Theoretical calculations on a series of dinuclear vanadium and niobium clusters

Electronic structures of chalcogenide-bridged binuclear clusters of vanadium and niobium with the {M₂(μ-Q₂)₂}⁴⁺, {M₂(μ-Q)₂}⁴⁺ and {M₂(μ-Q)(μ-Q)₂}⁴⁺ cores (Q = S, Se, Te) have been studied by density functional theory methods. In the vanadium clusters, the V-V distances are calculated to be in the range of 2.766-3.193 ?, whereas in the niobium clusters the calculated Nb-Nb bond lengths fall in the range of 2.881-3.380 ?, in accordance with the experimentally determined values. The calculated M-M bond distances generally decrease in the order {M₂(μ-Q₂)₂}⁴⁺ > {M₂(μ-Q)₂}⁴⁺ > {M₂(μ-Q)(μ-Q)₂}⁴⁺ (M = V, Nb, Q = S, Se). The calculated enthalpies of formation for the V clusters are higher than for the corresponding Nb clusters. On the other hand, the M₂Q₂ clusters have always higher enthalpies of formation than the M₂Q₃ species, and also (with the exception of M = V, Q = S) higher values of enthalpy of formation than for the M₂Q₄ species. The hardness η of the niobium clusters are higher than that of the vanadium analogs, except for the [V₂S₂(SH₂)₈]⁴⁺ case. The enthalpies ΔH₂₉₈ and the free energies ΔG₂₉₈ for the reactions of hydrogen addition to the [V₂(μ-S₂)₂(H₂O)₈]⁴⁺ and the [Nb₂(μ-S₂)₂(H₂O)₈]⁴⁺ clusters at constant pressure are −121.75 and −59.73 kJ/mol for the vanadium cluster, and 13.97 and 75.15 kJ/mol for the niobium cluster.     

Identification of Novel Type 2 Diabetes Candidate Genes Involved in the Crosstalk between the Mitochondrial and the Insulin Signaling Systems

Type 2 Diabetes (T2D) is a highly prevalent chronic metabolic disease with strong co-morbidity with obesity and cardiovascular diseases. There is growing evidence supporting the notion that a crosstalk between mitochondria and the insulin signaling cascade could be involved in the etiology of T2D and insulin resistance. In this study we investigated the molecular basis of this crosstalk by using systems biology approaches. We combined, filtered, and interrogated different types of functional interaction data, such as direct protein–protein interactions, co-expression analyses, and metabolic and signaling dependencies. As a result, we constructed the mitochondria-insulin (MITIN) network, which highlights 286 genes as candidate functional linkers between these two systems. The results of internal gene expression analysis of three independent experimental models of mitochondria and insulin signaling perturbations further support the connecting roles of these genes. In addition, we further assessed whether these genes are involved in the etiology of T2D using the genome-wide association study meta-analysis from the DIAGRAM consortium, involving 8,130 T2D cases and 38,987 controls. We found modest enrichment of genes associated with T2D amongst our linker genes (p = 0.0549), including three already validated T2D SNPs and 15 additional SNPs, which, when combined, were collectively associated to increased fasting glucose levels according to MAGIC genome wide meta-analysis (p = 8.12×10⁻⁵). This study highlights the potential of combining systems biology, experimental, and genome-wide association data mining for identifying novel genes and related variants that increase vulnerability to complex diseases.     

Cannabinoid receptors CB1 and CB2 form functional heteromers in brain

Exploring the role of cannabinoid CB(2) receptors in the brain, we present evidence of CB(2) receptor molecular and functional interaction with cannabinoid CB(1) receptors. Using biophysical and biochemical approaches, we discovered that CB(2) receptors can form heteromers with CB(1) receptors in transfected neuronal cells and in rat brain pineal gland, nucleus accumbens, and globus pallidus. Within CB(1)-CB(2) receptor heteromers expressed in a neuronal cell model, agonist co-activation of CB(1) and CB(2) receptors resulted in a negative cross-talk in Akt phosphorylation and neurite outgrowth. Moreover, one specific characteristic of CB(1)-CB(2) receptor heteromers consists of both the ability of CB(1) receptor antagonists to block the effect of CB(2) receptor agonists and, conversely, the ability of CB(2) receptor antagonists to block the effect of CB(1) receptor agonists, showing a bidirectional cross-antagonism phenomenon. Taken together, these data illuminate the mechanism by which CB(2) receptors can negatively modulate CB(1) receptor function.     

Maintenance of a high photosynthetic performance is linked to flooding tolerance in citrus

Citrus trees have been considered as flooding-sensitive although important differences in tolerance among species have been reported. The tolerance to flooding has been linked to optimal photosynthetic performance in other woody plants. To test whether there was a relationship between photosynthetic performance and flooding tolerance, leaf damage, chlorophyll content, net photosynthetic rate, stomatal conductance, the ratio of internal to ambient CO₂ concentration (C_i/C_a), water use efficiency and chlorophyll fluorescence parameters were studied in leaves of three citrus genotypes differing in their tolerance to flooding during continuous substrate flooding and alternate cycles of flooding and recovery. In Cleopatra and Citrumelo genotypes, marked reductions in net photosynthetic rate and stomatal conductance as well as increases in C_i/C_a in response to flooding stress were observed although with differences in the magnitude of the variation. In contrast, in Carrizo, a relatively flooding-tolerant genotype, there were no changes in net photosynthetic rate or in C_i/C_a and only a slight decrease in stomatal conductance occurred in response to flooding. Significant correlation between net photosynthetic rate and chlorophyll fluorescence parameters during flooding indicated a biochemical impairment of photosynthetic activity. This effect was apparently linked to damage in the PSII light-harvesting complexes induced by flooding and a subsequent effect on PSII to PSI electron flow that may alter the redox status in cells. Such biochemical impairment could lead to an increase in oxidative damage in Cleopatra and Citrumelo. The maintenance of good photosynthetic performance together with mechanisms to adjust electron flow in the photosynthetic apparatus could be linked to flooding tolerance in these woody plants.     

Use of Persistent Analogs of Abscisic Acid as Palliatives against Salt-stress Induced Damage in Citrus Plants

The effectiveness of several abscisic acid (ABA) analogs as palliatives against salt stress in intact citrus plants has been tested in this work. The effect of ABA, 8′-methylene ABA, 8′-acetylene ABA, ABA methyl ester, 8′-methylene ABA methyl ester, and 8′-acetylene ABA methyl ester on citrus responses to salt stress was studied on 2-year-old grafted plants. Leaf abscission, chloride accumulation, ethylene production, and net photosynthetic rate were the parameters used to characterize the performance of plants under stress. Data indicate that 8′-methylene ABA was the most effective compound in delaying the deleterious effects of high salinity on citrus plants. Its regular application reduced leaf chloride concentration, ethylene production, and leaf abscission. Furthermore, it delayed the depletion of CO₂ assimilation under these adverse conditions. Abscisic acid and 8′-acetylene ABA also reduced salt-stress induced injuries in citrus, although to a lower extent. Neither ABA methyl ester nor its 8′-C modified analogs showed biological activity in these assays.