The influence of native populations’ genetic history on the reconstruction of invasion routes: the case of a highly invasive aquatic species

Biological Invasions - Insufficient data on the origins of the first introduced propagule and the initial stages of invasion complicate the reconstruction of a species’ invasion history....     

Extracellular hemoglobin combined with an O2-generating material overcomes O2 limitation in the bioartificial pancreas

The bioartificial pancreas encapsulating pancreatic islets in immunoprotective hydrogel is a promising therapy for Type 1 diabetes. As pancreatic islets are highly metabolically active and exquisitely sensitive to hypoxia, maintaining O₂ supply after transplantation remains a major challenge. In this study, we address the O₂ limitation by combining silicone-encapsulated CaO₂ (silicone-CaO₂) to generate O₂ with an extracellular hemoglobin O₂-carrier coencapsulated with islets. We showed that the hemoglobin improved by 37% the O₂-diffusivity through an alginate hydrogel and displayed antioxidant properties neutralizing deleterious reactive O₂ species produced by silicone-CaO₂. While the hemoglobin alone failed to maintain alginate macroencapsulated neonate pig islets under hypoxia, silicone-CaO₂ alone or combined to the hemoglobin restored islet viability and insulin secretion and prevented proinflammatory metabolism (PTGS2 expression). Interestingly, the combination took the advantages of the two individual strategies, improved neonate pig islet viability and insulin secretion in normoxia, and VEGF secretion and PDK1 normalization in hypoxia. Moreover, we confirmed the specific benefits of the combination compared to silicone-CaO₂ alone on murine pseudo-islet viability in normoxia and hypoxia. For the first time, our results show the interest of combining an O₂ provider with hemoglobin as an effective strategy to overcome O₂ limitations in tissue engineering.     

Structural investigation of the complexation properties between horse spleen apoferritin and metalloporphyrins

Crystallographic studies of L-chain horse spleen apoferritin (HSF) co-crystallized with Pt-hematoporphyrin IX and Sn-protoporphyrin IX have brought significant new insights into structure-function relationships in ferritins. Interactions of HSF with porphyrins are discussed. Structural results show that the nestling properties into HSF are dependent on the porphyrin moiety. (Only protoporphyrin IX significantly interacts with the protein, whereas hematoporphyrin IX does not.) These studies additionally point out the L-chain HSF ability to demetalate metalloporphyrins, a result which is of importance in looking at the iron storage properties of ferritins. In both compound investigated (whether the porphyrin reaches the binding site or not), the complexation appears to be concomitant with the extraction of the metal from the porphyrin. To analyze further the previous results, a three-dimensional alignment of ferritin sequences based on available crystallographic coordinates, including the present structures, is given. It confirms a high degree of homology between these members of the ferritin family and thus allows us to emphasize observed structural differences: 1) unlike L-chain HSF, H-chain human ferritin presents no preformed binding site; and 2) despite the absence of axial ligands, and due to the demetalation, L-chain HSF is able to host protoporphyrin at a similar location to that naturally found in bacterioferritin.     

Electronic tags for the tracking of insects in flight: effect of weight on flight performance of adult Colorado potato beetles

The wing loading of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), was found to decrease slightly with increasing size over a wide range of individual sizes and independent of sex. This makes it possible to use tags of the same weight for beetles of all sizes and suggests that if the addition of light electronic tags has any effect on the beetle's flight it will be similar across beetle size. The wing loading of individual potato beetles ranged from an average minimum 10.9 N m^–2 to an average maximum of 15.6 N m^–2 as their weights fluctuated over time following water and food uptake or dispersal. However, tests carried out in flight chambers indicate that beetles become incapable of upward flight as they go beyond an average wing loading of 11.8 N m^–2, that is 101 N (10.3 mg) beyond their minimum weight. It is estimated from our results that electronic tags should weigh no more than 23–33% of the potato beetle's acceptable extra loading for the technique to have no or minimal impact on the number and quality of upward flights taken.     

X-ray structure of TMP kinase from Mycobacterium tuberculosis complexed with TMP at 1.95 A resolution

The X-ray structure of Mycobacterium tuberculosis TMP kinase at 1.95 A resolution is described as a binary complex with its natural substrate TMP. Its main features involve: (i) a clear magnesium-binding site; (ii) an alpha-helical conformation for the so-called LID region; and (iii) a high density of positive charges in the active site. There is a network of interactions involving highly conserved side-chains of the protein, the magnesium ion, a sulphate ion mimicking the beta phosphate group of ATP and the TMP molecule itself. All these interactions conspire in stabilizing what appears to be the closed form of the enzyme. A complete multialignment of all (32) known sequences of TMP kinases is presented. Subtle differences in the TMP binding site were noted, as compared to the Escherichia coli, yeast and human enzyme structures, which have been reported recently. These differences could be used to design specific inhibitors of this essential enzyme of nucleotide metabolism. Two cases of compensatory mutations were detected in the TMP binding site of eukaryotic and prokaryotic enzymes. In addition, an intriguing high value of the electric field is reported in the vicinity of the phosphate group of TMP and the putative binding site of the gamma phosphate group of ATP.     

Pyridoxal 5'-phosphate inactivates DNA topoisomerase IB by modifying the lysine general acid

The present results demonstrate that pyridoxal, pyridoxal 5′-phosphate (PLP) and pyridoxal 5′-diphospho-5′-adenosine (PLP-AMP) inhibit Candida guilliermondii and human DNA topoisomerases I in forming an aldimine with the ε-amino group of an active site lysine. PLP acts as a competitive inhibitor of C.guilliermondii topoisomerase I (K_i = 40 μM) that blocks the cleavable complex formation. Chemical reduction of PLP-treated enzyme reveals incorporation of 1 mol of PLP per mol of protein. The limited trypsic proteolysis releases a 17 residue peptide bearing a lysine-bound PLP (KPPNTVIFDFLGK^*DSIR). Targeted lysine (K^*) in C.guilliermondii topoisomerase I corresponds to that found in topoisomerase I of Homo sapiens (K₅₃₂), Candida albicans (K₄₆₈), Saccharomyces cerevisiae (K₄₅₈) and Schizosaccharomyces pombe (K₅₀₅). In the human enzyme, K₅₃₂, belonging to the active site acts as a general acid catalyst and is therefore essential for activity. The spatial orientation of K₅₃₂–PLP within the active site was approached by molecular modeling using available crystallographic data. The PLP moiety was found at close proximity of several active residues. PLP could be involved in the cellular control of topoisomerases IB. It constitutes an efficient tool to explore topoisomerase IB dynamics during catalysis and is also a lead for new drugs that trap the lysine general acid.     

Signatures of cinnamyl alcohol dehydrogenase deficiency in poplar lignins

A series of transgenic poplars down-regulated for cinnamyl alcohol dehydrogenase (CAD) was analyzed by thioacidolysis. Among the lignin-derived monomers, the indene compounds that were recently shown to originate from sinapaldehyde incorporated into lignins through 8-O-4-cross-coupling, were found to increase as a function of CAD deficiency level. While these syringyl markers were recovered in substantial amounts in the most severely depressed lines, the markers for coniferaldehyde incorporation were recovered in only low amounts. In conjunction with these additional sinapaldehyde units and relative to the control samples, lignins in CAD-deficient poplar lines had less conventional syringyl-units and beta-O-4-bonds and more free phenolic groups. We found that almost half of the polymers in the most deficient lines could be solubilized in alkali and at room temperature. This unusual behavior suggests that lignins in CAD-deficient poplars occur as small, alkali-leachable lignin domains. That mainly sinapaldehyde incorporates into the lignins of CAD-deficient poplars suggests that the recently identified sinapyl alcohol dehydrogenase (SAD), which is structurally distinct from the CAD enzyme targeted herein, does not play any substantial role in constitutive lignification in poplar.