Different duplex/quadruplex junctions determine the properties of anti-thrombin aptamers with mixed folding

Mixed duplex/quadruplex oligonucleotides have attracted great interest as therapeutic targets as well as effective biomedical aptamers. In the case of thrombin-binding aptamer (TBA), the addition of a duplex motif to the G-quadruplex module improves the aptamer resistance to biodegradation and the affinity for thrombin. In particular, the mixed oligonucleotide RE31 is significantly more effective than TBA in anticoagulation experiments and shows a slower disappearance rate in human plasma and blood. In the crystal structure of the complex with thrombin, RE31 adopts an elongated structure in which the duplex and quadruplex regions are perfectly stacked on top of each other, firmly connected by a well-structured junction. The lock-and-key shape complementarity between the TT loops of the G-quadruplex and the protein exosite I gives rise to the basic interaction that stabilizes the complex. However, our data suggest that the duplex motif may have an active role in determining the greater anti-thrombin activity in biological fluids with respect to TBA. This work gives new information on mixed oligonucleotides and highlights the importance of structural data on duplex/quadruplex junctions, which appear to be varied, unpredictable, and fundamental in determining the aptamer functional properties.     

Temporal genetic dynamics among mosquitofish (<Emphasis Type="Italic">Gambusia holbrooki</Emphasis>) populations in invaded watersheds

The temporal components of genetic diversity and geographical structure of invasive mosquitofish populations are poorly known. Through the genetic monitoring of four consecutive cohorts of Gambusia holbrooki from three different river basins we aimed to determine temporal patterns of regional genetic variation and dispersal rates within invasive populations. Despite showing evidence of strong population size fluctuations, genetic diversity levels were maintained among local cohorts. We only detected temporal allele frequency changes associated with seasonal flooding that did not modify major trends on population structure among cohorts. Downstream gene flow coupled with increased connectivity at lowland locations to increase genetic diversity levels in these areas. A large proportion of local fish (up to 50 %) were dispersers, often originated from locations within the same river basin. High dispersal capability, ecological tolerance, and reproductive traits likely promote river colonization. Finally, our results also confirmed that human-assisted translocations promote within and among basin gene flow and maintained levels of genetic diversity, particularly in upstream locations.     

Environmental assessment in an industrial area of Portugal

The region of Lisbon and south of Lisbon (Sado estuary) is densely industrialized, and, therefore, air pollution should be studied in a more detailed scale there. The topography of the Sado estuary region and the predominant wind direction from the northwest contribute to the influence in this region of the industries located in the north. The region selected includes a fuel-fired power station. Transplants of the lichenParmelia sulcata Taylor were suspended in nylon bags within a rectangle 15 km wide and 25 km long on a grid 2.5 km × 2.5 km, centered in the power station. In each of the 47 sites, 2 sets of 4 transplants each were hung. Care was taken (1) in covering the two sets with a polyethylene roof to prevent leaching of elements in the lichen, (2) in building a hanging system that could rotate according to the wind direction, and (3) in orienting one set toward the wind and the other set opposite the wind. For a 1-yr period and every 3 mo, one transplant of each set is collected. In this work, the results of the first campaign (after 3 mo suspension) obtained by instrumental neutron activation analysis and proton-induced X-ray emission are shown. Some elemental contents are mapped and discussed.     

Changes in the structure and the functional state of thylakoids under the conditions of osmotic shock

The effect of osmotic shock on the ultrastructure and functions of C-class pea chloroplasts has been examined. When incubated in a non-sucrose medium for 30 s or more, thylakoids were found to pass to a stable deformed state. This state was characterized by an altered orientation of thylakoids to each other with the lumen thickness remaining the same as in the normal state. Experiments with shorter incubation periods (10–20 s) revealed a swelling of thylakoids, which probably represented an intermediate stage. The deformation of the thylakoid system was accompanied by a decrease in the non-cyclic ATP synthesis but by an increase in the rate of cyclic photophosphorylation. Besides, the deformed thylakoids demonstrated an acceleration of the basal electron transport, as well a rise in the light-induced H⁺ and imidazol uptake. The data obtained are discussed in the light of membrane interactions fixing the configuration of a thylakoid.