Chloroplast ultrastructure and thylakoid polypeptide composition are affected by different salt concentrations in the halophytic plant Arthrocnemum macrostachyum

The effect of different external salt concentrations, from 0 mM to 1030 mM NaCl, on photosynthetic complexes and chloroplast ultrastructure in the halophyte Arthrocnemum macrostachyum was studied. Photosystem II, but not Photosystem I or cytochrome b6/f, was affected by salt treatment. We found that the PsbQ protein was never expressed, whereas the amounts of PsbP and PsbO were influenced by salt in a complex way. Analyses of Photosystem II intrinsic proteins showed an uneven degradation of subunits with a loss of about 50% of centres in the 0 mM NaCl treated sample. Also the shape of chloroplasts, as well as the organization of thylakoid membranes were affected by NaCl concentration, with many grana containing few thylakoids at 1030 mM NaCl and thicker grana and numerous swollen thylakoids at 0 mM NaCl. The PsbQ protein was found to be depleted also in thylakoids from other halophytes.     

Using mobility data in the design of optimal lockdown strategies for the COVID-19 pandemic

A mathematical model for the COVID-19 pandemic spread, which integrates age-structured Susceptible-Exposed-Infected-Recovered-Deceased dynamics with real mobile phone data accounting for the population mobility, is presented. The dynamical model adjustment is performed via Approximate Bayesian Computation. Optimal lockdown and exit strategies are determined based on nonlinear model predictive control, constrained to public-health and socio-economic factors. Through an extensive computational validation of the methodology, it is shown that it is possible to compute robust exit strategies with realistic reduced mobility values to inform public policy making, and we exemplify the applicability of the methodology using datasets from England and France.     

Activation pathways of alpha4beta1 integrin leading to distinct T-cell cytoskeleton reorganization, Rac1 regulation and Pyk2 phosphorylation

Alpha4beta1 integrin is highly expressed in lymphocytes and is essential in hematopoiesis, extravasation, and the inflammatory response. Alpha4beta1 can be activated by intracellular signals elicited upon T-cell activation by phorbol esters, CD3 crosslinking, or certain chemokine/receptor interactions (inside-out activation). Divalent cations or certain anti-beta1 mAbs (i.e., TS2/16) can also bind and activate integrins directly (outside-in activation). In both cases, activation results in increased adhesion and/or affinity for ligands. It is not known if these various stimuli produce the same or different post-adhesion events. To address this, we have studied the cytoskeleton organization and intracellular signaling following activation of 41 in Jurkat cells and in human T-lymphoblasts. Treatment with Mn2+, alpha-CD3 mAb or the chemokine SDF-1alpha followed by attachment to the fibronectin fragment H89 or the endothelial molecule VCAM-1 (alpha4beta1 ligands), resulted in cell polarization and migration. In contrast, activation with PMA or TS2/16 induced cell spreading and strong adherence. Video microscopy and Transwell analyses confirmed these results, which correlated with different resistance to detachment under flow. Activation of the small GTPase RhoA or transfection with the constitutively active mutants V14RhoA or V12Rac1, abolished the alpha4beta1-induced cell polarization but did not affect cell spreading. Moreover, Rac1 activity was distinctly modulated by agents that induce a polarized or spread phenotype. The tyrosine kinase Pyk2 was highly phosphorylated upon induction of cell polarity but not during cell spreading. These results reveal novel properties of alpha4beta1 integrin, namely the ability to trigger two types of T-cell cytoskeletal response with different signaling requirements.     

The function of peroxiredoxins in plant organelle redox metabolism

In 1996, cDNA sequences referred to as plant peroxiredoxins (Prx), i.e. a 1-Cys Prx and a 2-Cys Prx, were reported from barley. Ten years of research have advanced our understanding of plant Prx as thiol-based peroxide reductases with a broad substrate specificity, ranging from hydrogen peroxide to alkyl hydroperoxides and peroxinitrite. Prx have several features in common. (i) They are abundant proteins that are routinely detected in proteomics approaches. (ii) They interact with proteins such as glutaredoxins, thioredoxins, and cyclophilins as reductants, but also non-dithiol-disulphide exchange proteins. By work with transgenic plants, their activity was shown to (iii) affect metabolic integrity, (iv) protect DNA from damage in vitro and as shown here in vivo, and (v) modulate intracellular signalling related to reactive oxygen species and reactive nitrogen species. (vi) In all organisms Prx are encoded by small gene families that are of particular complexity in higher plants. A comparison of the Prx gene families in rice and Arabidopsis thaliana supports previous suggestions on Prx function in specific subcellular and metabolic context. (vii) Prx gene expression and activity are subjected to complex regulation realized by an integration of various signalling pathways. 2-Cys Prx expression depends on redox signals, abscisic acid, and protein kinase cascades. Besides these general properties, the chloroplast Prx have acquired specific roles in the context of photosynthesis. The thioredoxin-dependent peroxidase activity can be measured in crude plant extracts and contributes significantly to the overall H(2)O(2) detoxification capacity. Thus organellar Prx proteins enable an alternative water-water cycle for detoxification of photochemically produced H(2)O(2), which acts independently from the ascorbate-dependent Asada-Halliwell-Foyer cycle. 2-Cys Prx and Prx Q associate with thylakoid membrane components. The mitochondrial PrxII F is essential for root growth under stress. Following a more general introduction, the paper summarizes present knowledge on plant organellar Prx, addressing Prx in signalling, and also suggests some lines for future research.     

Structure, surface interactions, and compressibility of bacterial S-layers through scanning force microscopy and the surface force apparatus

Two-dimensional crystalline bacterial surface layers (S-layers) are found in a broad range of bacteria and archaea as the outermost cell envelope component. The self-assembling properties of the S-layers permit them to recrystallize on solid substrates. Beyond their biological interest as S-layers, they are currently used in nanotechnology to build supramolecular structures. Here, the structure of S-layers and the interactions between them are studied through surface force techniques. Scanning force microscopy has been used to study the structure of recrystallized S-layers from Bacillus sphaericus on mica at different 1:1 electrolyte concentrations. They give evidence of the two-dimensional organization of the proteins and reveal small corrugations of the S-layers formed on mica. The lattice parameters of the S-layers were a=b=14 nm, gamma=90 degrees and did not depend on the electrolyte concentration. The interaction forces between recrystallized S-layers on mica were studied with the surface force apparatus as a function of electrolyte concentration. Force measurements show that electrostatic and steric interactions are dominant at long distances. When the S-layers are compressed they exhibit elastic behavior. No adhesion between recrystallized layers takes place. We report for the first time, to our knowledge, the value of the compressibility modulus of the S-layer (0.6 MPa). The compressibility modulus is independent on the electrolyte concentration, although loads of 20 mN m-1 damage the layer locally. Control experiments with denatured S-proteins show similar elastic properties under compression but they exhibit adhesion forces between proteins, which were not observed in recrystallized S-layers.     

Competitive binding of cholesterol and ergosterol to the polyene antibiotic nystatin. A fluorescence study

Competition studies between cholesterol and ergosterol were carried out to gain insight into the binding interactions between nystatin and these sterols. Lipid vesicles were prepared with mixtures of palmitoyloleoylphosphocholine/ergosterol/cholesterol, and both sterol molar ratio and total content were varied. The inhibitory effect of cholesterol toward the ergosterol ability to induce the formation of long-lived fluorescent antibiotic species was used to detect nystatin-cholesterol interactions. It was found that the key factor controlling nystatin photophysical properties in the ternary lipid mixtures was their ergosterol/cholesterol molar ratio and not their overall sterol content. Moreover, permeabilization studies showed that nystatin was able to form pores in all the mixed vesicles, but the initial rate of pore formation was also dependent on the ergosterol/cholesterol molar ratio. Our data show that ergosterol is displaced by competing cholesterol, indirectly confirming cholesterol's ability to coassemble with nystatin. The distinct spectroscopic properties emphasize the different molecular architecture adopted by nystatin-cholesterol and -ergosterol complexes, and therefore are relevant to understanding the interaction of the antibiotic with membranes.     

Vanadyl(IV) complexes with saccharides. Bioactivity in osteoblast-like cells in culture

Complexes of vanadyl(IV) with 4 monosaccharides and 5 disaccharides were tested in 2 osteoblast-like cell lines (MC3T3E1 and UMR106). Many complexes caused stimulation of UMR106 proliferation (120% basal) in the range of 2.5 to 25 micromol/L. In the nontransformed osteoblasts, some vanadyl-saccharide complexes stimulated the mitogenesis (115% basal) in the same range of concentration. The glucose and sucrose complexes were the most efficient inhibitory agents (65% and 88% of inhibition vs. basal, respectively) for tumoral cells at 100 micromol/L. The galactose and turanose complexes exerted a similar effect in the nontransformed osteoblasts. On the other hand, all the complexes promoted the phosphorylation of the extracellular regulated kinases (ERKs). All together, these results indicate that the stimulation of ERKs is not the only factor that plays a role in the proliferative effects of vanadium derivatives since some compounds were inhibitory proliferating agents. Cell differentiation was evaluated by alkaline phosphatase specific activity and collagen synthesis in UMR106 cells. All the complexes inhibited alkaline phosphatase activity, with galactose complex as the most effective compound (IC50 = 43 micromol/L). The complex with the trehalose TreVO was the most effective agent to stimulate collagen synthesis (142% basal) and glucose consumption (132% basal). A cytosolic tyrosine protein kinase and the kinase-3 of glycogen synthase seem to be involved in the stimulation of glucose consumption by vanadium derivatives. In this series, only TreVO gathered the characteristics of a good insulin mimetic and osteogenic drug. In addition, this complex was a good promoting agent of nontransformed osteoblast proliferation, whereas it inhibited tumoral osteoblasts. GluVO, the complex with glucose, was also more toxic for tumoral than for nontransformed cells. These 2 vanadium derivatives are good potential antitumoral drugs. All the results suggest that the biological effects of vanadium compounds are a complex phenomenon influenced by the complexation, the dose, and the nature of the ligands and the cells.     

Tetraspanins CD9 and CD81 modulate HIV-1-induced membrane fusion

Protein organization on the membrane of target cells may modulate HIV-1 transmission. Since the tetraspanin CD81 is associated to CD4, the receptor of HIV-1 envelope protein (Env; gp120/gp41), we have explored the possibility that this molecule may modulate the initial steps of HIV-1 infection. On the other hand, CD81 belongs to the tetraspanin family, which has been described as organizers of protein microdomains on the plasma membrane. Therefore, the role of CD81 and other related tetraspanin, CD9, on the cell-to-cell fusion process mediated by HIV-1 was studied. We found that anti-tetraspanin Abs enhanced the syncytia formation induced by HIV-1 envelope proteins and viral entry in human T lymphoblasts. In addition, anti-CD81 Abs triggered its clustering in patches, where CD4 and CXCR4 were included. Moreover, the knocking down of CD81 and CD9 expression resulted in an increase in syncytia formation and viral entry. Accordingly, overexpression of CD81 and CD9 rendered cells less susceptible to Env-mediated syncytia formation. These data indicate that CD9 and CD81 have an important role in membrane fusion induced by HIV-1 envelope.     

Correlation between oxidative Stress and Alteration of Intracellular Calcium Handling in Isoproterenol-Induced Myocardial Infarction

Myocardial Ca²⁺ overload and oxidative stress are well documented effects associated to isoproterenol (ISO)-induced myocardial necrosis, but information correlating these two issues is scarce. Using an ISO-induced myocardial infarction model, 3 stages of myocardial damage were defined: pre-infarction (0–12 h), infarction (12–24 h) and post-infarction (24–96 h). Alterations in Ca²⁺ homeostasis and oxidative stress were studied in mitochondria, sarcoplasmic reticulum and plasmalemma by measuring the Ca²⁺ content, the activity of Ca²⁺ handling proteins, and by quantifying TBARs, nitric oxide (NO) and oxidative protein damage (changes in carbonyl and thiol groups). Free radicals generated system, antioxidant enzymes and oxidative stress (GSH/GSSG ratio) were also monitored at different times of ISO-induced cardiotoxicity. The Ca²⁺ overload induced by ISO was counterbalanced by a diminution in the ryanodine receptor activity and the Na⁺-Ca⁺² exchanger as well as by the increase in both calcium ATPases activities (vanadate- and thapsigargine-sensitive) and mitochondrial Ca²⁺ uptake during pre-infarction and infarction stages. Pro-oxidative reactions and antioxidant defences during the 3 stages of cardiotoxicity were observed, with maximal oxidative stress during the infarction. Significant correlations were found among pro-oxidative reactions with plasmalemma and sarcoplasmic reticulum Ca²⁺ ATPases, and ryanodine receptor activities at the onset and development of ISO-induced infarction. These findings could be helpful in the design of antioxidant therapies in this pathology.