Etude structurale de la Dihydroflavonol 4-Reductase, enzime clé de la biosynthèse des flavonoïdes chez Vitis Vinifera

Anthocyanes et tanins condensés constituent deux classes de flavonoïdes présentant des propriétés d’intérêt dans le domaine de la « vigne et du vin ». Non seulement, ils confèrent à la plante une forte résistance aux pathogènes mais ils sont de plus, très impliqués dans la qualité organoleptique du vin. Dans une première partie de ce mémoire, nous présentons une synthèse des connaissances se rapportant aux flavonoïdes. Nous décrivons les grandes classes de composés, leurs différentes propriétés ainsi que leur voie de biosynthèse. La seconde partie de ce travail est consacrée à l’étude tant fonctionnelle que structurale d’une enzyme, la dihydroflavonol 4-reductase de Vitis vinifera essentielle à la synthèse des anthocyanes et des tanins condensés. La structure 3D confirme l’importance du segment 131-156 qui délimite le site actif. Les résultats démontrent que le seul résidu 133 ne peut être tenu pour responsable de la spécificité de substrat. Ce travail ouvre la voie à une étude plus approfondie du rôle joué par les autres acides aminés appartenant au segment précédent.Anthocyanins and condensed tannins are two major classes of flavonoids presenting properties of interest in Viticulture and Oenology. Not only they are involved in relevant functions in the plant, such as protection against pathogens, but also they strongly influence the organoleptic properties of wine. In the first part of this manuscript, we present a review of what is known about flavonoids. We describe the different classes of compounds, their various properties, together with their biosynthetic pathway. The second part of the work deals with the functional and structural studies of dihydroflavonol 4-reductase from Vitis vinifera, a key enzyme in the anthocyanin and condensed tannin biosynthesis. The 3D structure confirms the importance of the 131-156 region which lines the substrate binding site. Results demonstrate that position 133 cannot be solely responsible for the substrate specificity. This work leads the way towards a more detailed investigation of the relevant functions of other amino acids included in the above region

Using magnetic disturbances to improve IMU-based position estimation

International audienceWe address the problem of position estimation for a rigid body using an inertial measurement unit (IMU). In this paper, we present a Kalman filtering technique which takes advantage of the magnetic disturbances usually observed indoors. This is an important topic for military operations in urban areas where GPS is often unavailable. This approach yields significant improvements in estimation accuracy. We illustrate our technique with several experimental results obtained with a low cost IMU

Iterative calibration method for inertial and magnetic sensors

International audienceWe address the problem of three-axis sensor calibration. Our focus is on magnetometers. Usual errors (misalignment, non-orthogonality, scale factors, biases) are accounted for. We consider a method where no specific calibration hardware is required. We solely use the fact that the norm of the sensed field must remain constant irrespective of the sensors orientation. The proposed algorithm is iterative. Its convergence is studied. Experiments conducted with MEMS sensors (magnetometers) stress the relevance of the approach

Similarities Between Proton and Neutron Induced Dark Current Distribution in CMOS Image Sensors

Several CMOS image sensors were exposed to neutron or proton beams (displacement damage dose range from 4 TeV/g to 1825 TeV/g) and their radiation-induced dark current distributions are compared. It appears that for a given displacement damage dose, the hot pixel tail distributions are very similar, if normalized properly. This behavior is observed on all the tested CIS designs (4 designs, 2 technologies) and all the tested particles (protons from 50 MeV to 500 MeV and neutrons from 14 MeV to 22 MeV). Thanks to this result, all the dark current distribution presented in this paper can be fitted by a simple model with a unique set of two factors (not varying from one experimental condition to another). The proposed normalization method of the dark current histogram can be used to compare any dark current distribution to the distributions observed in this work. This paper suggests that this model could be applied to other devices and/or irradiation conditions

Influence of displacement damage dose on dark current distributions of irradiated CMOS image sensors

Dark current increase distributions due to displacement damages are modeled using displacement damage dose concept. Several CMOS image sensors have been exposed to neutrons or protons and we have characterized their degradation in terms of dark current increase. We have been able to extract a set of two factors from the experimental dark current increase distributions. These factors are used to predict and build dark current increase distribution and leads to a better understanding of displacement damage effects on CMOS image sensors

Effect of nitrogen-rich cell culture surfaces on type X collagen expression by bovine growth plate chondrocytes

Background: Recent evidence indicates that osteoarthritis (OA) may be a systemic disease since mesenchymal stem cells (MSCs) from OA patients express type X collagen, a marker of late stage chondrocyte hypertrophy (associated with endochondral ossification). We recently showed that the expression of type X collagen was suppressed when MSCs from OA patients were cultured on nitrogen (N)-rich plasma polymer layers, which we call "PPE:N" (N-doped plasma-polymerized ethylene, containing up to 36 atomic percentage (at.%) of N.Methods: In the present study, we examined the expression of type X collagen in fetal bovine growth plate chondrocytes (containing hypertrophic chondrocytes) cultured on PPE:N. We also studied the effect of PPE: N on the expression of matrix molecules such as type II collagen and aggrecan, as well as on proteases (matrix metalloproteinase-13 (MMP-13) and molecules implicated in cell division (cyclin B2). Two other culture surfaces, "hydrophilic" polystyrene (PS, regular culture dishes) and nitrogen-containing cation polystyrene (Primaria (R)), were also investigated for comparison.Results: Results showed that type X collagen mRNA levels were suppressed when cultured for 4 days on PPE: N, suggesting that type X collagen is regulated similarly in hypertrophic chondrocytes and in human MSCs from OA patients. However, the levels of type X collagen mRNA almost returned to control value after 20 days in culture on these surfaces. Culture on the various surfaces had no significant effects on type II collagen, aggrecan, MMP-13, and cyclin B2 mRNA levels.Conclusion: Hypertrophy is diminished by culturing growth plate chondrocytes on nitrogen-rich surfaces, a mechanism that is beneficial for MSC chondrogenesis. Furthermore, one major advantage of such "intelligent surfaces" over recombinant growth factors for tissue engineering and cartilage repair is potentially large cost-saving

A genome scan for quantitative trait loci affecting the Salmonella carrier-state in the chicken

Selection for increased resistance to Salmonella colonisation and excretion could reduce the risk of foodborne Salmonella infection. In order to identify potential loci affecting resistance, differences in resistance were identified between the N and 61 inbred lines and two QTL research performed. In an F2 cross, the animals were inoculated at one week of age with Salmonella enteritidis and cloacal swabs were carried out 4 and 5 wk post inoculation (thereafter called CSW4F2 and CSW4F2) and caecal contamination (CAECF2) was assessed 1 week later. The animals from the (N × 61) × N backcross were inoculated at six weeks of age with Salmonella typhimurium and cloacal swabs were studied from wk 1 to 4 (thereafter called CSW1BC to CSW4BC). A total of 33 F2 and 46 backcross progeny were selectively genotyped for 103 and 135 microsatellite markers respectively. The analysis used least-squares-based and non-parametric interval mapping. Two genome-wise significant QTL were observed on Chromosome 1 for CSW2BC and on Chromosome 2 for CSW4F2, and four suggestive QTL for CSW5F2 on Chromosome 2, for CSW5F2 and CSW2BC on chromosome 5 and for CAECF2 on chromosome 16. These results suggest new regions of interest and the putative role of SAL1

Molecular basis of RNA guanine-7 methyltransferase (RNMT) activation by RAM

Maturation and translation of mRNA in eukaryotes requires the addition of the 7-methylguanosine cap. In vertebrates, the cap methyltransferase, RNA guanine-7 methyltransferase (RNMT), has an activating subunit, RNMT-Activating Miniprotein (RAM). Here we report the first crystal structure of the human RNMT in complex with the activation domain of RAM. A relatively unstructured and negatively charged RAM binds to a positively charged surface groove on RNMT, distal to the active site. This results in stabilisation of a RNMT lobe structure which co-evolved with RAM and is required for RAM binding. Structure-guided mutagenesis and molecular dynamics simulations reveal that RAM stabilises the structure and positioning of the RNMT lobe and the adjacent α-helix hinge, resulting in optimal positioning of helix A which contacts substrates in the active site. Using biophysical and biochemical approaches, we observe that RAM increases the recruitment of the methyl donor, AdoMet (S-adenosyl methionine), to RNMT. Thus we report the mechanism by which RAM allosterically activates RNMT, allowing it to function as a molecular rheostat for mRNA cap methylation