María J. Prieto

Intramolecular DNA coiling mediated by metallo-supramolecular cylinders: Differential binding of P and M helical enantiomers

We have designed a synthetic tetracationic metallo-supramolecular cylinder that targets the major groove of DNA with a binding constant in excess of 107 M−1 and induces DNA bending and intramolecular coiling. The two enantiomers of the helical molecule bind differently to DNA and have different structural effects. We report the characterization of the interactions by a range of biophysical techniques. The M helical cylinder binds to the major groove and induces dramatic intramolecular coiling. The DNA bending is less dramatic for the P enantiomer.

The Gebra Slide: a submarine slide on the Trinity Peninsula Margin, Antarctica

A large submarine slide – the Gebra Slide – has been discovered on the continental margin of Trinity Peninsula, Central Bransfield Basin, Antarctic Peninsula. The slide scar is clearly expressed in the bathymetry and is cut into the toe of the glacial-period slope-prograding strata on the lower continental slope. Seismic data give evidence of an associated debris-flow deposit embedded in the interglacial-period basin-fill strata of the basin floor. The total volume of sediment involved in the mass movement is about 20 km3. Indirect dating of the mass-wasting event, based on seismic–stratigraphic relationships of the slide scar and associated debris-flow deposit with underlying glacial-period slope units and the overlying interglacial-period basin-floor units, suggests that it took place at the transition between the last glacial period and the present-day interglacial. The initiation of the Gebra Slide is attributed to a combination of several factors, such as high sedimentation rates during the last glacial period, the unloading effect of a retreating ice sheet during deglaciation, pre-existing tectonic fabric and high seismicity in the area. This is the first recent submarine slide of this size identified on the glacial, continental margins of Antarctica. In morphology and general characteristics it is quite similar to the well-known large-scale submarine slides from the northern hemisphere glacial margins, although it is smaller. Its most striking characteristic is its lower-slope position (at 1500–2000 m of water depth), which remains up to now difficult to explain.

Structure and geodynamic evolution of the central Bransfield Basin (NW Antarctica) from seismic reflection data.

Abstract The Bransfield Basin is a young active rift basin located between the northern margin of the Antarctic Peninsula and the South Shetland Islands margin. Deception and Bridgeman islands divide the Bransfield Basin in three subbasins, the western, central and eastern. Specific morpho-tectonic features and sediment fill differentiate each subbasin. The structure and geodynamic evolution of the Central Bransfield Basin, which is in a stage of incipient seafloor spreading, have been investigated in detail from a dense grid of single-channel seismic reflection data. The Central Bransfield Basin is dominated by two families of normal faults which are oriented northeast and northwest. The NE-trending faults define three graben systems that are roughly parallel to the basin axis. In an across-basin direction, the mean trend of this family of faults ranges from N71 (the graben system nearest to the Antarctic Peninsula) over N64 (the intermediate graben system), to N53 (the graben system nearest to the South Shetland Islands). The NW-trending family of faults is responsible for the deepening of the basin from southwest to northeast. Both families of faults define the overall Central Bransfield Basin structure, resulting in a complex division of the basin floor. Additionally, tens of volcanic edifices are located on the basin floor, the larger ones being associated to the NW-trending faults. Interaction of tectonics and sedimentation give place to the differentiation of three tectonostratigraphic units, TU1, TU2 and TU3 (from oldest to youngest). TU1 occupies the southernmost graben system, and it is affected by the NE-trending bounding normal faults. TU2 extends further northwestwards than TU1 and essentially fills the intermediate graben system. TU3 represents a further extension of the sediment infill over most of the Central Bransfield Basin, and marks the initiation of the infill of the northernmost graben system. Faults bounding this graben also determine the straight and abrupt morphology of the South Shetland Islands margin. The observed arrangement of the graben systems and the filling tectonostratigraphic units reveal a migration of extensional tectonics and associated depocentres from the Antarctic Peninsula margin to the South Shetland Island margin. The left-lateral rotation from N71 to N53 in the mean trend of the three successive graben systems could have been produced by the oblique subduction of the Phoenix plate and the effect of the sinistral strike-slip movement of the South Scotia Ridge, 200 km northeastwards of the Central Bransfield Basin.

DNA as molecular target of analogous palladium and platinum anti-Trypanosoma cruzi compounds: A comparative study

In the search for drugs with anti-trypanosome activity, we had previously synthesized two series of platinum and palladium analogous compounds of the formula [M(II)Cl(2)(HL)], where HL were bioactive 5-nitrofuryl or 5-nitroacroleine thiosemicarbazone derivatives. In this work, we thoroughly characterized [M(II)Cl(2)(HL)] complexes interaction with DNA by using different techniques: gel electrophoresis, DNA viscosity measurements, circular dichroism (CD) and atomic force microscopy (AFM). Electrophoresis results showed that all complexes induced a withdrawal of DNA superhelicity demonstrated by a decrease in electrophoretic mobility of supercoiled DNA form. This effect on migration was dependent on dose but also on the nature of both the metal and the ligand. In general, the effect produced by palladium complexes was significantly more intense than that observed for the corresponding platinum analogs. Differences between palladium and platinum complexes were also observed in CD experiments. While palladium complexes induce evident calf thymus (CT)-DNA profile changes compatible with B-DNA to Z-DNA conformational transition, no clear effect was observed for platinum ones. Additionally, AFM studies showed that changes in the shape of plasmid DNA, like supercoiling, kinks and thickness increase resulted more intense for the former. In addition, either Pd or Pt complexes increased the viscosity of CT DNA solutions in a concentration dependent manner. Although the nature of DNA interaction of both series of analogous palladium and platinum complexes seemed to be similar, an explanation for the observed differential intensity of the effect could be related to the known kinetic stability differences between palladium and platinum compounds.

Seismic stratigraphy of the Central Bransfield Basin (NW Antarctic Peninsula): interpretation of deposits and sedimentary processes in a glacio-marine environment

Abstract The Central Bransfield Basin is a deep narrow trough between the northern tip of the Antarctic Peninsula and the South Shetland Islands. Analyses of single-channel, high-resolution seismic reflection data are used to characterise the seismic stratigraphy of the Central Bransfield Basin. The tectonised acoustic basement is overlain by a 1-s-thick sedimentary cover composed of two main sedimentary sequences. The Lower Sequence, which shows synsedimentary deformation, has only been identified on the Antarctic Peninsula margin. The Upper Sequence is a complex sedimentary package composed of eight seismic units whose distribution, geometry and seismic facies allow two types of seismic units to be distinguished: slope and basinal units. The slope units, constituted by progradational stratified seismic facies, form a sedimentary wedge extending from the shelf edge. The basinal units fill the basin floor showing chaotic and undulated seismic facies that change basinward into stratified seismic facies. Both types of seismic units display an interfingering pattern at the base of the slope, suggesting an alternating shift of the sedimentary depocentre, from the slope to the basinfloor and vice versa. This alternate pattern indicates that the sedimentary processes responsible for the infilling of the Central Bransfield Basin followed a cyclic pattern, which has likely been associated with the advance and retreat of the ice sheets over the margins during glacial and interglacial episodes. During glacial periods, the ice sheets advanced, eroded the shallower sea floor areas and deposited diamicton and debris flow deposits along the moving grounding line, resulting in a progradational sedimentary wedge on the slope. At the end of glacial periods, coinciding with the retreat of the ice sheets, extensive sediment failures affected the continental margin. During interglacial periods the ice sheets remained restricted to coastal locations and glacial troughs, where processes of meltwater formation might have been significant. Sediment-laden underflows are generated within these troughs, from where they flow and spread over the shelf and down the slope to the basinfloor as sediment gravity flow deposits. The combined effect of these processes is a progradational build up of the shelf and an aggradational infilling of the basin floor, together with the development of the interfingering pattern at the base of the slope.

Induction of morphological changes in BEAS-2B human bronchial epithelial cells following chronic sub-cytotoxic and mildly cytotoxic hexavalent chromium exposures.

Certain hexavalent chromium (Cr(VI)) compounds are well established occupational respiratory tract carcinogens. However, despite extensive studies, the cellular and molecular mechanisms underlying Cr(VI)‐induced lung cancer remain poorly understood. In fact, the models used were often suboptimal and yielded conflicting results that were heavily dependent upon the system and experimental conditions employed. Here, we investigated the effects of chronic subcytotoxic and mildly cytotoxic (0.1–2 µM) Cr(VI) exposures on cultures of human bronchial epithelial cells, the main targets of Cr(VI) carcinogenicity. Our studies with the nontumorigenic BEAS‐2B cell line suggest that relatively short exposures (h) to sublethal Cr(VI) doses (0.1–1 µM) may render these cells less sensitive to contact inhibition. We have also observed a reduced sensitivity to Cr(VI)‐induced apoptosis shortly after the beginning of exposure to a mildly cytotoxic Cr(VI) dose (2 µM). Further studies are needed to determine whether these two phenotypes are involved in the Cr(VI)‐induced carcinogenic process. Additionally, evidence gathered in this study strongly points to a Cr(VI) interference with cell adhesion to the substratum and with cell–cell interactions. Finally, by chronically exposing BEAS‐2B cells to mildly cytotoxic Cr(VI) doses (1 and 2 µM), we were able to induce changes in cell morphology and pattern of growth characteristic of an early phase of pre‐malignant progression. Mol. Carcinog.

New π-arene ruthenium(II) piano-stool complexes with nitrogen ligands

The synthesis, characterization, DNA interaction and antiproliferative behavior of new π-arene ruthenium(II) piano-stool complexes with nitrogen ligands are described. Three series of organometallic compounds of formulae [RuCl(2)(η(6)-p-cym)L] were synthesized (with L=2-, 3- or 4-methylpyridine; L=2,3-, 2,4-, 2,5-, 3,4-, 3,5-dimethylpyridine and L=1,2-, 1,3- 1,4-methylaminobenzene). The crystal structures of [RuCl(2)(p-cym)(4-methylpyridine)], [RuCl(2)(p-cym)(3,4-dimethylpyridine)] and [RuCl(2)(p-cym)(1,4-methylaminobenzene)] were resolved and the characterization was completed by spectroscopic UV-vis, FT-IR and (1)H NMR studies. Electrochemical experiments were performed by cyclic voltammetry to estimate the redox potential of the Ru(II)/Ru(III) couple. The interaction with plasmid pBR322 DNA was studied through the examination of the electrophoretical mobility and atomic force microscopy, and interaction with ct-DNA by circular dichroism, viscosity measurements and fluorescence studies based on the DNA-ethidium bromide complex. The antiproliferative behavior of the series with L=methylpyridine was assayed against two tumor cell lines, i.e. LoVo and MiaPaca. The results revealed a moderate cytotoxicity with a higher activity for the LoVo cell line compared to the MiaPaca one.

Synthesis, Characterization and Biological Activity of trans-Platinum(II) and trans-Platinum(IV) Complexes with 4-Hydroxymethylpyridine

The synthesis and chemical characterization of two new trans platinum complexes, trans‐[PtCl2NH3(4‐hydroxymethylpyridine)] (1) and trans‐[PtCl4NH3(4‐hydroxymethylpyridine)] (2) are described. Their ability to interact with 5′‐GMP by themselves and in the presence of reducing agents in the case of trans‐[PtCl4NH3(4‐hydroxymethylpyridine)] were tested. Circular dichroism, electrophoretic mobility in agarose gel, and atomic force microscopy studies showed that the interaction of complex 1 with DNA is stronger than that of complex 2. Cytotoxicity tests against HL‐60 tumor cells also showed higher activity for trans‐[PtCl2NH3(4‐hydroxymethylpyridine)] than for trans‐[PtCl4NH3(4‐hydroxymethylpyridine)]. Complex 1 presents similar behavior to cisplatin, but with a lower IC50 at 24 h. Complex 1 also showed high apoptosis induction.

Oligomerization and DNA binding of Ler, a master regulator of pathogenicity of enterohemorrhagic and enteropathogenic Escherichia coli

Ler is a DNA-binding, oligomerizable protein that regulates pathogenicity islands in enterohemorrhagic and enteropathogenic Escherichia coli strains. Ler counteracts the transcriptional silencing effect of H-NS, another oligomerizable nucleoid-associated protein. We studied the oligomerization of Ler in the absence and presence of DNA by atomic force microscopy. Ler forms compact particles with a multimodal size distribution corresponding to multiples of 3–5 units of Ler. DNA wraps around Ler particles that contain more than 15–16 Ler monomers. The resulting shortening of the DNA contour length is in agreement with previous measurements of the length of DNA protected by Ler in footprinting assays. We propose that the repetition unit corresponds to the number of monomers per turn of a tight helical Ler oligomer. While the repressor (H-NS) and anti-repressor (Ler) have similar DNA-binding domains, their oligomerization domains are unrelated. We suggest that the different oligomerization behavior of the two proteins explains the opposite results of their interaction with the same or proximal regions of DNA.