The single tryptophan of the PsbQ protein of photosystem II is at the end of a 4-alpha-helical bundle domain.

We examined the microenvironment of the single tryptophan and the tyrosine residues of PsbQ, one of the three main extrinsic proteins of green algal and higher plant photosystem II. On the basis of this information and the previous data on secondary structure [Balsera, M., Arellano, J.B., Gutiérrez, J.R., Heredia, P., Revuelta, J.L. & De Las Rivas, J. (2003) Biochemistry42, 1000-1007], we screened structural models derived by combining various threading approaches. Experimental results showed that the tryptophan residue is partially buried in the core of the protein but still in a polar environment, according to the intrinsic fluorescence emission of PsbQ and the fact that fluorescence quenching by iodide was weaker than that by acrylamide. Furthermore, quenching by cesium suggested that a positively charged barrier shields the tryptophan microenvironment. Comparison of the absorption spectra in native and denaturing conditions indicated that one or two out of six tyrosines of PsbQ are buried in the core of the structure. Using threading methods, a 3D structural model was built for the C-terminal domain of the PsbQ protein family (residues 46-149), while the N-terminal domain is predicted to have a flexible structure. The model for the C-terminal domain is based on the 3D structure of cytochrome b562, a mainly alpha-protein with a helical up/down bundle folding. Despite the large sequence differences between the template and PsbQ, the structural and energetic parameters for the explicit model are acceptable, as judged by the corresponding tools. This 3D model is compatible with the experimentally determined environment of the tryptophan residue and with published structural information. The future experimental determination of the 3D structure of the protein will offer a good validation point for our model and the technology used. Until then, the model can provide a starting point for further studies on the function of PsbQ.     

Surface Plasmon Enhancement at a Liquid–Metal–Liquid Interface

Herein, we report the first experimental demonstration of surface plasmon enhancement at a liquid–metal–liquid interface using a pseudo-Kretschmann geometry. Pumping gold nanoparticle clusters at the interface of a p-xylene–water mixture, we were able to measure a fluorescence enhancement of three orders of magnitude in Rose Bengal at an excitation wavelength of 532 nm. The observed increase is due to the local electric field enhancement and the reduction of the fluorescence lifetime of dye molecules in the close vicinity of the metal surface. Theoretical modeling using the T-matrix method of the electric field intensity enhancement of emulated surfaces supports the experimental results. This new approach will open a new road for the study of dynamic systems using plasmonics.     

A core of three amino acids at the carboxyl‐terminal region of glutamine synthetase defines its regulation in cyanobacteria

Glutamine synthetase (GS) type I is a key enzyme in nitrogen metabolism, and its activity is finely controlled by cellular carbon/nitrogen balance. In cyanobacteria, a reversible process that involves protein–protein interaction with two proteins, the inactivating factors IF7 and IF17, regulates GS. Previously, we showed that three arginine residues of IFs are critical for binding and inhibition of GS. In this work, taking advantage of the specificity of GS/IFs interaction in the model cyanobacteria Synechocystis sp. PCC 6803 and Anabaena sp. PCC 7120, we have constructed a different chimeric GSs from these two cyanobacteria. Analysis of these proteins, together with a site‐directed mutagenesis approach, indicates that a core of three residues (E419, N456 and R459) is essential for the inactivation process. The three residues belong to the last 56 amino acids of the C‐terminus of Synechocystis GS. A protein–protein docking modeling of Synechocystis GS in complex with IF7 supports the role of the identified core for GS/IF interaction.     

The Colonisation of Exotic Species Does Not Have to Trigger Faunal Homogenisation: Lessons from the Assembly Patterns of Arthropods on Oceanic Islands

Human-caused disturbances can lead to the extinction of indigenous (endemic and native) species, while facilitating and increasing the colonisation of exotic species; this increase can, in turn, promote the similarity of species compositions between sites if human-disturbed sites are consistently invaded by a regionally species-poor pool of exotic species. In this study, we analysed the extent to which epigean arthropod assemblages of four islands of the Azorean archipelago are characterised by nestedness according to a habitat-altered gradient. The degree of nestedness represents the extent to which less ubiquitous species occur in subsets of sites occupied by the more widespread species, resulting in an ordered loss/gain of species across environmental or ecological gradients. A predictable loss of species across communities while maintaining others may lead to more similar communities (i.e. lower beta-diversity). In contrast, anti-nestedness occurs when different species tend to occupy distinct sites, thus characterising a replacement of species across such gradients. Our results showed that an increase in exotic species does not promote assemblage homogenisation at the habitat level. On the contrary, exotic species were revealed as habitat specialists that constitute new and well-differentiated assemblages, even increasing the species compositional heterogeneity within human-altered landscapes. Therefore, contrary to expectations, our results show that both indigenous and exotic species established idiosyncratic assemblages within habitats and islands. We suggest that both the historical extinction of indigenous species in disturbed habitats and the habitat-specialised character of some exotic invasions have contributed to the construction of current assemblages.     

Lipid hydroperoxide-induced and hemoglobin-enhanced oxidative damage to colon cancer cells

Epidemiological studies have indicated that Western diets are related to an increase in a series of malignancies. Among the compounds that are credited for this toxic effect are heme and lipid peroxides. We evaluated the effects of hemoglobin (Hb) and linoleic acid hydroperoxides (LAOOH) on a series of toxicological endpoints, such as cytotoxicity, redox status, lipid peroxidation, and DNA damage. We demonstrated that the preincubation of SW480 cells with Hb and its subsequent exposure to LAOOH (Hb + LAOOH) led to an increase in cell death, DCFH oxidation, malonaldehyde formation, and DNA fragmentation and that these effects were related to the peroxide group and the heme present in Hb. Furthermore, Hb and LAOOH alone exerted a toxic effect on the endpoints assayed only at concentrations higher than 100 μM. We were also able to show that SW480 cells presented a higher level of the modified DNA bases 8-oxo-7,8-dihydro-2′-deoxyguanosine and 1,N²-etheno-2′-deoxyguanosine compared to the control. Furthermore, incubations with Hb led to an increase in intracellular iron levels, and this high level of iron correlated with DNA oxidation, as measured as EndoIII- and Fpg-sensitive sites. Thus, Hb from either red meat or bowel bleeding could act as an enhancer of fatty acid hydroperoxide genotoxicity, which contributes to the accumulation of DNA lesions in colon cancer cells.     

Mutational analysis of the inactivating factors, IF7 and IF17 from Synechocystis sp. PCC 6803: critical role of arginine amino acid residues for glutamine synthetase inactivation

The Synechocystis sp. PCC 6803 glutamine synthetase type I (GS) activity is controlled by a process that involves protein-protein interaction with two inactivating factors (IF7 and IF17). IF7 is a natively unfolded, 65-residue-long protein, homologous to the carboxy-terminal region of IF17. Both proteins have abundance of positively charged amino acid residues and a high isoelectric point. In this study, we analyse the IF amino acid residues involved in GS inactivation by a mutational approach, both in vitro and in vivo. The results clearly indicate that the GS-IF complex formation must be determined mainly by electrostatic interactions. We have identified three conserved arginine residues of IF7 and IF17 that are essential for the interaction of these proteins with GS. All these residues map in the homologous region of IFs. Furthermore, in vitro analysis of a truncated IF17 protein without the 82-residue-long amino-terminal part, together with the analysis of a Synechocystis strain expressing a chimeric protein, containing this amino-terminal part of IF17 fused to IF7, demonstrates that amino-terminal region of IF17 mostly confers a higher stability to this protein.     

Brahma is required for proper expression of the floral repressor FLC in Arabidopsis

Background

BRAHMA (BRM) is a member of a family of ATPases of the SWI/SNF chromatin remodeling complexes from Arabidopsis. BRM has been previously shown to be crucial for vegetative and reproductive development.

Methodology/Principal Findings

Here we carry out a detailed analysis of the flowering phenotype of brm mutant plants which reveals that, in addition to repressing the flowering promoting genes CONSTANS (CO), FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1), BRM also represses expression of the general flowering repressor FLOWERING LOCUS C (FLC). Thus, in brm mutant plants FLC expression is elevated, and FLC chromatin exhibits increased levels of histone H3 lysine 4 tri-methylation and decreased levels of H3 lysine 27 tri-methylation, indicating that BRM imposes a repressive chromatin configuration at the FLC locus. However, brm mutants display a normal vernalization response, indicating that BRM is not involved in vernalization-mediated FLC repression. Analysis of double mutants suggests that BRM is partially redundant with the autonomous pathway. Analysis of genetic interactions between BRM and the histone H2A.Z deposition machinery demonstrates that brm mutations overcome a requirement of H2A.Z for FLC activation suggesting that in the absence of BRM, a constitutively open chromatin conformation renders H2A.Z dispensable.

Conclusions/Significance

BRM is critical for phase transition in Arabidopsis. Thus, BRM represses expression of the flowering promoting genes CO, FT and SOC1 and of the flowering repressor FLC. Our results indicate that BRM controls expression of FLC by creating a repressive chromatin configuration of the locus.     

Synergism between prior Anisakis simplex infections and intake of NSAIDs, on the risk of upper digestive bleeding: a case-control study

Background

The aim of this study was to investigate the relationship between prior Anisakis infections and upper gastrointestinal bleeding (UGIB), and its interaction with non-steroidal anti-inflammatory drug (NSAID) intake.

Methods/Principal Findings

We conducted a hospital-based case-control study covering 215 UGIB cases and 650 controls. Odds ratios (ORs) with their confidence intervals (95% CIs) were calculated, as well as the ratio of the combined effects to the sum of the separate effects of Anisakis allergic sensitization and NSAIDs intake. Prior Anisakis infections were revealed by the presence of anti-Anisakis IgE antibodies specific to the recombinant Ani s 1 and Ani s 7 allergens used as the targets in indirect ELISA. Prior Anisakis infections (OR 1.74 [95% CI: 1.10 to 2.75]) and the intake of NSAIDs (OR 6.63 [95% CI: 4.21 to 10.43]) increased the risk of bleeding. Simultaneous NSAIDs intake and Anisakis allergic sensitization increased the risk of UGIB 14-fold (OR = 14.46 [95% CI: 6.08 to 34.40]). This interaction was additive, with a synergistic index of 3.01 (95% CI: 1.18–7.71).

Conclusions

Prior Anisakis infection is an independent risk factor for UGIB, and the joint effect with NSAIDs is 3 times higher than the sum of their individual effects.     

Antagonistic Effect of Luzindole in Mice Treated with Melatonin During the Infection with the Venezuelan Equine Encephalomyelitis Virus

The effect of Luzindole (LZ) in mice treated with melatonin (MEL) during the infection with the Venezuelan equine encephalomyelitis (VEE) virus was examined. Melatonin (500 μg/Kg b.w.) was administered daily 3 days before and 5 days after the infection. Luzindole (5 mg/Kg b.w.) was injected intraperitoneally 3 days before (pre-infection) or 5 days after (post-infection) the infection. Mortality rates in the infected mice treated both with MEL and LZ were higher than in those treated with MEL alone in which the lowest brain and serum viral titers were detected. On the third post-infection day, viral titers of the MEL + VEE + LZ (pre-infection) group were higher than those of the remainder groups. On the fifth day, viral titers in infected mice were similar to those of the MEL + VEE + LZ (pre-infection) group, but higher than those detected in the MEL + VEE + LZ (post-infection). In conclusion, the protective effect of MEL in mice infected with VEE virus was inhibited by LZ suggesting that this protection is mediated by MEL receptors.     

Conditions for open-air outdoor culture of Dunaliella salina in southern Spain

The optimization of the operation, under the climatic conditions of southern Spain, of an experimental plant for -carotene production by Dunaliella has been pursued. The effects of mixing, culture depth, cell density and dilution cycles on -carotene and biomass productivity were studied under a semicontinuous culture regime in open tanks outdoors. Using 3 m²-surface containers, the highest productivity values, for both -carotene and biomass, were recorded with a flow rate of 0.55 m s^–1; 10 cm depth; 0.7 – 0.9 × 10⁶cell ml^–1, population density; and dilution cycles of two days. An average annual productivity of 1.65 g (dry wt) m^–2 d^–1 was estimated for Dunaliella biomass, being that for -carotene of about 0.1 g m^–2 d^–1. Under these optimized conditions, experiments have been carried out at the Cadiz Bay with 20 m²-surface tanks during a whole-year cycle. The results obtained have validated this location and the operating conditions established as being most appropriate for efficient mass production of -carotene rich D. salina.