Carbohydrate Conformation and Lipid Condensation in Monolayers Containing Glycosphingolipid Gb3: Influence of Acyl Chain Structure

AbstractGlobotriaosylceramide (Gb3), a glycosphingolipid found in the plasma membrane of animal cells, is the endocytic receptor of the bacterial Shiga toxin. Using x-ray reflectivity (XR) and grazing incidence x-ray diffraction (GIXD), lipid monolayers containing Gb3 were investigated at the air-water interface. XR probed Gb3 carbohydrate conformation normal to the interface, whereas GIXD precisely characterized Gb3’s influence on acyl chain in-plane packing and area per molecule (APM). Two phospholipids, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), were used to study Gb3 packing in different lipid environments. Furthermore, the impact on monolayer structure of a naturally extracted Gb3 mixture was compared to synthetic Gb3 species with uniquely defined acyl chain structures. XR results showed that lipid environment and Gb3 acyl chain structure impact carbohydrate conformation with greater solvent accessibility observed for smaller phospholipid headgroups and long Gb3 acyl chains. In general, GIXD showed that Gb3 condensed phospholipid packing resulting in smaller APM than predicted by ideal mixing. Gb3’s capacity to condense APM was larger for DSPC monolayers and exhibited different dependencies on acyl chain structure depending on the lipid environment. The interplay between Gb3-induced changes in lipid packing and the lipid environment’s impact on carbohydrate conformation has broad implications for glycosphingolipid macromolecule recognition and ligand binding

Detecting differential allelic expression using high-resolution melting curve analysis: application to the breast cancer susceptibility gene CHEK2

<p>Abstract</p> <p>Background</p> <p>The gene <it>CHEK2 </it>encodes a checkpoint kinase playing a key role in the DNA damage pathway. Though <it>CHEK2 </it>has been identified as an intermediate breast cancer susceptibility gene, only a small proportion of high-risk families have been explained by genetic variants located in its coding region. Alteration in gene expression regulation provides a potential mechanism for generating disease susceptibility. The detection of differential allelic expression (DAE) represents a sensitive assay to direct the search for a functional sequence variant within the transcriptional regulatory elements of a candidate gene. We aimed to assess whether <it>CHEK2 </it>was subject to DAE in lymphoblastoid cell lines (LCLs) from high-risk breast cancer patients for whom no mutation in <it>BRCA1</it> or <it>BRCA2</it> had been identified.</p> <p>Methods</p> <p>We implemented an assay based on high-resolution melting (HRM) curve analysis and developed an analysis tool for DAE assessment.</p> <p>Results</p> <p>We observed allelic expression imbalance in 4 of the 41 LCLs examined. All four were carriers of the truncating mutation 1100delC. We confirmed previous findings that this mutation induces non-sense mediated mRNA decay. In our series, we ruled out the possibility of a functional sequence variant located in the promoter region or in a regulatory element of <it>CHEK2 </it>that would lead to DAE in the transcriptional regulatory milieu of freely proliferating LCLs.</p> <p>Conclusions</p> <p>Our results support that HRM is a sensitive and accurate method for DAE assessment. This approach would be of great interest for high-throughput mutation screening projects aiming to identify genes carrying functional regulatory polymorphisms.</p

Etude de la dienophilie des benzofurannes et indoles. Application à la synthèse d analogues de la galanthamine

La réaction de Diels-Alder fait partie des moyens convergents pour assembler des hétérocycles de façon efficace et stéréosélective. Du fait de leur caractère aromatique riche en électrons, les benzofurannes et les indoles sont rarement utilisés en tant que diénophiles en réaction de cycloaddition [4+2] à demande électronique normale. Néanmoins, nous avons montré que, si les substrats benzofuranniques étaient correctement substitués par un groupement électroattracteur en position 3, la réaction conduit à un cycloadduit tricyclique désaromatisé portant un carbone quaternaire en jonction de cycle et une stéréochimie cis. Cet intermédiaire synthétique oxygéné présente un motif structural commun aux alcaloïdes d Opiacées et d Amaryllidacées, notamment la galanthamine utilisée actuellement dans le cadre du traitement de la maladie d Alzheimer. Dans le but de mettre au point cette méthodologie de synthèse, différentes substitutions du noyau aromatique et plusieurs méthodes d activation de la réaction de Diels-Alder, thermique, hyperbare et/ou acidocatalysées, ont été expérimentées. Le développement de cette méthodologie permet à présent d envisager la suite de la synthèse totale de la galanthamine. Son analogue azoté, l azagalanthamine, pourrait être accessible de manière analogue en utilisant une réaction de Diels-Alder à partir d indoles. Dans ce contexte, nous avons envisagé une réaction intramoléculaire et avons optimisé les substituants des parties diénique et diénophilique. Les cycloadduits tétracycliques cibles sont des analogues de la cétone de Büchi, intermédiaire-clé dans la synthèse d alcaloïdes de type Aspidosperma et Strychnos.The Diels-Alder approach is a very convergent way of assembling heterocycles rapidly and stereoselectively. Because of their aromaticity, the electron-rich benzofurans and indoles have not been used very often as dienophiles in normal electron demand [4+2] cycloaddition. We have shown that, when properly substituted by electron withdrawing group in position 3, benzofurans can lead to desaromatised tricyclic cycloadducts featuring a quaternary carbon at ring junction and a cis stereochemistry. These oxygenated skeletons possess a framework common to Opium and Amaryllidaceae alkaloids, galanthamine, used in Alzheimer s disease treatment, has been selected as a potential molecular target for the application of this approach. In order to develop this synthetic methodology, the influence of various substituents on the aromatic benzofuran ring was studied as well as the activation mode, thermal, hyperbaric and/or by Lewis acid. The cycloaddition reaction was optimized and the results gathered so far allow to envision total synthesis of galanthamine. The possibility of reaching the nitrogenated analogue azagalanthamine throught a similar approach using indoles was also considered. An intramolecular cycloaddition was envisaged and optimization of the synthesis of several substrates was carried out. The target tetracyclic adducts are similar to Büchi s ketone, a key intermediate in the preparation Aspidosperma and Strychnos alkaloids.ROUEN-BU Sciences (764512102) / SudocSudocFranceF

Synthesis of the Azetidinyl-Thiazoline Fragment of Vioprolides A and C

An efficient synthesis of the azetidinyl-thiazoline fragment of the antifungal and cytotoxic macrolides vioprolides A and C is reported. Key steps of the ynthesis include formation of the thiazoline by condensation of N-Alloc-trans (2S,4R)-4-methylazetidine-2-carbonitrile with L-cysteine and formation of the four-membered ring by intramolecular alkylation of a suitably protected N-Alloc derivative prepared from (R)-alaninol.info:eu-repo/semantics/publishe

Design Polysaccharides of Marine Origin: Chemical Modifications to Reach Advanced Versatile Compounds

Polysaccharides are among the most abundant macromolecules on Earth. These polymers are easily obtained from various marine resources such as algae, microorganisms and crustacean shells. The structure of these natural carbohydrates is innovative and quite complex. Marine biopolymers represent key scaffolds toward large challenging fields, such as biomedical applications (glycosaminoglycans, regenerative medicine and drug delivery) and tailored biomaterials. Chemical modifications can be applied to modify their final properties in a specific purpose. New functional glycans are achievable and represent a real potential with their intrinsic biocompatibility and biodegradability. Hydroxyl groups are ubiquitous in polysaccharides structure and involved in most of the chemical modifications. The most useful functionalities are ester, ether, amide, amine and alkyl groups. The starting materials could be a natural or depolymerized polymers and the reaction considered with a regioselective point of view. In this review, we will focus on chitin polysaccharide, which is extracted according to industrial processing from exoskeleton of several marine crustaceans. A subsequent deacylation provides chitosan. This marine polysaccharide is very similar to cellulose, a widespread fiber plant organic polymer, except for an amine group on the C2 position instead of a hydroxyl group. Furthermore, seaweeds provide the most abundant sources of polysaccharides: alginates, agar/agarose, carrageenans and fuco dans. In order to improve the original physicochemical and biochemical properties, we will highlight the chemical modifications involving the listed marine polysaccharides of interest

Enigmatic occurrence of NDM-7 enzyme in the community

International audienceA 79-year-old French woman living in a nursing home was brought to the hospital emergency room for indwelling urinary catheter re-insertion following accidental removal. Despite no clinical signs suggesting infection, urine was sent to the laboratory for microbiological and cytological analysis. An Escherichia coli bacteriuria (104 CFU/mL) was found, but no leukocyturia. Antibiotic susceptibility testing revealed an isolate with resistance to penicillins, cephalosporins, aztreonam, ertapenem, nalidixic acid, fluoroquinolones, tetracycline, aminoglycosides, trimethoprim/sulfonamides and temocillin

Carbohydrate Conformation and Lipid Condensation in Monolayers Containing Glycosphingolipid Gb3: Influence of Acyl Chain Structure

Globotriaosylceramide (Gb3), a glycosphingolipid found in the plasma membrane of animal cells, is the endocytic receptor of the bacterial Shiga toxin. Using x-ray reflectivity (XR) and grazing incidence x-ray diffraction (GIXD), lipid monolayers containing Gb3 were investigated at the air-water interface. XR probed Gb3 carbohydrate conformation normal to the interface, whereas GIXD precisely characterized Gb3’s influence on acyl chain in-plane packing and area per molecule (APM). Two phospholipids, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), were used to study Gb3 packing in different lipid environments. Furthermore, the impact on monolayer structure of a naturally extracted Gb3 mixture was compared to synthetic Gb3 species with uniquely defined acyl chain structures. XR results showed that lipid environment and Gb3 acyl chain structure impact carbohydrate conformation with greater solvent accessibility observed for smaller phospholipid headgroups and long Gb3 acyl chains. In general, GIXD showed that Gb3 condensed phospholipid packing resulting in smaller APM than predicted by ideal mixing. Gb3’s capacity to condense APM was larger for DSPC monolayers and exhibited different dependencies on acyl chain structure depending on the lipid environment. The interplay between Gb3-induced changes in lipid packing and the lipid environment’s impact on carbohydrate conformation has broad implications for glycosphingolipid macromolecule recognition and ligand binding

SMAD6 overexpression leads to accelerated myogenic differentiation of LMNA mutated cells

Abstract LMNA gene encodes lamins A and C, two major components of the nuclear lamina, a network of intermediate filaments underlying the inner nuclear membrane. Most of LMNA mutations are associated with cardiac and/or skeletal muscles defects. Muscle laminopathies include Emery-Dreifuss Muscular Dystrophy, Limb-Girdle Muscular Dystrophy 1B, LMNA-related Congenital Muscular Dystrophy and Dilated Cardiomyopathy with conduction defects. To identify potential alterations in signaling pathways regulating muscle differentiation in LMNA-mutated myoblasts, we used a previously described model of conditionally immortalized murine myoblasts: H-2K cell lines. Comparing gene expression profiles in wild-type and Lmna ∆8–11 H-2K myoblasts, we identified two major alterations in the BMP (Bone Morphogenetic Protein) pathway: Bmp4 downregulation and Smad6 overexpression. We demonstrated that these impairments lead to Lmna ∆8–11 myoblasts premature differentiation and can be rescued by downregulating Smad6 expression. Finally, we showed that BMP4 pathway defects are also present in myoblasts from human patients carrying different heterozygous LMNA mutations