Homology modeling and molecular dynamics simulations of the N-terminal domain of wheat high molecular weight glutenin subunit 10

High molecular weight glutenin subunits (HMW-GS) are of a particular interest because of their biomechanical properties, which are important in many food systems such as breadmaking. Using fold-recognition techniques, we identified a fold compatible with the N-terminal domain of HMW-GS Dy10. This fold corresponds to the one adopted by proteins belonging to the cereal inhibitor family. Starting from three known protein structures of this family as templates, we built three models for the N-terminal domain of HMW-GS Dy10. We analyzed these models, and we propose a number of hypotheses regarding the N-terminal domain properties that can be tested experimentally. In particular, we discuss two possible ways of interaction between the N-terminal domains of the y-type HMW glutenin subunits. The first way consists in the creation of interchain disulfide bridges. According to our models, we propose two plausible scenarios: (1) the existence of an intrachain disulfide bridge between cysteines 22 and 44, leaving the three other cysteines free of engaging in intermolecular bonds; and (2) the creation of two intrachain disulfide bridges (involving cysteines 22-44 and cysteines 10-55), leaving a single cysteine (45) for creating an intermolecular disulfide bridge. We discuss these scenarios in relation to contradictory experimental results. The second way, although less likely, is nevertheless worth considering. There might exist a possibility for the N-terminal domain of Dy10, Nt-Dy10, to create oligomers, because homologous cereal inhibitor proteins are known to exist as monomers, homodimers, and heterooligomers. We also discuss, in relation to the function of the cereal inhibitor proteins, the possibility that this N-terminal domain has retained similar inhibitory functions.     

Variable male potential rate of reproduction: high male mating capacity as an adaptation to parasite-induced excess of females?

Numerous animals are known to harbour intracytoplasmic symbionts that gain transmission to a new host generation via female eggs and not male sperm. Bacteria of the genus Wolbachia are a typical example. They infect a large range of arthropod species and manipulate host reproduction in several ways. In terrestrial isopods (woodlice), Wolbachia are responsible for converting males into females (feminization (F)) in some species, or for infertility in certain host crosses in other species (cytoplasmic incompatibility (CI)). Wolbachia with the F phenotype impose a strong excess of females on their host populations, while Wolbachia expressing CI do not. Here, we test the possibility that male mating capacity (MC) is correlated with Wolbachia-induced phenotype. We show that males of isopod hosts harbouring F Wolbachia possess a strong MC (i.e. are able to mate with several females in a short time), while those of species harbouring CI Wolbachia possess a weaker MC. This pattern may be explained either by the selection of high MC following the increase in female-biased sex ratios, or because the F phenotype would lead to population extinction in species where MC is not sufficiently high. This last hypotheses is nevertheless more constrained by population structure.     

Decline of North Atlantic eels: a fatal synergy?

Panmictic species pose particular problems for conservation because their welfare can be addressed effectively only on a global scale. We recently documented by means of microsatellite analysis that the European eel (Anguilla anguilla) is not panmictic but instead shows genetic isolation by distance. In this study, we extended the analysis to the American eel (A. rostrata) by applying identical analytical procedures and statistical power. Results obtained for the American eel were in sharp contrast with those obtained for the European eel: the null hypothesis of panmixia could not be rejected, and no isolation by distance was detected. This implies that the species must be managed as a single population. Using Bayesian statistics, we also found that the effective population sizes for both species were surprisingly low and that the populations had undergone severe contractions, most probably during the Wisconsinan glaciation. The apparent sensitivity of eels to climatic changes affecting the strength and position of the Gulf Stream 20,000 years ago is particularly worrying, given the effects of the ongoing global warming on the North Atlantic climate. Moreover, additional short-term stresses such as surging glass eel prizes, overfishing and lethal parasitic infections negatively affect eel population size. The fascinating transatlantic migration and life cycle of Atlantic eels is also their Achilles' heel as these negative short- and long-term effects will probably culminate in a fatal synergy if drastic conservation measures are not implemented to protect these international biological resources.     

Parallel liquid synthesis of N,N'-Disubstituted 3-amino azepin-2-ones as potent and specific farnesyl transferase inhibitors

A rapid structure-activity study was performed by parallel liquid synthesis on N,N'-disubstitution of 3-amino azepin-2-one to afford potent and specific farnesyl transferase inhibitors with low nM enzymatic and cellular activities. The activities of the selected compounds were validated in vivo, and compounds 41a and 44a presented significant antitumour activity.     

Mg-nucleotides induced dissociation of liposome-bound creatine kinase: reversible changes in its secondary structure and in the fluidity of the bilayer

MgADP binding to mitochondrial creatine kinase (mtCK) adsorbed on liposomes was induced by the photorelease of caged ADP. The nucleotide binding produced two types of structural changes. One was related to the well-established release of mtCK from the liposomes. The other corresponded to reversible structural changes induced by nucleotide binding to mtCK as demonstrated here. Infrared spectroscopy data show that the MgADP-induced desorption of mtCK from vesicles led to a slight increase in alpha-helix structures in mtCK at the expense of a small decrease in beta-sheet structures and a concomitant increase in the fluidity of the membranes. The desorption of mtCK induced by MgADP and MgATP was almost complete, as shown by centrifugation and enzymatic activity measurements. The photorelease of MgADP in a reactive medium containing phosphocreatine and mtCK associated with liposomes led to nucleotide binding and to the formation of MgATP and creatine. Addition of phosphocreatine also desorbed mtCK from liposomes, while addition of creatine did not. Interpretation of these results would suggest that ADP, ATP or phosphocreatine induce the release of mtCK from membranes, increase the phospholipid bilayer fluidity, and may also decrease the number of contact sites between inner and outer mitochondrial membranes, thus affecting the activity of other mitochondrial enzymes. It is tempting to propose that membrane mtCK binding regulation by nucleotide and PCr concentrations may serve as a physiological adaptation for energy supply.     

In vivo impact of CpG1826 oligodeoxynucleotide on CD8 T cell primary responses and survival

CpG oligodeoxynucleotide (ODN) promotes maturation of APCs in vivo and induces strong type 1 T cell responses in mice. In this study, we have investigated the ability of CpG1826 to modulate peptide-specific CD8 T cell responses in a context where CD4 T cells are likely to play a minor role. The effects of CpG1826 were evaluated in a system where a population of NP68-specific F5 TCR transgenic CD8 T cells is diluted into a polyclonal host following adoptive transfer into C57BL/10 syngeneic recipients. Using this approach, we found that CpG1826 enhanced the ability of F5 CD8 T cells to undergo multiple divisions in vivo, to express IFN-gamma ex vivo, and to up-regulate memory-associated cell surface markers such as CD122 (IL-2Rbeta) and Ly-6C. Moreover, CpG1826 greatly increased in vivo cytotoxic activity. Using tetramer detection, we found that CpG1826 promoted long-term survival of Ag-specific CD8 T cells after immunization while no NP68-specific cells were detected when the cognate peptide was injected alone. These results indicate that CpG1826 acts as an adjuvant which increases CD8 T cell effector responses and promotes long-term survival of NP68 peptide-specific cells in vivo. They also suggest that this adjuvant can modulate CD8 T cell responses in a system which is likely to be independent of CD4 T cell help.     

Candida albicans phospholipomannan promotes survival of phagocytosed yeasts through modulation of bad phosphorylation and macrophage apoptosis

The surface of the pathogenic yeast Candida albicans is coated with phospholipomannan (PLM), a phylogenetically unique glycolipid composed of beta-1,2-oligomannosides and phytoceramide. This study compared the specific contribution of PLM to the modulation of signaling pathways linked to the survival of C. albicans in macrophages in contrast to Saccharomyces cerevisiae. C. albicans endocytosis by J774 and disregulation of the ERK1/2 signal transduction pathway was associated downstream with a reduction in Bad Ser-112 phosphorylation and disappearance of free Bcl-2. This suggested an apoptotic effect, which was confirmed by staining of phosphatidylserine in the macrophage outer membrane. The addition of PLM to macrophages incubated with S. cerevisiae mimicked each of the disregulation steps observed with C. albicans and promoted the survival of S. cerevisiae. Externalization of membranous phosphatidylserine, loss of mitochondrial integrity, and DNA fragmentation induced by PLM showed that this molecule promoted yeast survival by inducing host cell death. These findings suggest strongly that PLM is a virulence attribute of C. albicans and that elucidation of the relationship between structure and apoptotic activity is an innovative field of research.