Role of nucleotide hydrolysis in the polymerization of actin and tubulin

Here is presented a short survey of the main aspects of the involvement of nucleotide hydrolysis in the polymerization of actin and microtubules: 1) XTP hydrolysis is not tightly coupled to the polymerization process; XTP hydrolysis and phosphate release generate an unstable XDP-polymer which is maintained at steady state, in the presence of XTP, by terminal XTP-subunits; this feature can generate patterns of phase transitions of the polymer between stable and unstable conformations; 2) Interactions between subunits are involved in the mechanism of XTP hydrolysis; 3) XTP cleavage on the polymer is followed by the slow release of P_i; the structural and thermodynamic characteristics of the transient XDP-P_i-polymer may play a crucial role in the regulation of the dynamics of microtubules and actin filaments.     

Contribution a l'étude desAphelinidae aphidiphages et de leurs hotes en France [Hym. Chalcidoidea]

Résumé L'auteur donne un nouvel exemple de variabilité de la pigmentation chez un Aphelinide. L'inventaire des Aphelinides de France est dressé; 26 h?tes nouveaux sont précisés. L'observation du comportement de plusieurs espèces d'Aphelinides dans la nature a révélé l'importance du facteur de l'humidité ambiante pour l'apparition de taux de parasitisme élevés.

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Summary New data on the pigmentation variability byA. chaonia Wlk. (Aphelinidae) under natural conditions are given. The provisional list of the 11 species ofAphelinidae collected in France till now includesAphelinus flavipes Foerster andA. varipes Foerster, two species not recorded before in this country; 26 new hosts are recorded as parasites of 6 species ofAphelinus. Field observations on several Aphelinids emphasize the importance of the high level of surrounding humidity to determine high parasitism rates.

     

Exploration of the core metabolism of symbiotic bacteria

ABSTRACT: BACKGROUND: A large number of genome-scale metabolic networks is now available for many organisms, mostly bacteria. Previous works on minimal gene sets, when analysing host-dependent bacteria, found small common sets of metabolic genes. When such analyses are restricted to bacteria with similar lifestyles, larger portions of metabolism are expected to be shared and their composition is worth investigating. Here we report a comparative analysis of the small molecule metabolism of symbiotic bacteria, exploring common and variable portions as well as the contribution of different lifestyle groups to the reduction of a common set of metabolic capabilities. RESULTS: We found no reaction shared by all the bacteria analysed. Disregarding those with the smallest genomes, we still do not find a reaction core, however we did find a core of biochemical capabilities. While obligate intracellular symbionts have no core of reactions within their group, extracellular and cell-associated symbionts do have a small core composed of disconnected fragments. In agreement with previous findings in Escherichia coli, their cores are enriched in biosynthetic processes whereas the variable metabolisms have similar ratios of biosynthetic and degradation reactions. Conversely, the variable metabolism of obligate intracellular symbionts is enriched in anabolism. CONCLUSION: Even when removing the symbionts with the most reduced genomes, there is no core of reactions common to the analysed symbiotic bacteria. The main reason is the very high specialisation of obligate intracellular symbionts, however, host-dependence alone is not an explanation for such absence. The composition of the metabolism of cell-associated and extracellular bacteria shows that while they have similar needs in terms of the building blocks of their cells, they have to adapt to very distinct environments. On the other hand, in obligate intracellular bacteria, catabolism has largely disappeared, whereas synthetic routes appear to have been selected for depending on the nature of the symbiosis. As more genomes are added, we expect, based on our simulations, that the core of cell-associated and extracellular bacteria continues to diminish, converging to approximately 60 reactions.     

A Biomimetic Collagen Derived Peptide Exhibits Anti-Angiogenic Activity in Triple Negative Breast Cancer

We investigated the application of a mimetic 20 amino acid peptide derived from type IV collagen for treatment of breast cancer. We showed that the peptide induced a decrease of proliferation, adhesion, and migration of endothelial and tumor cells in vitro. We also observed an inhibition of triple negative MDA-MB-231 xenograft growth by 75% relative to control when administered intraperitoneally for 27 days at 10 mg/kg. We monitored in vivo the changes in vascular properties throughout the treatment using MRI and found that the vascular volume and permeability surface area product decreased significantly. The treatment also resulted in an increase of caspase-3 activity and in a reduction of microvascular density. The multiple mode of action of this peptide, i.e., anti-angiogenic, and anti-tumorigenic, makes it a viable candidate as a therapeutic agent as a monotherapy or in combination with other compounds.