À l’heure actuelle, le paludisme reste un problème de santé majeur et demeure une des maladies parasitaires les plus menaçantes. Parmi les cinq espèces de malaria infectant l’homme, Plasmodium falciparum est la forme la plus mortelle. Lors de la phase érythrocytaire de son cycle de vie, causant tous les symptômes du paludisme, P.falciparum utilise les phospholipides pour créer les membranes nécessaires au développement de cellules filles. Chez P. falciparum, la phosphatidylcholine est principalement obtenue grâce à la voie de synthèse de novo, dite voie de Kennedy. Dans cette voie de biosynthèse, la seconde étape catalysée par la CTP:phosphocholine cytidylyltransferase [EC 2.7.7.15] est limitante et apparait essentielle pour la survie du parasite murin P. berghei lors de la phase sanguine. Les objectifs de mon travail de thèse ont été de caractériser structuralement cette enzyme et d’identifier des effecteurs, principalement grâce à des approches de « fragment-based drug design » (FBDD). Ainsi, la première structure cristalline du domaine catalytique de l’enzyme (PfCCT) a été déterminée avec une résolution de 2.2 Å. De plus, les structures de trois complexes enzyme-substrat (en présence de CMP, de phosphocholine ou de choline) et d’un complexe enzyme-produit (CDP-Choline) ont été déterminées. Ces structures cristallographiques apportent des informations détaillées sur la poche de liaison de l’enzyme et elles ont révélé des informations sur le mécanisme de la réaction catalytique à l’échelle atomique. La seconde partie de ma thèse présente les méthodes développées pour identifier des inhibiteurs potentiels de la PfCCT. Une approche de FBDD a été utilisée pour identifier et sélectionner de petites molécules (fragments, PM<300 Da) se liant à la PfCCT. Diverses techniques biophysiques (fluorescence-based thermal shift assay, différence de transfert de saturation par RMN, dénaturation chimique isotherme) ont permis la sélection de 23 fragments à partir du criblage d’une bibliothèque (~ 300 molécules). En parallèle, un criblage in silico de plus grandes bibliothèques de fragments (environ 15 000 composés) a permis d’identifier 100 fragments “hits”. Enfin, 5 composés déjà connus pour inhiber la croissance parasitaire (Malaria Box fournit par Medecines for Malaria Venture) ont été sélectionnés pour leur inhibition de l’activité de la PfCCT recombinante. L’ensemble de ces données ouvre la voie pour l’élaboration de futurs composés ciblant la PfCCT et inhibant la biosynthèse de phosphatidylcholine chez P. falciparum. / Malaria remains a major global health problem and the most threatening parasitic disease. Among the 5 malaria species that affect humans, Plasmodium falciparum is the most deadly form. During its life cycle, in erythrocytic stage, which causes all the malaria symptoms, P. falciparum relies on phospholipids to build the membranes necessary for daughter cell development. Approximately 85% of parasite phospholipids consist of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) synthesized by the parasite through the de novo Kennedy pathways. In the pathway of phosphatidylcholine biosynthesis, the second step catalyzed by CTP:phosphocholine cytidylyltransferase [EC 2.7.7.15] is rate limiting and appears essential for the parasite survival at its blood stage. In this PhD thesis I focus on the structural characterization of this enzyme and the identification of effectors mainly by fragment-based drug design approach (FBDD). The first reported crystal structure of the catalytic domain of the enzyme target (PfCCT) has been solved at resolution 2.2 Å. Four other crystal structures of PfCCT in complex with substrates (CMP, phosphocholine and choline) or product (CDP-choline) have been determined. These structural data give detailed images of the binding pocket and reveal the enzyme structures at all catalytic steps that provide crucial information on the catalytic mechanism at atomic level. The second part of the project present the methods developed to identify potential PfCCT inhibitors. A FBDD approach was used in order to identify and select small molecules (fragments, MW< 300 Da) binding to the PfCCT. A combination of biophysical techniques (fluorescence-based thermal shift assay, saturation transfer difference NMR and isothermal chemical denaturation) allowed the selection of 23 fragment hits from the screenings of fragment library (~ 300 molecules). In parallel in silico screening of larger fragment libraries (~15,000 compounds) resulted in 100 selected hits. Finally, 5 compounds already known to inhibit parasite growth (Malaria Box from Medicines for Malaria Venture) were selected for their inhibition of the recombinant PfCCT activity. The results obtained within this thesis brought important knowledge and structural insights on the catalytic mechanism of PfCCT. Taken together, these results pave the way for future structure-based drug design to target PfCCT and to inhibit the essential phosphatidylcholine biosynthesis in P. falciparum.

Deciphering the activity of chemical molecules against a pathogenic organism is an essential task in drug discovery process. Virtual screening, in which few plausible molecules are selected from a large set for further processing using computational methods, has become an integral part and complements the expensive and time-consuming in vivo and in vitro experiments. To this end, it is essential to extract certain features from molecules which in the one hand are relevant to the biological activity under consideration, and on the other are suitable for designing fast and robust algorithms. The features/representations are derived either from physicochemical properties or their structures in numerical form and are known as descriptors. In this work we develop two new molecular-fragment descriptors based on the critical analysis of existing descriptors. This development is primarily guided by the notion of coding degeneracy, and the ordering induced by the descriptor on the fragments. One of these descriptors is derived based on the simple graph representation of the molecule, and attempts to encode topological feature or the connectivity pattern in a hierarchical way without discriminating atom or bond types. Second descriptor extends the first one by weighing the atoms (vertices) in consideration with the bonding pattern, valence state and type of the atom. Further, the usefulness of these indices is tested by ranking and classifying molecules in two previously studied large heterogeneous data sets with regard to their anti-tubercular and other bacterial activity. This is achieved by developing a scoring function based on clustering using these new descriptors. Clusters are obtained by ordering the descriptors of training set molecules, and identifying the regions which are (almost) exclusively coming from active/inactive molecules. To test the activity of a new molecule, overlap of its descriptors in those cluster (interpolation) is weighted. Our results are found to be superior compared to previous studies: we obtained better classification performance by using only structural information while previous studies used both structural features and some physicochemical parameters. This makes our model simple, more interpretable and less vulnerable to statistical problems like chance correlation and over fitting. With focus on predictive modeling, we have carried out rigorous statistical validation. New descriptors utilize primarily the topological information in a hierarchical way. This can have significant implications in the design of new bioactive molecules (inverse QSAR, combinatorial library design) which is plagued by combinatorial explosion due to use of large number of descriptors. While the combinatorial generation of molecules with desirable properties is still a problem to be satisfactorily solved, our model has potential to reduce the number of degrees of freedom, thereby reducing the complexity.

La plupart des sites industriels abritent des équipements et des réservoirs sous pression. Pour des raisons diverses (suppression, impact mécanique, surchauffe ou autre), ils peuvent être endommagés et même éclater. Cette explosion peut engendrer de nombreux projectiles. Au cours de leur vol, ces derniers peuvent impacter d’autres équipements, tels que des réservoirs sous pression ou d’autres installations sensibles (poste de commande, par exemple). Si une des cibles impactées subit une ruine mécanique, elle peut exploser et générer une nouvelle série de projectiles. Ces projectiles menacent, à leur tour, d’autres installations et ainsi de suite. Ce type d’enchaînement accidentel catastrophique est connu sous le nom d’effet domino ou de suraccident. Dans ce document, l’effet domino pouvant se produire sur des sites industriels est analysé au travers des projections produites par l’accident initial. Une approche probabiliste globale est ainsi développée dans laquelle le calcul de la probabilité d’occurrence du phénomène requiert le passage par quatre étapes : - Analyse des termes sources : les projectiles générés par l’explosion d’un réservoir ont différentes caractéristiques, à savoir le nombre de projectiles, la forme, la masse, la vitesse de départ et les angles de départ. Toutes ces grandeurs sont modélisées par des variables aléatoires. A l’aide du principe du maximum d’entropie et des données existantes, des distributions probabilistes sont développées pour toutes ces variables. On se limite, cependant, au cas de l’explosion d’un réservoir cylindrique ou sphérique. – Analyse de l’impact ou analyse du mouvement : la trajectoire d’un projectile (ou fragment de structure), en fonction de ses caractéristiques de départ, est décrite par une combinaison des effets d’inertie, de gravitation et d’aérodynamique. Une approche simplifiée faisant l’hypothèse de constance des coefficients aérodynamiques permet d’identifier analytiquement la trajectoire du projectile tandis qu’une solution numérique est obtenue par une approche complète où toutes les valeurs de ces coefficients sont prises en compte.Les mouvements de translation et de rotation sont également étudiés. A l’aide de l’analyse complète et des conditions d’impact, la probabilité d’impact est déterminée. L’étude est restreinte à des projectiles en forme de fond de réservoir, fond oblong de réservoir et plaque. Les formes des cibles de l’étude sont restreintes au cas ellipsoïdal, cylindrique et cubique. – Analyse de l’état des cibles impactées : dans un premier temps, des modèles simplifiés d’impact sont utilisés afin d’étudier l’interaction mécanique entre les projectiles et les réservoirs impactés. Un modèle mécanique complet comprenant une loi de comportement élasto-plastique et un modèle de rupture est également proposé. Ce modèle est ensuite implémenté dans un code de calcul sans maillage de type SPH, i.e. Smoothed Particle Hydrodynamics. Afin d’estimer la probabilité de rupture des réservoirs impactés, les modèles simplifiés sont mis en œuvre, ce qui permet de réduire le coût de calcul. – Occurrence du sur-accident : selon l’état mécanique résiduel de la cible et son état physique (conditions thermodynamiques, niveau de remplissage, etc.), l’impact de projectiles peut conduire à la poursuite du pnénomène. Ce dernier point n’est pas traité dans le document présenté / Industrial facilities, such as vessels under pressure, might be damaged by explosions caused by an overpressure, an exterior mechanical impact or an overheating for instance. In general, such explosions generate many structural fragments. During their flight, these projectiles may impact other facilities, such as vessels under pressure, in the vicinity. Under given conditions of pressure and mechanical damage, these impacted targets may explode and generate other sets of structural fragments, and so on. This kind of scenario corresponds to the so-called domino effect. In this document, the domino effect caused by projections that may occur in the industrial sites is analyzed with a stochastic framework. For this purpose, a global methodology is developed. The determination of the occurrence probability of this effect requires four steps : - source terms analysis : the structural fragments generated by vessels explosions have different features, i.e. number of fragments, shape, mass, departure velocity and departure angles. These features are considered as random variables. Based on the maximum entropy principle and according to existing data, the probabilistic distributions are developed for each variable. This study focuses on the case of explosions in cylindrical or spherical vessels. – Fragments motion and impact analysis : according to the fragments features at their departure, the fragment trajectory is evaluated under the effects combined from the inertia, the gravitation and the aerodynamics. The simplified approach, under the hypothesis of constant aerodynamic coefficients, allows the analytical description of the trajectory whereas the numerical solutions are obtained for the complete approach when these coefficients vary. The translational as well as rotational movements are also considered. Monte Carlo simulations are performed in order to estimate the probability of impact. Three fragments shapes are considered : end-cap, oblong end-cap and plate. Three main shapes are investigated for the targets : ellipsoidal, cylindrical and cubic vessels. – Analysis of the mechanical behaviour of the impacted targets : simplified models are developed in order to study the mechanical interaction between the fragments and the impacted targets. A complete mechanical model, including elastic-plastic behaviour and a fissure model are also proposed. This model is then implemented in the mesh-free code (Smoothed Particles Hydrodynamics). In order to estimate the rupture probability of the impacted targets, the simplified models are used, reducing therefore the calculation duration. – Domino effect occurrence : according to its residual bearing capacity and its internal physical conditions, the impacted target may give rise to a new sequence of explosions and fragments generation. This last point is not studied in this document

Handschriften wurden schon seit dem Mittelalter häufig ausgemustert und recycelt. Daher existieren von vielen heute nur noch Bruchstücke. Das digitale Zeitalter, das die Handschrift in immer mehr Lebensbereichen zurückdrängt, hilft nun einem internationalen Netzwerk von Bibliotheken, diese alten Handschriftenreste wieder ans Licht zu bringen. Seit Mai 2016 beteiligt sich die UB Leipzig mit großzügiger Unterstützung der Alfried Krupp von Bohlen und Halbach-Stiftung an einem internationalen Projekt zum Aufbau einer Datenbank und virtuellen Arbeitsplattform für Handschriftenfragmente.

Monoclonal antibody MEM-57 recognizes CD3 antigen expressed on peripheral blood T-lymphocytes. CD3 surface glycoprotein complex associates with T-cell receptor and is responsible for the transduction of activation signal. Antibody MEM-57 has, therefore, a large diagnostic and therapeutic potential. It could be used in autoimmune diseases diagnostics, for classification of T-cell leukemias and, as an immunosuppressant, in transplantation. The most promising therapeutic use of MEM-57 antibody would be the construction of a "Bispecific T-cell Engager" (BiTE) antibody format with potential application in cancer therapy. In this format, single-chain variable fragment (scFv) of MEM-57 would be fused with an anti-tumor antigen scFv. The thesis is focused on biochemical and biophysical characterization of MEM-57 antibody scFv fragment. Recombinant antibody fragment scFv MEM-57, equipped with the pelB leader sequence, c-myc tag and His5 tag, was produced from a pET22b(+) vector into the periplasmic space of E. coli BL21 (DE3). Two-step purification protocol, employing nickel chelation affinity chromatography and ion-exchange chromatography, was developed to obtain high yield of pure protein. The antigen binding activity of scFv MEM-57 was confirmed by flow cytometry. Structural information on scFv MEM-57...

Fragment-screening by X-ray crystallography (XFS) is an expensive and low throughput fragment drug discovery screening method, and it requires a lot of optimization for each protein target. The advantages with this screening method are that it is very sensitive, it directly gives the three-dimensional structure of the protein-fragment complexes, and false positives are rarely obtained. The aim of this project was to help Sprint Bioscience assess if the advantages with XFS outweigh the disadvantages, and if this method should be used as a complement to their differential scanning fluorimetry (DSF) screening method. An XFS campaign was run using the oncoprotein vaccinia related kinase 1 (VRK1) as a target protein to evaluate this screening method. During the development of the XFS campaign, a diverse fragment library was created which consisted of 298 fragments that were all soluble in DMSO at 1 M concentration. The crystallization of the protein VRK1 was also optimized in this project to get a robust, high throughput crystallization set up which generated crystals that diffracted at higher resolution than 2.0 Å when they were not soaked with fragments. The soaking protocol was also optimized in order to reduce both the steps during the screening procedure and mechanical stress caused to the crystals during handling. Lastly, the created fragment library was used in screening VRK1 at 87.5 mM concentration with XFS. 23 fragment hits could be obtained from the X-ray crystallography screening campaign, and the mean resolution of the crystal structures of the protein-fragment complexes was 1.87Å. 11 of the 23 fragment hits were not identified as hits when they were screened against VRK1 using DSF. XFS was deemed as a suitable and efficient screening method to complement DSF since the hit rate was high and fragments hits could be obtained with this method that could not be obtained with DSF. However, in order to use this screening method a lot of time needs to be spent in optimizing the crystal system so it becomes suitable for fragment screening. Sprint Bioscience would therefore need to evaluate the cost/benefit ratio of using this screening method for each new project.

Background: We performed a biomechanical comparison of 2 methods for operative stabilization of pronation-abduction stage III ankle fractures; group 1: Anterior-posterior lag screws fixing the posterior tibial fragment and lateral fibula plating (LSLFP) versus group 2: locked plate fixation of the posterior tibial fragment and posterior antiglide plate fixation of the fibula (LPFP). Methods: Seven pairs of fresh-frozen osteoligamentous lower leg specimens (2 male, and 5 female donors) were used for the biomechanical testing. Bone mineral density (BMD) of each specimen was assessed by means of dual-energy x-ray absorptiometry. After open transection of the deltoid ligament, an osteotomy model of pronation abduction stage III ankle fracture was created. Specimens were systematically assigned to LSLFP (group 1, left ankles) or LPPFP (group 2, right ankles). After surgery, all specimens were evaluated via CT to verify reduction and fixation. Axial load was then applied onto each specimen using a servohydraulic testing machine starting from 0 N (Zwick/Roell, Ulm, Germany) at a speed of 10 N/s with the foot fixed in a 10 degrees pronation and 15 degrees dorsiflexion position. Construct stiffness, yield, and ultimate strength were measured and dislocation patterns were documented with a high-speed camera. The normal distribution of all data was analyzed using Shapiro-Wilk test. The group comparison was performed using paired Student t test. Statistical significance was assumed at a P value of .05. Results: All specimens had BMD values consistent with osteoporosis. BMD values did not differ between the left and right ankles of the same pair (P = .762). The mean BMD values between feet of men (0.603 g/cm²) and women (0.329 g/cm²) were statistically different (P = .005). The ultimate strength for LSLFP (group 1) with 1139 ± 669 N and LPPFP (group 2) with 2008 ± 943 N was statistically different (P = .036) as well as the yield in LSLFP (group 1) 812 ± 452 N and LPPFD (group 2) 1292 ± 625 N (P = .016). Construct stiffness trended to be higher in group 2 (179 ± 100 kNn) compared to group 1 (127 ± 73 kN/m) but this difference was not statistically significant (P = .120). BMD correlated with bone-construct failure. Conclusion: Fixation of the posterior tibial edge with a posterolateral locking plate resulted in higher biomechanical stability than anterior-posterior lag screw fixation in an osteoporotic pronation-abduction fracture model. Clinical Relevance: The clinical implication of this biomechanical study is that the posterior antiglide plating might be advantageous in patients with osteoporotic pronation abduction stage III ankle fracture.

Notre thèse explore les multiples voies proposées par Anne-Marie Albiach, Myung Mi Kim et Susan Howe pour organiser visuellement l’espace de la page. L’usage de la dimension visuelle en poésie ouvre des possibilités que le Verbe a toujours eues : dépeindre, se dédoubler, et produire un écho visuel et sonore. La dimension du voir permet également la création de paradoxes par des juxtapositions d’éléments. Tout cela met en question le statut du langage et du langage poétique. Cette thèse étudie les moyens par lesquels des poésies interpellent leurs lecteurs et continuent à produire des significations qui dépassent par leur multiplicité la formation traditionnelle du sens. Ces œuvres créent des significations que l’on doit voir, et non comprendre, par le biais d’une lecture plurielle de composants [iconographiques, linguistiques, abstraits, sériels]. On prend comme point de départ l’étude des typologies du fragment et illustre comment la discrétion visuelle du fragment est intimement liée au développement de chaque poète. On interroge le rapport du mot à l’image afin de dégager des antécédents des procédés utilisés sur la page. On confirme que ces œuvres emploient des techniques « iconiques », comme le faisaient les calligrammes d’Apollinaire, mais y associent les techniques mallarméennes en étendant la lecture sur plusieurs pages. Les poésies de Howe, d’Albiach et de Kim présentent une synesthésie totale des correspondances entre des formes jusqu’à-là exploitées séparément. Par conséquent, ces œuvres radicalisent la notion de possible poétique en assimilant les techniques de la publicité, de la pop culture, du collage et du montage. / This dissertation explores the diverse ways in which the work of Anne-Marie Albiach, Myung Mi Kim and Susan Howe visually organise the space of the page. The use of poetry’s visual dimension enlarges the traditional possibilities of the Word: to depict, multiply and produce an echo which is simultaneously resonant and visual. Exploiting the gaze also creates paradoxes through the juxtaposition of various elements. All of this calls into question the status of language, and poetic language in particular. This dissertation studies the ways these poets engage their readers as they produce a plurality of meanings which extend far beyond traditional sense-making. These works have significations which need to be seen rather than understood, via a reading process of its multifarious components [iconographic, linguistic, abstract, in series]. This study’s point of departure is the consideration of various types of fragments which illustrate how the fragment’s visual subtlety is intimately linked to each poet’s development. Connections between word and image are closely examined in order to locate the antecedents for the procedures being applied to the page. These works use “iconographic” techniques much as Apollinaire did in his calligrammes, while associating with these Mallarmé’s methods of drawing a poem’s reading out over numerous pages. The poetries of Howe, Albiach and Kim present a synesthesia of correspondences between all the forms which had heretofore been used separately. Consequently, these works radicalize the notion of what is possible in poetry by assimilating advertising, pop culture, collage and montage techniques.

Microcantilevers have been investigated as high sensitivity, label free biosensors for approximately 15 years. In nearly all cases, a thin gold film deposited on the microcantilevers is used as an intermediate attachment layer because of the convenience of thiol-gold chemistry. Unfortunately, this attachment chemistry can be unstable when used with complex sample media such as blood plasma. The Nordin group at BYU has recently developed an all-silicon in-plane photonic microcantilever (PMCL) technology to serve as a platform for label-free biosensing. It has the advantage of being readily scalable to simultaneous readout of many PMCLs in array format, and allows integration with polymer microfluidics to facilitate the introduction of biological samples and reagents. An essential processing step for the transformation of the PMCL into a practical biosensor is the ability to effectively immobilize active biological receptors directly on silicon PMCL surfaces such that ligand binding generates sufficient surface stress to cause measureable PMCL deflection. This dissertation presents the development of a method to functionalize the sensor surface of all-silicon in-plane photonic microcantilever (PMCL) arrays. This method employs a materials inkjet printer for non-contact jetting and a fluid that is custom designed for ink-jetting and biological applications with approximately 1 pL droplet size. The method facilitates the application of different receptors on select PMCLs with drop placement accuracy in the +/- 7.5 μm range. The functionalization fluid facilitates further processing using humidity control to achieve full coverage of only the PMCL's top surface and removal of dissolved salts to improve uniformity of receptor coverage and to prevent fouling of the sensor surface. Once a functionalization method was successfully developed, a series of experiments were performed to investigate the amount of surface stress that can be generated when receptors are immobilized directly to the silicon surface. In one series of experiments, a 4.8 μM streptavidin solution was used with biotin immobilized on multiple PMCLs to demonstrate adsorption-induced surface stress and concomitant deflection of the PMCL. The group observed ~ 15 nm PMCL deflection on average, with a corresponding surface stress of approximately 4 mN/m. These experiments yield the sensor response in real-time and employ a combination of multiple PMCLs functionalized as either sensors or unfunctionalized to serve as references. Investigation of various attachment chemistries is included, as well as a comparison with and without passivation of non-sensor surfaces. Investigated passivation strategies prevented ligand binding from generating a differential surface stress. Failure modes and physical mechanisms for adsorption-induced surface stress are discussed. Immobilization and passivation strategies for antibody-based biosensing are demonstrated with fluorescence microscopy and a corresponding PMCL sensing experiment using rabbit anti-goat F(ab') fragments as the receptors and Alex Fluor 488 labeled goat anti-rabbit IgGs as the ligand. While the results of these experiments remain inconclusive, suggestions for future research involving the PMCL sensor array are recommended.

Aus der Einleitung: 'Conceptual graphs (CGs) are an expressive formalism for representing knowledge about an application domain in a graphical way. Since CGs can express all of first-order predicate logic (FO), they can also be seen as a graphical notation for FO formulae. In knowledge representation, one is usually not only interested in representing knowledge, one also wants to reason about the represented knowledge. For CGs, one is, for example, interested in validity of a given graph, and in the question whether one graph subsumes another one. Because of the expressiveness of the CG formalism, these reasoning problems are undecidable for general CGs. In the literature [Sow84, Wer95, KS97] one can find complete calculi for validity of CGs, but implementations of these calculi have the same problems as theorem provers for FO: they may not terminate for formulae that are not valid, and they are very ineficient. To overcome this problem, one can either employ incomplete reasoners, or try to find decidable (or even tractable) fragments of the formalism. This paper investigates the second alternative. The most prominent decidable fragment of CGs is the class of simple conceptual graphs (SGs), which corresponds to the conjunctive, positive, and existential fragment of FO (i.e., existentially quantified conjunctions of atoms). Even for this simple fragment, however, subsumption is still an NP-complete problem [CM92]. SGs that are trees provide for a tractable fragment of SGs, i.e., a class of simple conceptual graphs for which subsumption can be decided in polynomial time [MC93]. In this report, we will identify a tractable fragment of SGs that is larger than the class of trees. Instead of trying to prove new decidability or tractability results for CGs from scratch, our idea was to transfer decidability results from description logics [DLNN97, DLNS96] to CGs. The goal was to obtain a \natural' sub-class of the class of all CGs in the sense that, on the one hand, this sub-class is defined directly by syntactic restrictions on the graphs, and not by conditions on the first-order formulae obtained by translating CGs into FO, and, on the other hand, is in some sense equivalent to a more or less expressive description logic. Although description logics (DLs) and CGs are employed in very similar applications (e.g., for representing the semantics of natural language sentences), it turned out that these two formalisms are quite different for several reasons: (1) conceptual graphs are interpreted as closed FO formulae, whereas DL concept descriptions are interpreted by formulae with one free variable; (2) DLs do not allow for relations of arity > 2 ; (3) SGs are interpreted by existential sentences, whereas almost all DLs considered in the literature allow for universal quantification; (4) because DLs use a variable-free syntax, certain identifications of variables expressed by cycles in SGs and by co-reference links in CGs cannot be expressed in DLs. As a consequence of these differences, we could not identify a natural fragment of CGs corresponding to an expressive DL whose decidability was already shown in the literature. We could, however, obtain a new tractability result for a DL corresponding to SGs that are trees. This correspondence result strictly extends the one in [CF98]. In addition, we have extended the tractability result from SGs that are trees to SGs that can be transformed into trees using a certain \cycle-cutting' operation. The report is structured as follows. We first introduce the description logic for which we will identify a subclass of equivalent SGs. In Section 3, we recall basic definitions and results on SGs. Thereafter, we introduce a syntactical variant of SGs which allows for directly encoding the support into the graphs (Section 4.1). In order to formalize the equivalence between DLs and SGs, we have to consider SGs with one distinguished node called root (Section 4.2). In Section 5, we finally identify a class of SGs corresponding to a DL that is a strict extension of the DL considered in [CF98].