Further investigation on the lateral and transversal proton currents at the thylakoid membrane level by hydrogen-deuterium exchange

Energetically-coupled processes (electron flow, proton uptake and correlated pH gradient) were investigated on envelope-free chloroplasts of lettuce suspended in ¹H₂O or ²H₂O media. Study of the light-intensity and temperature dependencies of these phenomena led to the following observations: 1. At neutral pH, ²H₂O diminishes the transmembrane H⁺ gradient in strong light (chain Photosystem II + Photosystem I) but not in low light; the total H⁺ uptake is increased at all light intensities: the buffering capacity of the inner compartment is increased in heavy water, possibly through enhancement of interactions between membranous titrable groups and the aqueous phase. 2. ²H₂O does not affect the photochemical events of the redox chain, whatever the electron pathway (PSII, PSI or PSII + PSI): only thermal steps are inhibited. The diminution of the apparent quantum yield, sometimes observed, may be ascribed to the dual site of action of the artificial redox carrier (ferricyanide) then used. 3. ²H₂O does not modify the activation energy of the limiting step of the electron flow (PSII + PSI) in uncoupled (44 vs. 47 kJ · mol^?1) or — but less clearly — in coupled, i.e., ‘basal’, state (55 vs. 59 kJ · mol^?1). ²H₂O does not either change the temperature of the phase transition of the membrane (17°C) for the uncoupled flow. However, a low-temperature transition, observed only for the coupled chain, is slightly increased by ²H₂O; this thermal transition is attributed to the freezing of some bound water near the plastoquinone pool. 4. Δp²H is smaller than Δp¹H at all temperatures (PSII + PSI chain). ΔpH is quasi-constant from 0°C to 10°C, then decreases when temperature rises. ²H₂O does not change the activation energy of the dark passive H⁺ efflux, which is almost twice that of the coupled electron flow. The phase transition at low temperature suggests that the proton efflux occurs via two parallel pathways, one temperature-dependent and the other temperature-independent. Except for the increase of the internal buffering capacity, the effects of ²H₂O on the membrane conformation seem limited, as shown by the unchanged activation energies of the electron flow and of the H⁺ leakage. The null activation energy observed at low temperature emphasizes the role of the bound water in these processes; however, the different effects of ²H₂O on the transition temperatures indicate that this bound water has different properties when associated with the translocation sites or with the H⁺ leakage ones. This ‘microcompartmentation’ of the membranes is consistent with the concept of lateral pH heterogeneity we have previously suggested (de Kouchkovsky, Y., and Haraux, F. (1981) Biochem. Biophys. Res. Commun. 99, 205–212). The theoretical computations and the experimental results suggest that in the steady state, the internal pH would be several tenths of a ‘unit’ lower near the plastoquinones than near the H⁺ efflux sites (coupling factors); this difference would be increased when ²H₊ replaces ¹H⁺, owing to the lower mobility of the deuteron. It is concluded that local, and not average, pH (and ΔpH) should be considered for the understanding of the energy transduction processes.     

Structure-based discovery of novel flavonol inhibitors of human protein kinase CK2

Serine/threonine protein kinase CK2 controls vast variety of fundamental processes in cell life; however, despite long period of study, its functional role is not completely determined. CK2 has a significant pathogenic potential and its activity is strictly associated with the development of various kinds of disorders. There are a growing number of facts that inhibitors of CK2 could be used as pharmaceutical agents for the cancer treatment, viral infections, and inflammatory diseases. In this article, we report structural and biological data on the novel synthetic flavonol derivatives, 3-hydroxy-4'-carboxyflavones, possessing a high inhibitory activity toward CK2. With the aid of combinatorial organic synthesis, molecular modeling techniques and biochemical in vitro tests, we studied the structure-activity relationships of flavonol derivatives and developed binding model describing their key intermolecular interactions with the CK2 ATP-binding site. Obtained data show that the synthetic 3-hydroxy-4'-carboxyflavones possess the highest activity among flavonol inhibitors of CK2 known till date.     

Sea Anemone Peptide with Uncommon β-Hairpin Structure Inhibits Acid-sensing Ion Channel 3 (ASIC3) and Reveals Analgesic Activity

Three novel peptides were isolated from the venom of the sea anemone Urticina grebelnyi. All of them are 29 amino acid peptides cross-linked by two disulfide bridges, with a primary structure similar to other sea anemone peptides belonging to structural group 9a. The structure of the gene encoding the shared precursor protein of the identified peptides was determined. One peptide, π-AnmTX Ugr 9a-1 (short name Ugr 9-1), produced a reversible inhibition effect on both the transient and the sustained current of human ASIC3 channels expressed in Xenopus laevis oocytes. It completely blocked the transient component (IC₅₀ 10 ± 0.6 μm) and partially (48 ± 2%) inhibited the amplitude of the sustained component (IC₅₀ 1.44 ± 0.19 μm). Using in vivo tests in mice, Ugr 9-1 significantly reversed inflammatory and acid-induced pain. The other two novel peptides, AnmTX Ugr 9a-2 (Ugr 9-2) and AnmTX Ugr 9a-3 (Ugr 9-3), did not inhibit the ASIC3 current. NMR spectroscopy revealed that Ugr 9-1 has an uncommon spatial structure, stabilized by two S-S bridges, with three classical β-turns and twisted β-hairpin without interstrand disulfide bonds. This is a novel peptide spatial structure that we propose to name boundless β-hairpin.     

Towards lead compounds as anti-cancer agents via new phaeosphaeride A derivatives

New derivatives of phaeosphaeride A (PPA) were synthesized and characterized. Anti-tumor studies were carried out on the U937, HCT-116, PC3, MCF-7, A549, К562, NCI-H929, Jurkat, THP-1, RPMI8228 tumor cell lines, and on the HEF cell line. All the compounds synthesized were found to have better efficacy than PPA towards the tumor cell lines mentioned. Compound 6 (IC₅₀?=?0.59?±?0.27?µM) was observed to be 11 times more active than PPA (IC₅₀?=?6.5?±?0.30?µM) towards the NCI-H929 cell line, with a therapeutic index of 18. Compound 6 was determined to be over half and 16 times more active than etoposide towards the NCI-H929 (IC₅₀?=?0.9?±?0.05?µM) and A549 (IC₅₀?=?100?±?7.0?µM) cell lines, respectively.     

Holocene radiocarbon-dated sites in northeastern Siberia: issues of temporal frequency, reservoir age, and human-nature interaction

The existing corpus of data on radiocarbon dates for Holocene sites in Northeastern Siberia was used as proxy to reconstruct the chronology of human occupation of the region. The problem of reservoir age correction in the Bering Sea region complicated this task and this issue needs to be solved in order to obtain more reliable age determinations for coastal archaeological sites. Using a chronology built after excluding the questionable dates from the database, the major patterns of human population dynamics and their possible correlation with climatic fluctuations were examined. No direct relationship appears to exist between these two processes. Additional archaeological and paleo environmental work needs to be carried out in this region of the North.