Xanthophyll-induced aggregation of LHCII as a switch between light-harvesting and energy dissipation systems

The xanthophyll cycle pigments, violaxanthin and zeaxanthin, present outside the light-harvesting pigment-protein complexes of Photosystem II (LHCII) considerably enhance specific aggregation of proteins as revealed by analysis of the 77 K chlorophyll a fluorescence emission spectra. Analysis of the infrared absorption spectra in the Amide I region shows that the aggregation is associated with formation of intermolecular hydrogen bonding between the alpha helices of neighboring complexes. The aggregation gives rise to new electronic energy levels, in the Soret region (530 nm) and corresponding to the Q spectral region (691 nm), as revealed by analysis of the resonance light scattering spectra. New electronic energy levels are interpreted in terms of exciton coupling of protein-bound photosynthetic pigments. The energy of the Q excitonic level of chlorophyll is not high enough to drive the light reactions of Photosystem II but better suited to transfer excitation energy to Photosystem I, which creates favourable energetic conditions for the state I-state II transition. The lack of fluorescence emission from this energy level, at physiological temperatures, is indicative of either very high thermal energy conversion rate or efficient excitation quenching by carotenoids. Chlorophyll a fluorescence was quenched up to 61% and 34% in the zeaxanthin- and violaxanthin-containing samples, respectively, as compared to pure LHCII. Enhanced aggregation of LHCII, observed in the presence of the xanthophyll cycle pigments, is discussed in terms of the switch between light-harvesting and energy dissipation systems.     

Interferon-induced thyroiditis during treatment of chronic hepatitis C

Thyroid function disorders affect between 5% and 15% of patients treated with IFNα and RBV for chronic hepatitis C. Women and patients with thyroid peroxidase antibodies (TPOAb) found before the treatment are at risk of developing the disorders (46.1% vs. 5.4%). The spectrum of IFNα-induced thyroiditis (IIT) includes two groups. Disorders with an autoimmune background are: presence of thyroid autoantibodies without clinical disease, Hashimoto's disease and Graves' disease. The second group comprises diseases caused by the direct toxic effect of IFNα on the thyroid gland, i.e. destructive thyroiditis and non-autoimmune hypothyroidism. Thyroid diseases are not an absolute contraindication for IFNα and RBV therapy. In patients diagnosed with thyroid dysfunction, before the antiviral therapy it is necessary to achieve euthyreosis. Thyroid function disorders may occur at any moment of the therapy. The earliest have been observed in the 4th week of treatment, and the latest 12 months after its termination. During the therapy, in order to diagnose IIT early, it is recommended to determine TSH level every 2-3 months depending on the presence of TPOAb before the treatment. The diagnosis and treatment of thyroid function disorders should be conducted in co-operation with an endocrinologist.     

Strong light-induced reorganization of pigment-protein complexes of thylakoid membranes in rye (spectroscopic study)

The supramolecular reorganization of LHCII complexes within the thylakoid membrane in Secale cereale leaves under low and high light condition was examined. Rye seedlings were germinated hydroponically in a climate chamber with a 16 h daylight photoperiod, photosynthetic photon flux density (PPFD) of 150 μmol m⁻² s⁻¹ and 24/16 °C day/night temperature. The influence of pre-illumination of the plants with high light intensity on the PSII antenna complexes was studied by comparison of the structure and function of the LHCII complexes and organization of thylakoid membranes isolated from 10-day-old plants illuminated with low (150 μmol m⁻² s⁻¹) or high (1200 μmol m⁻² s⁻¹) light intensity. Aggregated and trimeric with monomeric forms of LHCII complexes were separated from the whole thylakoid membranes using non-denaturing electrophoresis. Analyses of fluorescence emission spectra of these different LHCII forms showed that the monomer was the most effective aggregating antenna form. Moreover, photoprotection connected with LHCII aggregation was more effective upon LHCII monomers in comparison to trimer aggregation. Light stress induced specific organization of neighboring LHCII complexes, causing an increase in fluorescence yield of the long-wavelength bands (centered at 701 and 734 nm). The changes in the organization of the thylakoid membrane under light stress, observed by analysis of absorbance spectra obtained by Fourier transform infrared spectroscopy, also indicated light-induced LHCII aggregation.     

Cooperativity of peptidoglycan synthases active in bacterial cell elongation

Clostridium perfringens possesses at least two functional quorum sensing (QS) systems, i.e. an Agr-like system and a LuxS-dependent AI-2 system. Both of those QS systems can reportedly control in vitro toxin production by C. perfringens but their importance for virulence has not been evaluated. Therefore, the current study assessed whether these QS systems might regulate the pathogenicity of CN3685, a C. perfringens type C strain. Since type C isolates cause both haemorrhagic necrotic enteritis and fatal enterotoxemias (where toxins produced in the intestines are absorbed into the circulation to target other internal organs), the ability of isogenic agrB or luxS mutants to cause necrotizing enteritis in rabbit small intestinal loops or enterotoxemic lethality in mice was evaluated. Results obtained strongly suggest that the Agr-like QS system, but not the LuxS-dependent AI-2 QS system, is required for CN3685 to cause haemorrhagic necrotizing enteritis, apparently because the Agr-like system regulates the production of beta toxin, which is essential for causing this pathology. The Agr-like system, but not the LuxS-mediated AI-2 system, was also important for CN3685 to cause fatal enterotoxemia. These results provide the first direct evidence supporting a role for any QS system in clostridial infections.     

Main dietary compounds and pancreatic cancer risk. The quantitative analysis of case-control and cohort studies

Objective: Estimation of the role of main dietary compounds in the risk of developing pancreatic cancer. Research methods and procedures: Literature published till 2010 was reviewed and selected for further analysis. The used terms were: red meat, minced meat, ham, bacon, sausages, white meat, poultry, vegetables, fish, eggs, fruits, lifestyle, diet, pancreatic cancer and pancreatic neoplasm. The collected data were meta-analysed with calculation of combined relative risk and 95% confidence interval as well as studies heterogeneity. Results: A meta-analysis of 11 case–control studies indicates that red meat ingestion elevates pancreatic cancer risk by 48% (95% CI = 1.25–1.76). The vegetables and fruit reduce the risk by 38% (95% CI = 0.54–0.73) and 29% (95% CI = 0.59–0.84), respectively. The pooled analyses of 10 cohort studies do not show significant relations between main dietary compound ingestion and pancreatic cancer risk. Conclusion: The red meat intake is associated with elevated risk of pancreatic cancer in contrast to vegetables and fruit ingestion. The ingestion of red meat, vegetables and fruit in cohort studies was not influenced on pancreatic cancer risk. The role of fish, poultry and eggs was not significant in both case–control and cohort studies, thus further studies were needed.     

Ephs and ephrins in cancer: ephrin-A1 signalling

Ephrin-A1 and its primary receptor, EphA2, are involved in numerous physiological processes and have been intensely studied for their roles in malignancy. Ephrin-Eph signalling is complex on its own and is also cell-type dependent, making elucidation of the exact role of ephrin-A1 in neoplasia challenging. Multiple oncogenic signalling pathways, such as MAP/ERK and PI3K are affected by ephrin-A1, and in some cases evidence suggests the promotion of a specific pathway in one cell or cancer type and inhibition of the same pathway in another type of cell or cancer. Ephrin-A1 also plays an integral role in angiogenesis and tumor neovascularization. Until recently, studies investigating ephrins focused on the ligands as GPI-anchored proteins that required membrane anchoring or artificial clustering for Eph receptor activation. However, recent studies have demonstrated a functional role for soluble, monomeric ephrin-A1. This review will focus on various forms of ephrin-A1-specific signalling in human malignancy.     

Significant contribution of the pgdA gene to the virulence of Streptococcus suis

Streptococcus suis is a major swine pathogen and emerging zoonotic agent. In this study we have determined the muropeptide composition of S. suis peptidoglycan (PG) and found, among other modifications, N-deacetylated compounds. Comparison with an isogenic mutant showed that the product of the pgdA gene is responsible for this specific modification which occurred in very low amounts. Low level of PG N-deacetylation correlated with absence of significant lysozyme resistance when wild-type S. suis was grown in vitro. On the other hand, expression of the pgdA gene was increased upon interaction of the bacterium with neutrophils in vitro as well as in vivo in experimentally inoculated mice, suggesting that S. suis may enhance PG N-deacetylation under these conditions. Evaluation of the DeltapgdA mutant in both the CD1 murine and the porcine models of infection revealed a significant contribution of the pgdA gene to the virulence traits of S. suis. Reflecting a severe impairment in its ability to persist in blood and decreased ability to escape immune clearance mechanisms mediated by neutrophils, the DeltapgdA mutant was highly attenuated in both models. The results of this study suggest that modification of PG by N-deacetylation is an important factor in S. suis virulence.     

Effect of a short-term hypoxic treatment followed by re-aeration on free radicals level and antioxidative enzymes in lupine roots.

To investigate whether re-aeration after a short-term hypoxic pre-treatment (for 2, 12 or 24 h) induces oxidative stress, the temporal sequence of physiological reactions, including the level of free radicals, hydrogen peroxide production, and changes in antioxidative enzymes, was characterized in roots of hydroponically grown lupine (Lupinus luteus L., cv. Juno) seedlings. By using electron paramagnetic resonance (EPR), we found that the exposure of hypoxically grown roots (hypoxic pre-treatment for 12 and 24 h) to air caused an increase in the level of free radicals. The amount of hydrogen peroxide also tended to increase when hypoxically pre-treated roots were re-aerated, which attests to a higher production of reactive oxygen species. Re-aeration caused a higher activity of superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6), whereas the activity of peroxidase (POX, EC 1.11.1.7) was only slightly influenced. The roots were less tolerant to longer hypoxic pre-treatments, with a significant decrease in viability, associated with death of root tips immediately after hypoxic stress. Roots exposed to hypoxia for 2 h showed less pronounced responses and their viability was not affected by hypoxic stress and re-aeration. These results indicate that re-aeration following short-term hypoxia imposes a mild oxidative stress. This led us to conclude that re-oxygenation stress per se was not the key factor for cell death in root tips.