Domain 3 of NS5A protein from the hepatitis C virus has intrinsic alpha-helical propensity and is a substrate of cyclophilin A

Nonstructural protein 5A (NS5A) is essential for hepatitis C virus (HCV) replication and constitutes an attractive target for antiviral drug development. Although structural data for its in-plane membrane anchor and domain D1 are available, the structure of domains 2 (D2) and 3 (D3) remain poorly defined. We report here a comparative molecular characterization of the NS5A-D3 domains of the HCV JFH-1 (genotype 2a) and Con1 (genotype 1b) strains. Combining gel filtration, CD, and NMR spectroscopy analyses, we show that NS5A-D3 is natively unfolded. However, NS5A-D3 domains from both JFH-1 and Con1 strains exhibit a propensity to partially fold into an α-helix. NMR analysis identifies two putative α-helices, for which a molecular model could be obtained. The amphipathic nature of the first helix and its conservation in all genotypes suggest that it might correspond to a molecular recognition element and, as such, promote the interaction with relevant biological partner(s). Because mutations conferring resistance to cyclophilin inhibitors have been mapped into NS5A-D3, we also investigated the functional interaction between NS5A-D3 and cyclophilin A (CypA). CypA indeed interacts with NS5A-D3, and this interaction is completely abolished by cyclosporin A. NMR heteronuclear exchange experiments demonstrate that CypA has in vitro peptidyl-prolyl cis/trans-isomerase activity toward some, but not all, of the peptidyl-prolyl bonds in NS5A-D3. These studies lead to novel insights into the structural features of NS5A-D3 and its relationships with CypA.     

Benzo[f]naphtyridones: a new family of topical antibacterial agents active on multi-resistant Gram-positive pathogens

The synthesis and antibacterial activity of benzo[f][1,7]naphtyridone derivatives are reported. These compounds are potent antibacterial agents with a Gram-positive spectrum of activity. They are active against multi-resistant cocci, especially Staphylococcus aureus strains. Their physico-chemical and biological properties make them particularly suitable for topical antibacterial use.     

Modulation of TRPV4 gating by intra- and extracellular Ca2+

We have studied the modulation of gating properties of the Ca2+-permeable, cation channel TRPV4 transiently expressed in HEK293 cells. The phorbol ester 4alphaPDD transiently activated a current through TRPV4 in the presence of extracellular Ca2+. Increasing the concentration of extracellular Ca2+ ([Ca2+](e)) reduced the current amplitude and accelerated its decay. This decay was dramatically delayed in the absence of [Ca2+](e). It was also much slower in the presence of [Ca2+](e) in a mutant channel, obtained by a point mutation in the 6th transmembrane domain, F707A. Mutant channels, containing a single mutation in the C-terminus of TRPV4 (E797), were constitutively open. In conclusion, gating of the 4alphaPDD-activated TRPV4 channel depends on both extra- and intracellular Ca2+, and is modulated by mutations of single amino acid residues in the 6th transmembrane domain and the C-terminus of the TRPV4 protein.     

Crosstalk between nitric oxide and zinc pathways to neuronal cell death involving mitochondrial dysfunction and p38-activated K+ channels

Nitric oxide (NO) and zinc (Zn2+) are implicated in the pathogenesis of cerebral ischemia and neurodegenerative diseases. However, their relationship and the molecular mechanism of their neurotoxic effects remain unclear. Here we show that addition of exogenous NO or NMDA (to increase endogenous NO) leads to peroxynitrite (ONOO-) formation and consequent Zn2+ release from intracellular stores in cerebrocortical neurons. Free Zn2+ in turn induces respiratory block, mitochondrial permeability transition (mPT), cytochrome c release, generation of reactive oxygen species (ROS), and p38 MAP kinase activation. This pathway leads to caspase-independent K+ efflux with cell volume loss and apoptotic-like death. Moreover, Zn2+ chelators, ROS scavengers, Bcl-xL, dominant-interfering p38, or K+ channel blockers all attenuate NO-induced K+ efflux, cell volume loss, and neuronal apoptosis. Thus, these data establish a new form of crosstalk between NO and Zn2+ apoptotic signal transduction pathways that may contribute to neurodegeneration.     

Genetically Engineered Immunomodulatory Streptococcus thermophilus Strains Producing Antioxidant Enzymes Exhibit Enhanced Anti-Inflammatory Activities

The aims of this study were to develop strains of lactic acid bacteria (LAB) having both immunomodulatory and antioxidant properties and to evaluate their anti-inflammatory effects both in vitro, in different cellular models, and in vivo, in a mouse model of colitis. Different Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains were cocultured with primary cultures of mononuclear cells. Analysis of the pro- and anti-inflammatory cytokines secreted by these cells after coincubation with candidate bacteria revealed that L. delbrueckii subsp. bulgaricus CRL 864 and S. thermophilus CRL 807 display the highest anti-inflammatory profiles in vitro. Moreover, these results were confirmed in vivo by the determination of the cytokine profiles in large intestine samples of mice fed with these strains. S. thermophilus CRL 807 was then transformed with two different plasmids harboring the genes encoding catalase (CAT) or superoxide dismutase (SOD) antioxidant enzymes, and the anti-inflammatory effects of recombinant streptococci were evaluated in a mouse model of colitis induced by trinitrobenzenesulfonic acid (TNBS). Our results showed a decrease in weight loss, lower liver microbial translocation, lower macroscopic and microscopic damage scores, and modulation of the cytokine production in the large intestines of mice treated with either CAT- or SOD-producing streptococci compared to those in mice treated with the wild-type strain or control mice without any treatment. Furthermore, the greatest anti-inflammatory activity was observed in mice receiving a mixture of both CAT- and SOD-producing streptococci. The addition of L. delbrueckii subsp. bulgaricus CRL 864 to this mixture did not improve their beneficial effects. These findings show that genetically engineering a candidate bacterium (e.g., S. thermophilus CRL 807) with intrinsic immunomodulatory properties by introducing a gene expressing an antioxidant enzyme enhances its anti-inflammatory activities.     

Water deficit in field-grown Gossypium hirsutum primarily limits net photosynthesis by decreasing stomatal conductance,increasing photorespiration,and increasing the ratio of dark respiration to gross photosynthesis

Much effort has been expended to improve irrigation efficiency and drought tolerance of agronomic crops; however, a clear understanding of the physiological mechanisms that interact to decrease source strength and drive yield loss has not been attained. To elucidate the underlying mechanisms contributing to inhibition of net carbon assimilation under drought stress, three cultivars of Gossypium hirsutum were grown in the field under contrasting irrigation regimes during the 2012 and 2013 growing season near Camilla, Georgia, USA. Physiological measurements were conducted on three sample dates during each growing season (providing a broad range of plant water status) and included, predawn and midday leaf water potential (Ψ_PD and Ψ_MD), gross and net photosynthesis, dark respiration, photorespiration, and chlorophyll a fluorescence. End-of-season lint yield was also determined. Ψ_PD ranged from −0.31 to −0.95 MPa, and Ψ_MD ranged from −1.02 to −2.67 MPa, depending upon irrigation regime and sample date. G. hirsutum responded to water deficit by decreasing stomatal conductance, increasing photorespiration, and increasing the ratio of dark respiration to gross photosynthesis, thereby limiting P_N and decreasing lint yield (lint yield declines observed during the 2012 growing season only). Conversely, even extreme water deficit, causing a 54% decline in P_N, did not negatively affect actual quantum yield, maximum quantum yield, or photosynthetic electron transport. It is concluded that P_N is primarily limited in drought-stressed G. hirsutum by decreased stomatal conductance, along with increases in respiratory and photorespiratory carbon losses, not inhibition or down-regulation of electron transport through photosystem II. It is further concluded that Ψ_PD is a reliable indicator of drought stress and the need for irrigation in field-grown cotton.     

Analytic partitioning of honeybee (Apis mellifera L.) flight activity at nest entrance: adaptation and behavioural inertia in a changing environment

Ecology of bees (Hymenoptera, Apiformes) is entirely constrained by the centralized exchange between the nest and its environment. Herein, we investigate the ecological meaning of the flight activity of honeybees (Apis mellifera L.) at the entrance of the nest, and assessed whether this simple metric can be used as a proxy to infer on the colony state (population size and foraging activity). Theory predicts that flight activity of a colony should increase (1) with population size (density-dependence hypothesis), (2) with floral resource availability (optimal foraging hypothesis), and (3) with the flight activity during previous hours or days, due to a temporal autocorrelation (behavioural inertia hypothesis). We built and compared series of explanatory models for the flight activity measured at the entrance of hives, and its two visible components, namely bees with and without pollen loads. Data were collected on 26 honeybee colonies, both before and after a translocation into a new environment with controlled floral resource availability in order to distinguish among the respective contributions of explanatory factors. Current flight activity was consistently and positively influenced by previous flight activity as well as by the current resource availability. To our knowledge, this represents the first characterization of behavioural inertia in the context of a collective behaviour. Population size only influenced flight activity of bees without pollen loads. We discuss the limits of using simple counts of flying bees at the hive entrance to infer the colony state.     

The effect of drought stress on heterozygosity–fitness correlations in pedunculate oak (Quercus robur)

Background and Aims

The interaction between forest fragmentation and predicted climate change may pose a serious threat to tree populations. In small and spatially isolated forest fragments, increased homozygosity may directly affect individual tree fitness through the expression of deleterious alleles. Climate change-induced drought stress may exacerbate these detrimental genetic consequences of forest fragmentation, as the fitness response to low levels of individual heterozygosity is generally thought to be stronger under environmental stress than under optimal conditions.

Methods

To test this hypothesis, a greenhouse experiment was performed in which various transpiration and growth traits of 6-month-old seedlings of Quercus robur differing in multilocus heterozygosity (MLH) were recorded for 3 months under a well-watered and a drought stress treatment. Heterozygosity–fitness correlations (HFC) were examined by correlating the recorded traits of individual seedlings to their MLH and by studying their response to drought stress.

Key Results

Weak, but significant, effects of MLH on several fitness traits were obtained, which were stronger for transpiration variables than for the recorded growth traits. High atmospheric stress (measured as vapour pressure deficit) influenced the strength of the HFCs of the transpiration variables, whereas only a limited effect of the irrigation treatment on the HFCs was observed.

Conclusions

Under ongoing climate change, increased atmospheric stress in the future may strengthen the negative fitness responses of trees to low MLH. This indicates the necessity to maximize individual multilocus heterozygosity in forest tree breeding programmes.