bloody diarrhea in children. However, all the recovered STEC strains carried the genes associated with severe disease and 2 out of 3 children infected with STEC developed HUS. Ground beef and other food products might be important vehicles for O157:H7 strains.

Order-restricted Dose-related Trend Phi-divergence Tests for Generalized Linear Models

In this paper a new family of test statistics is presented for testing the independence between the binary response Y and an ordered categorical explanatory variable X (doses) against the alternative hypothesis of an increase dose-response relationship between a response variable Y and X (doses). The properties of these test statistics are studied. This new family of test statistics is based on the family of φ-divergence measures and contains as a particular case the likelihood ratio test. We pay special attention to the family of test statistics associated with the power divergence family. A simulation study is included in order to analyze the behavior of the power divergence family of test statistics.

Structure-based secondary structure-independent approach to design protein ligands: Application to the design of Kv1.2 potassium channel blockers

We have developed a structure-based approach to the design of protein ligands. This approach is based on the transfer of a functional binding motif of amino acids, often referred as to the "hot spot", on a host protein able to reproduce the functional topology of these residues. The scaffolds were identified by a systematic in silico search in the Protein Data Bank for proteins possessing a group of residues in a topology similar to that adopted by the functional motif in a reference ligand of known 3D structure. In contrast to previously reported studies, this search is independent of the particular secondary structure supporting the functional motif. To take into account the global properties of the host protein, two additional criteria were taken into account in the selection process: (1) Only those scaffolds sterically compatible with the positioning of the functional motif as observed in a reference complex model were retained. (2) Host proteins displaying electrostatic potentials, in the region of the transferred functional motif, similar to that of the reference ligand were selected. This approach was applied to the development of protein ligands of the Kv1.2 channel using BgK, a small protein isolated from the sea anemone Bunodosoma granulifera, as the reference ligand. Four proteins obtained by this approach were produced for experimental evaluation. The X-ray structure of one of these proteins was determined to check for similarity of the transferred functional motif with the structure it adopts in the reference ligand. Three of these protein ligands bind the Kv1.2 channel with inhibition constants of 0.5, 1.5, and 1.6 microM. Several mutants of these designed protein ligands gave binding results consistent with the presumed binding mode. These results show that protein ligands can be designed by transferring a binding motif on a protein host selected to reproduce the functional topology of this motif, irrespective to the secondary structure supporting the functional motif, if the host protein possesses steric and electrostatic properties compatible with the binding to the target. This result opens the way to the design of protein ligands by taking advantage of the considerable structural repertoire of the Protein Data Bank.