Colorimetric microtiter plate receptor-binding assay for the detection of freshwater and marine neurotoxins targeting the nicotinic acetylcholine receptors.

Anatoxin-a and homoanatoxin-a, produced by cyanobacteria, are agonists of nicotinic acetylcholine receptors (nAChRs). Pinnatoxins, spirolides, and gymnodimines, produced by dinoflagellates, are antagonists of nAChRs. In this study we describe the development and validation of a competitive colorimetric, high throughput functional assay based on the mechanism of action of freshwater and marine toxins against nAChRs.

Evaluation of fast 2D NMR for metabolomics.

Two-dimensional nuclear magnetic resonance (2D NMR) is increasingly explored as a tool for metabolomics because of its superior resolution compared to one-dimensional NMR (1D NMR). However, 2D NMR is characterized by longer acquisition times, which makes it less suitable for high-throughput studies. In this Article, we evaluated two methods for the acceleration of nD NMR, ultrafast (UF) and nonuniform sampling (NUS), in the context of metabolomics.

Coupling the Torpedo microplate-receptor binding assay with mass spectrometry to detect cyclic imine neurotoxins.

Cyclic imine neurotoxins constitute an emergent family of neurotoxins of dinoflagellate origin that are potent antagonists of nicotinic acetylcholine receptors. We developed a target-directed functional method based on the mechanism of action of competitive agonists/antagonists of nicotinic acetylcholine receptors for the detection of marine cyclic imine neurotoxins. The key step for method development was the immobilization of Torpedo electrocyte membranes rich in nicotinic acetylcholine receptors on the surface of microplate wells and the use of biotinylated-α-bungarotoxin as tracer.

Actin dynamics associated with focal adhesions.

Cell-matrix adhesion plays a major role during cell migration. Proteins from adhesion structures connect the extracellular matrix to the actin cytoskeleton, allowing the growing actin network to push the plasma membrane and the contractile cables (stress fibers) to pull the cell body. Force transmission to the extracellular matrix depends on several parameters including the regulation of actin dynamics in adhesion structures, the contractility of stress fibers, and the mechanosensitive response of adhesion structures.

SAXS and X-ray crystallography suggest an unfolding model for the GDP/GTP conformational switch of the small GTPase Arf6.

The small GTPases Arf1 and Arf6 have nonoverlapping functions in cellular traffic despite their very high sequence and structural resemblance. Notably, the exquisite isoform specificity of their guanine nucleotide exchange factors and their distinctive sensitivity to the drug brefeldin A cannot be explained by any straightforward structural model. Here we integrated structural and spectroscopic methods to address this issue using Δ13Arf6-GDP, a truncated mutant that mimics membrane-bound Arf6-GDP.

Ligand-binding assays for cyanobacterial neurotoxins targeting cholinergic receptors.

Toxic cyanobacterial blooms are a threat to public health because of the capacity of some cyanobacterial species to produce potent hepatotoxins and neurotoxins. Cyanobacterial neurotoxins are involved in the rapid death of wild and domestic animals by targeting voltage gated sodium channels and cholinergic synapses, including the neuromuscular junction. Anatoxin-a and its methylene homologue homoanatoxin-a are potent agonists of nicotinic acetylcholine receptors.

Total synthesis of (-)-exiguolide.

The first total synthesis of the naturally occurring enantiomer of exiguolide ((-)-1) has been completed. This very convergent synthesis features the following as main steps: (i) a Trost's ruthenium-catalyzed ene-yne cross-coupling reaction (this complex transformation allows the challenging control of the C5-C28 double bond geometry along with the stereoselective construction of the tetrahydropyran ring A) and (ii) a very efficient one-pot, two-step stereoselective conjugated allylic alcohol substitution that allowed the control of the C15 stereogenic center.

Guidelines for the use of band-selective radiofrequency pulses in hetero-nuclear NMR: example of longitudinal-relaxation-enhanced BEST-type 1H-15N correlation experiments.

Band-selective radiofrequency (rf) pulses provide powerful spectroscopic tools for many biomolecular NMR applications. Band-selectivity is commonly achieved by pulse shaping where the rf amplitude and phase are modulated according to a numerically optimized function. This results in complex spin evolution trajectories during the pulse duration.

Total synthesis of the antiproliferative macrolide (+)-neopeltolide.

A concise total synthesis of the very promising antiproliferative macrolide (+)-neopeltolide (1) has been performed in 16 steps. The main steps of this approach are a Ru(II)-catalyzed alkyne-enal coupling, a Pd0-catalyzed desulfurative cross-coupling, and a stereoselective In(III)-catalyzed propargylation. Four stereogenic centers out of six have been set thanks to substrate-controlled diastereoselective reactions with minimal reliance on protecting groups.

Probing the relationship between Gram-negative and Gram-positive S1 proteins by sequence analysis.

Escherichia coli ribosomal protein S1 is required for the translation initiation of messenger RNAs, in particular when their Shine-Dalgarno sequence is degenerated. Closely related forms of the protein, composed of the same number of domains (six), are found in all Gram-negative bacteria. More distant proteins, generally formed of fewer domains, have been identified, by sequence similarities, in Gram-positive bacteria and are also termed 'S1 proteins'.

One-pot syntheses of dissymmetric diamides based on the chemistry of cyclic monothioanhydrides. Scope and limitations and application to the synthesis of glycodipeptides.

Opening cyclic monothioanhydrides by amines provides a convenient entry into amido thioacids that can be trapped in situ by 2,4-dinitrobenzenesulfonamides, by electron-deficient azides, or by amines in the presence of Sanger's reagent leading, in each case, to dissymmetric diamides in what can be considered a one-pot, three-component coupling sequence. The use of monothiomaleic anhydride and bifunctional nucleophiles such as amino thiols provides access to heterocyclic amides. The low reactivity of cyclic monothioanhydrides toward alcohols enables the use of methanol as solvent and obviates the need for the protection of alcohols in the various reaction components.