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991.
Fearnside JF Dumas ME Rothwell AR Wilder SP Cloarec O Toye A Blancher C Holmes E Tatoud R Barton RH Scott J Nicholson JK Gauguier D 《PloS one》2008,3(2):e1668
Insulin resistance plays a central role in type 2 diabetes and obesity, which develop as a consequence of genetic and environmental factors. Dietary changes including high fat diet (HFD) feeding promotes insulin resistance in rodent models which present useful systems for studying interactions between genetic background and environmental influences contributing to disease susceptibility and progression. We applied a combination of classical physiological, biochemical and hormonal studies and plasma (1)H NMR spectroscopy-based metabonomics to characterize the phenotypic and metabotypic consequences of HFD (40%) feeding in inbred mouse strains (C57BL/6, 129S6, BALB/c, DBA/2, C3H) frequently used in genetic studies. We showed the wide range of phenotypic and metabonomic adaptations to HFD across the five strains and the increased nutrigenomic predisposition of 129S6 and C57BL/6 to insulin resistance and obesity relative to the other strains. In contrast mice of the BALB/c and DBA/2 strains showed relative resistance to HFD-induced glucose intolerance and obesity. Hierarchical metabonomic clustering derived from (1)H NMR spectral data of the strains provided a phylometabonomic classification of strain-specific metabolic features and differential responses to HFD which closely match SNP-based phylogenetic relationships between strains. Our results support the concept of genomic clustering of functionally related genes and provide important information for defining biological markers predicting spontaneous susceptibility to insulin resistance and pathological adaptations to fat feeding. 相似文献
992.
Christopher W. Dick Olivier J. Hardy F. Andrew Jones Rémy J. Petit 《Tropical plant biology》2008,1(1):20-33
Gene flow via seed and pollen is a primary determinant of genetic and species diversity in plant communities at different spatial scales. This paper reviews studies of gene flow and population genetic structure in tropical rain forest trees and places them in ecological and biogeographic context. Although much pollination is among nearest neighbors, an increasing number of genetic studies report pollination ranging from 0.5–14 km for canopy tree species, resulting in extensive breeding areas in disturbed and undisturbed rain forest. Direct genetic measures of seed dispersal are still rare; however, studies of fine scale spatial genetic structure (SGS) indicate that the bulk of effective seed dispersal occurs at local scales, and we found no difference in SGS (Sp statistic) between temperate (N?=?24 species) and tropical forest trees (N?=?15). Our analysis did find significantly higher genetic differentiation in tropical trees (F ST?=?0.177; N?=?42) than in temperate forest trees (F ST?=?0.116; N?=?82). This may be due to the fact that tropical trees experience low but significant rates of self-fertilization and bi-parental inbreeding, whereas half of the temperate tree species in our survey are wind pollinated and are more strictly allogamous. Genetic drift may also be more pronounced in tropical trees due to the low population densities of most species. 相似文献
993.
Chandor-Proust A Berteau O Douki T Gasparutto D Ollagnier-de-Choudens S Fontecave M Atta M 《The Journal of biological chemistry》2008,283(52):36361-36368
The major DNA photoproduct in UV-irradiated Bacillus subtilis spores is the thymine dimer named spore photoproduct (SP, 5-(alpha-thyminyl)-5,6-dihydrothymine). The SP lesion has been found to be efficiently repaired by SP lyase (SPL) a very specific enzyme that reverses the SP to two intact thymines, at the origin of the great resistance of the spores to UV irradiation. SPL belongs to a superfamily of [4Fe-4S] iron-sulfur enzymes, called "Radical-SAM." Here, we show that the single substitution of cysteine 141 into alanine, a residue fully conserved in Bacillus species and previously shown to be essential for spore DNA repair in vivo, has a major impact on the outcome of the SPL-dependent repair reaction in vitro. Indeed the modified enzyme catalyzes the almost quantitative conversion of the SP lesion into one thymine and one thymine sulfinic acid derivative. This compound results from the trapping of the allyl-type radical intermediate by dithionite, used as reducing agent in the reaction mixture. Implications of the data reported here regarding the repair mechanism and the role of Cys-141 are discussed. 相似文献
994.
Jacquet E Girard JM Ramaen O Pamlard O Lévaique H Betton JM Dassa E Chesneau O 《The Journal of biological chemistry》2008,283(37):25332-25339
In Gram-positive bacteria, a large subfamily of dual ATP-binding cassette proteins confers acquired or intrinsic resistance to macrolide, lincosamide, and streptogramin antibiotics by a far from well understood mechanism. Here, we report the first biochemical characterization of one such protein, Vga(A), which is involved in streptogramin A (SgA) resistance among staphylococci. Vga(A) is composed of two nucleotide-binding domains (NBDs), separated by a charged linker, with a C-terminal extension and without identified transmembrane domains. Highly purified Vga(A) displays a strong ATPase activity (K(m) = 78 mum, V(m) = 6.8 min(-1)) that was hardly inhibited by orthovanadate. Using mutants of the conserved catalytic glutamate residues, the two NBDs of Vga(A) were shown to contribute unequally to the total ATPase activity, the mutation at NBD2 being more detrimental than the other. ATPase activity of both catalytic sites was essential for Vga(A) biological function because each single Glu mutant was unable to confer SgA resistance in the staphylococcal host. Of great interest, Vga(A) ATPase was specifically inhibited in a non-competitive manner by the SgA substrate, pristinamycin IIA (PIIA). A deletion of the last 18 amino acids of Vga(A) slightly affected the ATPase activity without modifying the PIIA inhibition values. In contrast, this deletion reduced 4-fold the levels of SgA resistance. Altogether, our results suggest a role for the C terminus in regulation of the SgA antibiotic resistance mechanism conferred by Vga(A) and demonstrate that this dual ATP-binding cassette protein interacts directly and specifically with PIIA, its cognate substrate. 相似文献
995.
Benjdia A Subramanian S Leprince J Vaudry H Johnson MK Berteau O 《The Journal of biological chemistry》2008,283(26):17815-17826
Sulfatases are a major group of enzymes involved in many critical physiological processes as reflected by their broad distribution in all three domains of life. This class of hydrolases is unique in requiring an essential post-translational modification of a critical active-site cysteine or serine residue to C(alpha)-formylglycine. This modification is catalyzed by at least three nonhomologous enzymatic systems in bacteria. Each enzymatic system is currently considered to be dedicated to the modification of either cysteine or serine residues encoded in the sulfatase-active site and has been accordingly categorized as Cys-type and Ser-type sulfatase-maturating enzymes. We report here the first detailed characterization of two bacterial anaerobic sulfatase-maturating enzymes (anSMEs) that are physiologically responsible for either Cys-type or Ser-type sulfatase maturation. The activity of both enzymes was investigated in vivo and in vitro using synthetic substrates and the successful purification of both enzymes facilitated the first biochemical and spectroscopic characterization of this class of enzyme. We demonstrate that reconstituted anSMEs are radical S-adenosyl-l-methionine enzymes containing a redox active [4Fe-4S](2+,+) cluster that initiates the radical reaction by binding and reductively cleaving S-adenosyl-l-methionine to yield 5 '-deoxyadenosine and methionine. Surprisingly, our results show that anSMEs are dual substrate enzymes able to oxidize both cysteine and serine residues to C(alpha)-formylglycine. Taken together, the results support a radical modification mechanism that is initiated by hydrogen abstraction from a serine or cysteine residue located in an appropriate target sequence. 相似文献
996.
Capendeguy O Iwaszkiewicz J Michielin O Horisberger JD 《The Journal of biological chemistry》2008,283(41):27850-27858
Na,K-ATPase is the main active transport system that maintains the large gradients of Na(+) and K(+) across the plasma membrane of animal cells. The crystal structure of a K(+)-occluding conformation of this protein has been recently published, but the movements of its different domains allowing for the cation pumping mechanism are not yet known. The structure of many more conformations is known for the related calcium ATPase SERCA, but the reliability of homology modeling is poor for several domains with low sequence identity, in particular the extracellular loops. To better define the structure of the large fourth extracellular loop between the seventh and eighth transmembrane segments of the alpha subunit, we have studied the formation of a disulfide bond between pairs of cysteine residues introduced by site-directed mutagenesis in the second and the fourth extracellular loop. We found a specific pair of cysteine positions (Y308C and D884C) for which extracellular treatment with an oxidizing agent inhibited the Na,K pump function, which could be rapidly restored by a reducing agent. The formation of the disulfide bond occurred preferentially under the E2-P conformation of Na,K-ATPase, in the absence of extracellular cations. Using recently published crystal structure and a distance constraint reproducing the existence of disulfide bond, we performed an extensive conformational space search using simulated annealing and showed that the Tyr(308) and Asp(884) residues can be in close proximity, and simultaneously, the SYGQ motif of the fourth extracellular loop, known to interact with the extracellular domain of the beta subunit, can be exposed to the exterior of the protein and can easily interact with the beta subunit. 相似文献
997.
998.
CE-SSCP and CE-FLA, simple and high-throughput alternatives for fungal diversity studies 总被引:2,自引:0,他引:2
Zinger L Gury J Alibeu O Rioux D Gielly L Sage L Pompanon F Geremia RA 《Journal of microbiological methods》2008,72(1):42-53
Fungal communities are key components of soil, but the study of their ecological significance is limited by a lack of appropriated methods. For instance, the assessment of fungi occurrence and spatio-temporal variation in soil requires the analysis of a large number of samples. The molecular signature methods provide a useful tool to monitor these microbial communities and can be easily adapted to capillary electrophoresis (CE) allowing high-throughput studies. Here we assess the suitability of CE-FLA (Fragment Length Polymorphism, denaturing conditions) and CE-SSCP (Single-Stranded Conformation Polymorphism, native conditions) applied to environmental studies since they require a short molecular marker and no post-PCR treatments. We amplified the ITS1 region from 22 fungal strains isolated from an alpine ecosystem and from total genomic DNA of alpine and infiltration basin soils. The CE-FLA and CE-SSCP separated 17 and 15 peaks respectively from a mixture of 19 strains. For the alpine soil-metagenomic DNA, the FLA displayed more peaks than the SSCP and the converse result was found for infiltration basin sediments. We concluded that CE-FLA and CE-SSCP of ITS1 region provided complementary information. In order to improve CE-SSCP sensitivity, we tested its resolution according to migration temperature and found 32 degrees C to be optimal. Because of their simplicity, quickness and reproducibility, we found that these two methods were promising for high-throughput studies of soil fungal communities. 相似文献
999.
Sulphur-oxidizing extracellular bacteria in the gills of Mytilidae associated with wood falls 总被引:1,自引:0,他引:1
Six morphotypes of small mussels (Bivalvia: Mytilidae) were found attached to naturally sunken wood collected in the Bohol Sea (Philippines). These specimens are related to the large Bathymodiolus mussels that are found worldwide at cold seeps and hydrothermal vents. In these habitats, the mytilids harbour sulphur- and methane-oxidizing endosymbionts in their gills and depend on the energy and carbon provided by the symbionts. In this study, bacteria associated with the gills of wood-associated mussels are characterized using molecular and microscopic techniques. The existence of bacteria in the lateral zone of gill filaments in all specimens is demonstrated. Comparative analyses of 16S rRNA gene and adenosine 5'-phosphosulphate (APS) reductase gene sequences indicate that the bacteria are closely related to sulphur-oxidizing endosymbionts of Bathymodiolus. FISHs using specific probes confirm that sulphur oxidizers are by far the most abundant, if not the only bacteria present. Electron micrographs displayed mostly extracellular bacteria located between microvilli at the apical surface of host gill epithelial cells all along the lateral zone of each gill filament. In some specimens, occasional occurrence of intracellular bacteria with similar morphology was noted. This study provides the first molecular evidence for the presence of possible thiotrophic symbiosis in sunken wood ecosystems. With their epibiotic bacteria, wood-associated mussels display a less integrated type of interaction than described in their seep, vent and whale fall relatives. 相似文献
1000.
RhoA/ROCK-mediated switching between Cdc42- and Rac1-dependent protrusion in MTLn3 carcinoma cells 总被引:1,自引:0,他引:1
El-Sibai M Pertz O Pang H Yip SC Lorenz M Symons M Condeelis JS Hahn KM Backer JM 《Experimental cell research》2008,314(7):1540-1552
Rho GTPases are versatile regulators of cell shape that act on the actin cytoskeleton. Studies using Rho GTPase mutants have shown that, in some cells, Rac1 and Cdc42 regulate the formation of lamellipodia and filopodia, respectively at the leading edge, whereas RhoA mediates contraction at the rear of moving cells. However, recent reports have described a zone of RhoA/ROCK activation at the front of cells undergoing motility. In this study, we use a FRET-based RhoA biosensor to show that RhoA activation localizes to the leading edge of EGF-stimulated cells. Inhibition of Rho or ROCK enhanced protrusion, yet markedly inhibited cell motility; these changes correlated with a marked activation of Rac-1 at the cell edge. Surprisingly, whereas EGF-stimulated protrusion in control MTLn3 cells is Rac-independent and Cdc42-dependent, the opposite pattern is observed in MTLn3 cells after inhibition of ROCK. Thus, Rho and ROCK suppress Rac-1 activation at the leading edge, and inhibition of ROCK causes a switch between Cdc42 and Rac-1 as the dominant Rho GTPase driving protrusion in carcinoma cells. These data describe a novel role for Rho in coordinating signaling by Rac and Cdc42. 相似文献