Design and optimization of selective serotonin re-uptake inhibitors with high synthetic accessibility Part 1

The reported selective serotonin Re-uptake Inhibitor Litoxetine was used as the starting point in the design of a range of potential SSRIs with high ease of synthetic accessibility. Preparation and subsequent optimization yielded a range of potent and highly selective SSRIs.     

Crumbs Affects Protein Dynamics In Anterior Regions Of The Developing Drosophila Embryo

Maintenance of apico-basal polarity is essential for epithelial integrity and requires particular reinforcement during tissue morphogenesis, when cells are reorganised, undergo shape changes and remodel their junctions. It is well established that epithelial integrity during morphogenetic processes depends on the dynamic exchange of adherens junction components, but our knowledge on the dynamics of other proteins and their dynamics during these processes is still limited. The early Drosophila embryo is an ideal system to study membrane dynamics during morphogenesis. Here, morphogenetic activities differ along the anterior-posterior axis, with the extending germband showing a high degree of epithelial remodelling. We developed a Fluorescence Recovery After Photobleaching (FRAP) assay with a higher temporal resolution, which allowed the distinction between a fast and a slow component of recovery of membrane proteins during the germband extension stage. We show for the first time that the recovery kinetics of a general membrane marker, SpiderGFP, differs in the anterior and posterior parts of the embryo, which correlates well with the different morphogenetic activities of the respective embryonic regions. Interestingly, absence of crumbs, a polarity regulator essential for epithelial integrity in the Drosophila embryo, decreases the fast component of SpiderGFP and of the apical marker Stranded at Second-Venus specifically in the anterior region. We suggest that the defects in kinetics observed in crumbs mutant embryos are the first signs of tissue instability in this region, explaining the earlier breakdown of the head epidermis in comparison to that of the trunk, and that diffusion in the plasma membrane is affected by the absence of Crumbs.     

Tryptophan 110, a residue involved in the toxic activity but not in the enzymatic activity of notexin

We prepared two derivatives of notexin, a phospholipase A2 from Notechis scutatus scutatus venom, by modifying the protein with 2-nitrophenylsulfenylchloride, a tryptophan-specific reagent. One derivative was modified at both tryptophans 20 and 110 whereas the other was modified at tryptophan 20. Evidence based on circular dichroic analysis and antigenicity towards a notexin-specific monoclonal antibody indicated that derivatization at both tryptophans did not affect the tertiary structure of notexin. Concomitant modification of tryptophans 20 and 110 induced a marked decrease in the capacity of notexin to kill mice and to block neuromuscular transmission in the chick biventer cervicis preparation, whereas selective modification at tryptophan 20 had no effect on the lethal properties of notexin. This implies that the decrease in the lethal properties of notexin after derivatization was due to modification at tryptophan 110. However, the diderivatized notexin retained full enzymatic activity, implying that neither tryptophan 20 and tryptophan 110 are involved in the catalytic function of the molecule. We conclude that notexin harbours two functional sites. One of them corresponds to the enzymatic site, whereas the other, which includes tryptophan 110, provides specific toxic characteristics to notexin. By reference to previous crystallographic studies, the relative spatial positions of elements involved in toxicity and the catalytic site, we propose a possible orientation of notexin with respect to its putative membrane-bound target.     

A Novel Optical Intracellular Imaging Approach for Potassium Dynamics in Astrocytes

Astrocytes fulfill a central role in regulating K⁺ and glutamate, both released by neurons into the extracellular space during activity. Glial glutamate uptake is a secondary active process that involves the influx of three Na⁺ ions and one proton and the efflux of one K⁺ ion. Thus, intracellular K⁺ concentration ([K⁺]_i) is potentially influenced both by extracellular K⁺ concentration ([K⁺]_o) fluctuations and glutamate transport in astrocytes. We evaluated the impact of these K⁺ ion movements on [K⁺]_i in primary mouse astrocytes by microspectrofluorimetry. We established a new noninvasive and reliable approach to monitor and quantify [K⁺]_i using the recently developed K⁺ sensitive fluorescent indicator Asante Potassium Green-1 (APG-1). An in situ calibration procedure enabled us to estimate the resting [K⁺]_i at 133±1 mM. We first investigated the dependency of [K⁺]_i levels on [K⁺]_o. We found that [K⁺]_i followed [K⁺]_o changes nearly proportionally in the range 3–10 mM, which is consistent with previously reported microelectrode measurements of intracellular K⁺ concentration changes in astrocytes. We then found that glutamate superfusion caused a reversible drop of [K⁺]_i that depended on the glutamate concentration with an apparent EC₅₀ of 11.1±1.4 µM, corresponding to the affinity of astrocyte glutamate transporters. The amplitude of the [K⁺]_i drop was found to be 2.3±0.1 mM for 200 µM glutamate applications. Overall, this study shows that the fluorescent K⁺ indicator APG-1 is a powerful new tool for addressing important questions regarding fine [K⁺]_i regulation with excellent spatial resolution.     

Recombinant human IL-6 expressed inE. coli undergoes selective N-terminal degradation: Evidence that the protein consists of a stable core and a nonessential flexible N-terminal

A synthetic gene for human interleukin-6 has been expressed inE. coli. The protein has been purified and renatured and has the same activity as natural human IL-6 using the 7TD1 cell proliferation assay. The protein undergoes specific cleavage by a thiol protease, yielding two new N-termini at Arg-9 and His-15. The truncated proteins retain full biological activity. The degradation results in the loss of sharp amide resonances in the¹H-NMR spectrum, and little change to the ultraviolet CD spectrum. Several amino acid type assignments could be made for these sharp amides using a DQF-COSY 2D-NMR experiment. The N-terminal 15 amino acids exist as a flexible, random coil, attached to a central structure.     

Spinning of hydroalcoholic chitosan solutions

We investigated the spinning of hydroalcoholic chitosan solutions. The dope composition was optimized in order to obtain a continuous alcogel fiber by water evaporation on heating the extruded hydroalcoholic solution. This alcogel fiber was then neutralized in aqueous alkali baths and washed in water to eliminate the residual alcohol and salts before final drying. Depending on the alcohol content in the filament at the neutralization step, on specific alcohol–chitosan interactions and on the nature and concentration of the coagulation base, the process yielded semicrystalline chitosan fibers with different proportions of anhydrous and hydrated allomorphs. Contrarily to the classical annealing method, the formation of mainly anhydrous crystals was obtained without significant molecular weight decrease by neutralizing the polymer in hydrophobic conditions. The control of allomorph content was shown to be related to the hydrophobicity of the solvent (alcohol fraction) at the neutralization step.