Small-Angle x-ray scattering and crystallographic studies of arcelin-1: An insecticidal lectin-like glycoprotein from Phaseolus vulgaris L

Arcelin-1 and α-amylase inhibitor are two lectin-like glycoproteins expressed in the seeds of the kidney bean (Phaseolus vulgaris). They display insecticidal activities and protect the seeds from predation by larvae of various bruchids through different biological actions. Solution-state investigations by small-angle X-ray scattering (SAXS) show the dimeric structure of arcelin-1, a requirement for its hemagglutinating properties. Anions were found to have specific properties in their effectiveness to disrupt protein aggregates, affect solubility, and improve crystallizability. The SAXS results were used to improve crystallization conditions, and single crystals diffracting beyond 1.9 Å resolution were obtained. X-ray diffraction data analysis shows that noncrystallographic symmetry-related arcelin-1 molecules form a lectin-like dimer and reveals the presence of a solvent-exposed anion binding site on the protein, at a crystal-packing interface. The solution state properties of arcelin-1 and crystal twinning may be explained by the anion specificity of this binding site. Proteins 29:433–442, 1997. © 1997 Wiley-Liss, Inc.     

Amphioxus postembryonic development reveals the homology of chordate metamorphosis

Most studies in evolution are centered on how homologous genes, structures, and/or processes appeared and diverged. Although historical homology is well defined as a concept, in practice its establishment can be problematic, especially for some morphological traits or developmental processes. Metamorphosis in chordates is such an enigmatic character. Defined as a spectacular postembryonic larva-to-adult transition, it shows a wide morphological diversity between the different chordate lineages, suggesting that it might have appeared several times independently. In vertebrates, metamorphosis is triggered by binding of the thyroid hormones (THs) T(4) and T(3) to thyroid-hormone receptors (TRs). Here we show that a TH derivative, triiodothyroacetic acid (TRIAC), induces metamorphosis in the cephalochordate amphioxus. The amphioxus TR (amphiTR) mediates spontaneous and TRIAC-induced metamorphosis because it strongly binds to TRIAC, and a specific TR antagonist, NH3, inhibits both spontaneous and TRIAC-induced metamorphosis. Moreover, as in amphibians, amphiTR expression levels increase around metamorphosis and are enhanced by THs. Therefore, TH-regulated metamorphosis, mediated by TR, is an ancestral feature of all chordates. This conservation of a regulatory network supports the homology of metamorphosis in the chordate lineage.     

When leaves act like flowers: how dwarf palms attract their pollinators

In pollination mutualisms, floral odours are signals advertising the presence and location of rewards. However, in the case of the dwarf palm (Chamaerops humilis) and its species‐specific pollinating weevil (Derelomus chamaeropsis), rewards and advertisements are spatially separated. Flowers provide their specific pollinators with food and sites for both egg laying and larval development, but do not advertise them with floral odours or visually conspicuous petals. Insect behavioural bioassays revealed that pollinators are attracted by scents emitted by the leaves, which provide no rewards. These scents are released by large structures located at the sinuses of the palmate leaf. Such scent‐releasing structures have not been previously reported on palm leaves, and we suggest that they may represent an ‘exaptation’ (pre‐existing trait that acquired new functions). We also propose that such functional crossovers between vegetative and reproductive domains may be more frequent in plants than is currently documented.     

Characterization of a Highly Conserved Binding Site of Mlh1 Required for Exonuclease I-Dependent Mismatch Repair

Mlh1 is an essential factor of mismatch repair (MMR) and meiotic recombination. It interacts through its C-terminal region with MutL homologs and proteins involved in DNA repair and replication. In this study, we identified the site of yeast Mlh1 critical for the interaction with Exo1, Ntg2, and Sgs1 proteins, designated as site S2 by reference to the Mlh1/Pms1 heterodimerization site S1. We show that site S2 is also involved in the interaction between human MLH1 and EXO1 or BLM. Binding at this site involves a common motif on Mlh1 partners that we called the MIP-box for the Mlh1 interacting protein box. Direct and specific interactions between yeast Mlh1 and peptides derived from Exo1, Ntg2, and Sgs1 and between human MLH1 and peptide derived from EXO1 and BLM were measured with K_d values ranging from 8.1 to 17.4 μM. In Saccharomyces cerevisiae, a mutant of Mlh1 targeted at site S2 (Mlh1-E682A) behaves as a hypomorphic form of Exo1. The site S2 in Mlh1 mediates Exo1 recruitment in order to optimize MMR-dependent mutation avoidance. Given the conservation of Mlh1 and Exo1 interaction, it may readily impact Mlh1-dependent functions such as cancer prevention in higher eukaryotes.     

Prokaryotic aminopeptidase activity along a continuous salinity gradient in a hypersaline coastal lagoon (the Coorong, South Australia)

The relation between climatic parameters (relative air humidity) and the water activity of the Urmia Sea water determines the possible maximum evaporation of the lake. Using the Pitzer thermodynamic approach, the activity of the Urmia Lake water during evaporation was calculated and compared to the present relative air humidity above the water. Present climatic conditions allow the Urmia Sea water to evaporate down to water with activity of 0.55, corresponding to the lowest air humidity measured over the lake. This water activity falls in the range of halite precipitation, while carnalite precipitation starts at somewhat lower (a H₂O = 0.499) point. Our dynamic model predicts that for air humidity as low as 55% (reflecting present climate conditions), the Urmia Sea level may drop to as low as 1270 m (i. e., 1270 m above mean sea level). At that point, the lake water volume will have a volume of 11 km³. For the sake of comparison, at the beginning of 1990, the level of the lake was 1275 m, its volume was 25 km³, and its surface area was 5145 km².     

Immigrational Background Affects the Effectiveness of a School‐based Overweight Prevention Program Promoting Water Consumption

We tested whether a simple overweight prevention program promoting water consumption in elementary schools is equally effective in children with an immigrational background (MIG) and in those without (non‐MIG). Thus, a secondary analysis of a controlled cluster trial, lasting one school year, was conducted. Thirty‐two elementary schools located in low socioeconomic districts in two German cities were included. Of the 2,950 school children analyzed, 1,306 were MIG children. Water fountains were installed in the schools of the intervention group (IG) and teachers held lessons to promote water consumption. Control schools (control group (CG)) did not receive any intervention. Before and after intervention, body weight and height was measured. Overweight was defined by age‐ and sex‐specific BMI cutoffs that are linked to an adult BMI of 25 kg/m². Beverage consumption was assessed in questionnaires. Modification of intervention effects by immigrational background was tested by interaction terms. The immigrational background modified the intervention effect on prevalence and remission of overweight (interaction term: P = 0.03 and P = 0.02), but not on the incidence of overweight (P = 0.06). After intervention, the risk of being overweight was reduced in the IG compared to the CG among non‐MIG (odds ratio = 0.51, 95% confidence interval (CI): 0.31–0.83), but not among MIG children (odds ratio = 1.02, 95% CI: 0.63–1.65). After intervention, water consumption significantly increased in the IG equally among both, non‐MIG and MIG, by ～1 glass/day. A simple school‐based intervention promoting water consumption prevented overweight in non‐MIG children, but failed in MIG children. Different beverage consumption, among other lifestyle factors, may account for this effect but scientific discussion remains open.