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Peptide alkyl thioesters are versatile reagents in various synthetic applications, commonly generated from peptide hydrazides and thiols. However, a notable limitation is the need for a substantial excess of the thiol reagent, restricting the usage to simple thiols. Here, we introduce an adapted procedure that significantly enhances thioester production with just a minimal thiol excess, facilitating the use of advanced thiol nucleophiles.

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Methods enabling the dechalcogenation of thiols or selenols have been investigated and developed for a long time in fields of research as diverse as the study of prebiotic chemistry, the engineering of fuel processing techniques, the study of biomolecule structures and function or the chemical synthesis of biomolecules. The dechalcogenation of thiol or selenol amino acids is nowadays a particularly flourishing area of research for being a pillar of modern chemical protein synthesis, when used in combination with thiol or selenol-based chemoselective peptide ligation chemistries. This review offers a comprehensive and scholarly overview of the field, emphasizing emerging trends and providing a detailed and critical mechanistic discussion of the dechalcogenation methods developed so far. Taking advantage of recently published reports, it also clarifies some unexpected desulfurization reactions that were observed in the past and for which no explanation was provided at the time. Additionally, the review includes a discussion on principal desulfurization methods within the framework of newly introduced green chemistry metrics and toolkits, providing a well-rounded exploration of the subject.

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Macrostomum lignano, a marine free-living flatworm, has emerged as a potent invertebrate model in developmental biology for studying stem cells, germline, and regeneration processes. In recent years, many tools have been developed to manipulate this worm and to facilitate genetic modification. RNA interference is currently the most accessible and direct technique to investigate gene functions. It is obtained by soaking worms in artificial seawater containing dsRNA targeting the gene of interest. Although easy to perform, the original protocol calls for daily exchange of dsRNA solutions, usually until phenotypes are observed, which is both time- and cost-consuming. In this work, we have evaluated alternative dsRNA delivery techniques, such as electroporation and osmotic shock, to facilitate the experiments with improved time and cost efficiency. During our investigation to optimize RNAi, we demonstrated that, in the absence of diatoms, regular single soaking in artificial seawater containing dsRNA directly produced in bacteria or synthesized in vitro is, in most cases, sufficient to induce a potent gene knockdown for several days with a single soaking step. Therefore, this new and highly simplified method allows a very significant reduction of dsRNA consumption and lab work. In addition, it enables performing experiments on a larger number of worms at minimal cost.

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Providing biomolecules with extended physicochemical, biochemical, or biological properties is a contemporary challenge motivated by impactful benefits in life or materials sciences. In this study, we show that a latent and highly reactive oxalyl thioester precursor can be efficiently introduced as a pending functionality into a fully synthetic protein domain following a protection/late-stage deprotection strategy and can serve as an on-demand reactive handle. The approach is illustrated with the production of a 10 kDa ubiquitin Lys48 conjugate.

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4-Mercaptophenylacetic acid (MPAA) is a popular catalyst of the native chemical ligation (NCL) but has to be used in large excess for achieving practically useful rates (up to 50-100 equiv). We report here that the catalytic potency of MPAA can be boosted by introducing a stretch of arginines in the departing thiol from the thioester. By doing so, the electrostatically assisted NCL reaction proceeds rapidly by using substoichiometric concentrations of MPAA, an advantage that enables useful synthetic applications.

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Rodents are the most numerous order of mammals. The literature presents information on the arterial circle of the brain in capybara, the guinea pig of the family Caviidae and many other not so closely related rodent species. Information on the blood supply to the brain is often incomplete and focuses on one pathway in a broader comparative aspect. The supply of oxygen and nutrients to the brain is very important for its proper functioning. The aim of this study is to describe the pathways supplying blood to the cranial cavity and to describe the arterial circle of the brain in the Patagonian mara. The study was conducted on 46 specimens using two methods. The first of them used a stained solution of the chemo-setting acrylic material. The second one, the colored liquid LBS 3060 latex. The arterial circle of the brain is a heart-shaped structure. It is formed by rostral cerebral arteries, caudal communicating arteries and the basilar artery. Blood supplies the arterial circle of the brain in three ways. First one is the basilar artery, which originates from the vertebral arteries. The second one is the internal carotid artery which joins a branch from the external ophthalmic artery. The third is the internal ophthalmic artery, which branches from the external ophthalmic artery.

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One pillar of protein chemical synthesis based on the application of ligation chemistries to cysteine is the group of reactions enabling the selective desulfurization of cysteine residues into alanines. Modern desulfurization reactions use a phosphine as a sink for sulfur under activation conditions involving the generation of sulfur-centered radicals. Here we show that cysteine desulfurization by a phosphine can be effected efficiently by micromolar concentrations of iron under aerobic conditions in hydrogen carbonate buffer, that is using conditions that are reminiscent of iron-catalyzed oxidation phenomena occurring in natural waters. Therefore, our work shows that chemical processes taking place in aquatic systems can be adapted to a chemical reactor for triggering a complex chemoselective transformation at the protein level, while minimizing the resort to harmful chemicals.

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Antimicrobial peptides (AMPs) play a key role in the external immunity of animals, offering an interesting model for studying the influence of the environment on the diversification and evolution of immune effectors. Alvinellacin (ALV), arenicin (ARE) and polaricin (POL, a novel AMP identified here), characterized from three marine worms inhabiting contrasted habitats ('hot' vents, temperate and polar respectively), possess a well conserved BRICHOS domain in their precursor molecule despite a profound amino acid and structural diversification of the C-terminal part containing the core peptide. Data not only showed that ARE, ALV and POL display an optimal bactericidal activity against the bacteria typical of the habitat where each worm species lives but also that this killing efficacy is optimal under the thermochemical conditions encountered by their producers in their environment. Moreover, the correlation between species habitat and the cysteine contents of POL, ARE and ALV led us to investigate the importance of disulfide bridges in their biological efficacy as a function of abiotic pressures (pH and temperature). The construction of variants using non-proteinogenic residues instead of cysteines (α-aminobutyric acid variants) leading to AMPs devoid of disulfide bridges, provided evidence that the disulfide pattern of the three AMPs allows for a better bactericidal activity and suggests an adaptive way to sustain the fluctuations of the worm's environment. This work shows that the external immune effectors exemplified here by BRICHOS AMPs are evolving under strong diversifying environmental pressures to be structurally shaped and more efficient/specific under the ecological niche of their producer.

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The Balkan Peninsula region has a very diverse agricultural and livestock tradition, and almost every country has its own local breed of sheep. Different breeds of sheep and different breeding traditions, despite the small geographical distance, determine the morphological and morphometric variability among animal breeds. In this study, this morphological diversity among the skulls of sheep breeds of some countries in the Balkan region was examined by the geometric morphometric method. 2D images of 86 sheep skulls from five different countries were analyzed from the dorsal view.Sixteen landmarks were used. The Bardhoka and the Ivesi breed have the broadest distributions of skull shape amongst the sheep breeds. The Ruda sheep is the most morphologically conservative. The sheep from Turkey (Ivesi) and Kosovo (Bardhoka) seem to differ mainly from sheep from other Balkan countries. Bardhoka and Ruda differ most from each other (p < 0.0001). The next biggest differences were between Ivesi and Ruda (p < 0.0011) and between Bardhoka and Sharri sheep (p < 0.0016). The sheep breeds Dubska and Lara e Polisit differ the least from each other. Geometrics morphometric analysis is a useful tool to detect differences in the shape of the skull of different sheep breeds and can therefore be used successfully for taxonomic purposes.

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The discovery of novel antihelmintic molecules to combat the development and spread of schistosomiasis, a disease caused by several Schistosoma flatworm species, mobilizes significant research efforts worldwide. With a limited number of biochemical assays for measuring the viability of adult worms, the antischistosomicidal activity of molecules is usually evaluated by a microscopic observation of worm mobility and/or integrity upon drug exposure. Even if these phenotypical assays enable multiple parameters analysis, they are often conducted during several days and need to be associated with image-based analysis to minimized subjectivity. We describe here a self-purifying microfluidic system enabling the selection of healthy adult worms and the identification of molecules acting instantly on the parasite. The worms are assayed in a dynamic environment that eliminates unhealthy worms that cannot attach firmly to the chip walls prior to being exposed to the drug. The detachment of the worms is also used as second step readout for identifying active compounds. We have validated this new fluidic screening approach using the two major antihelmintic drugs, praziquantel and artemisinin. The reported dynamic system is simple to produce and to parallelize. Importantly, it enables a quick and sensitive detection of antischistosomal compounds in no more than one hour.

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The modification of protein electrostatics by phosphorylation is a mechanism used by cells to promote the association of proteins with other biomolecules. In this work, we show that introducing negatively charged phosphoserines in a reactant is a powerful means for directing and accelerating the chemical modification of proteins equipped with oppositely charged arginines. While the extra charged amino acid residues induce no detectable affinity between the reactants, they bring site-selectivity to a reaction that is otherwise devoid of such a property. They also enable rate accelerations of four orders of magnitude in some cases, thereby permitting chemical processes to proceed at the protein level in the low micromolar range, using reactions that are normally too slow to be useful in such dilute conditions.

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Hepatocyte growth factor (HGF) is the natural ligand of the MET receptor tyrosine kinase. This ligand-receptor couple is essential for the maturation process of hepatocytes. Previously, the rational design of a synthetic protein based on the assembly of two K1 domains from HGF led to the production of a potent and stable MET receptor agonist. In this study, we compared the effects of K1K1 with HGF during the differentiation of hepatocyte progenitors derived from human induced pluripotent stem cells (hiPSCs). In vitro, K1K1, in the range of 20 to 200 nM, successfully substituted for HGF and efficiently activated ERK downstream signaling. Analysis of the levels of hepatocyte markers showed typical liver mRNA and protein expression (HNF4α, albumin, alpha-fetoprotein, CYP3A4) and phenotypes. Although full maturation was not achieved, the results suggest that K1K1 is an attractive candidate MET agonist suitable for replacing complex and expensive HGF treatments to induce hepatic differentiation of hiPSCs.

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The last two decades have witnessed the rise in power of chemical protein synthesis to the point where it now constitutes an established corpus of synthetic methods efficiently complementing biological approaches. One factor explaining this spectacular evolution is the emergence of a new class of chemoselective reactions enabling the formation of native peptide bonds between two unprotected peptidic segments, also known as native ligation reactions. In recent years, their application has fueled the production of homogeneous batches of large and highly decorated protein targets with a control of their composition at the atomic level. In doing so, native ligation reactions have provided the means for successful applications in chemical biology, medicinal chemistry, materials science, and nanotechnology research.The native chemical ligation (NCL) reaction has had a major impact on the field by enabling the chemoselective formation of a native peptide bond between a C-terminal peptidyl thioester and an N-terminal cysteinyl peptide. Since its introduction in 1994, the NCL reaction has been made the object of significant improvements and its scope and limitations have been thoroughly investigated. Furthermore, the diversification of peptide segment assembly strategies has been essential to access proteins of increasing complexity and has had to overcome the challenge of controlling the reactivity of ligation partners.One hallmark of NCL is its dependency on thiol reactivity, including for its catalysis. While Nature constantly plays with the redox properties of biological thiols for the regulation of numerous biochemical pathways, such a control of reactivity is challenging to achieve in synthetic organic chemistry and, in particular, for those methods used for assembling peptide segments by chemical ligation. This Account covers the studies conducted by our group in this area. A leading theme of our research has been the conception of controllable acyl donors and cysteine surrogates that place the chemoselective formation of amide bonds by NCL-like reactions under the control of dichalcogenide-based redox systems. The dependency of the redox potential of dichalcogenide bonds on the nature of the chalcogenides involved (S, Se) has appeared as a powerful means for diversifying the systems, while allowing their sequential activation for protein synthesis. Such a control of reactivity mediated by the addition of harmless redox additives has greatly facilitated the modular and efficient preparation of multiple targets of biological relevance. Taken together, these endeavors provide a practical and robust set of methods to address synthetic challenges in chemical protein synthesis.

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Hepatocyte growth factor/scatter factor (HGF/SF) and its cognate receptor MET play several essential roles in embryogenesis and regeneration in postnatal life of epithelial organs such as the liver, kidney, lung, and pancreas, prompting a strong interest in harnessing HGF/SF-MET signalling for regeneration of epithelial organs after acute or chronic damage. The limited stability and tissue diffusion of native HGF/SF, however, which reflect the tightly controlled, local mechanism of action of the morphogen, have led to a major search of HGF/SF mimics for therapy. In this work, we describe the rational design, production, and characterization of K1K1, a novel minimal MET agonist consisting of two copies of the kringle 1 domain of HGF/SF in tandem orientation. K1K1 is highly stable and displays biological activities equivalent or superior to native HGF/SF in a variety of in vitro assay systems and in a mouse model of liver disease. These data suggest that this engineered ligand may find wide applications in acute and chronic diseases of the liver and other epithelial organs dependent of MET activation.

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N-selenoethyl cysteine (SetCys) in the form of its cyclic selenosulfide is a cysteine surrogate, whose reactivity depends on the reducing power of the medium. SetCys does not interfere with the native chemical ligation reaction under mild reducing conditions, that is in the absence of tris(2-carboxyethyl)phosphine (TCEP). In contrast, subjecting SetCys to TCEP results in the spontaneous loss of its N-selenoethyl appendage and thus to its conversion into a Cys residue. Therefore, SetCys can be used for the redox-controlled assembly of peptide segments using NCL. We provide in this protocol detailed procedures for the synthesis of Fmoc-protected SetCys residue and for its incorporation into peptides using standard solid-phase peptide synthesis protocols. We also describe its use for the chemical synthesis of proteins through the redox-controlled assembly of three peptide segments in one-pot.

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The arylthiol 4-mercaptophenylacetic acid (MPAA) is a powerful catalyst of selenosulfide bond reduction by the triarylphosphine 3,3',3″-phosphanetriyltris(benzenesulfonic acid) trisodium salt (TPPTS). Both reagents are water-soluble at neutral pH and are particularly adapted for working with unprotected peptidic substrates. Contrary to trialkylphosphines such as tris(2-carboxyethyl)phosphine hydrochloride (TCEP), TPPTS has the advantage of not inducing deselenization reactions. We believe that the work reported here will be of value for those manipulating selenosulfide bonds in peptidic or protein molecules.

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We show that latent oxalyl thioester surrogates are a powerful means to modify peptides and proteins in highly dilute conditions in purified aqueous media or in mixtures as complex as cell lysates. Designed to be shelf-stable reagents, they can be activated on demand to enable ligation reactions with peptide concentrations as low as a few hundred nM at rates approaching 30 M-1 s-1 .

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The native chemical ligation reaction of peptide thioesters with cysteinyl peptides is a pivotal chemical process in the production of native or modified peptides and proteins, and well beyond in the preparation of various biomolecule analogs and materials. To benefit from this reaction at its fullest and to access all the possible applications, the experimentalist needs to know the factors affecting its rate and how to control it. This concept article presents the fundamental principles underlying the rate of the native chemical ligation and its homogeneous catalysis by nucleophiles. It has been prepared to serve as a quick guide in the search for an appropriate catalyst.

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The analyses were performed on a right third premolar (P3) of a white rhinoceros female (Ceratotherium simum, Burchell 1817). The specimen was born in captivity at London Zoo (Zoological Society of London), then in the 1970s transferred to Kiev Zoo (Peremohy Avenue), Ukraine, and was kept there until it died at a documented chronological age of 48 years. The female died because of its age, which indicates it was kept in good conditions adequate to the requirements of this species. Photographs and micrographs with radiological documentation were taken on the said tooth. Its structural characteristics were determined, and on the occlusal surface areas and points of anatomical constitution of its crown were identified. The tooth was also histologically evaluated via sections taken horizontally in a mesial-distal plane through the crown, horizontally in a mesial-distal plane through the coronal portion of the root, and longitudinally in a lingual-buccal plane through the crown and the root. Preparations with ground sections were made and observed in white, polarized, and reflected light. In the subsequent stage X-ray and SEM imaging has also been used, for analysis of the distribution of annual growth layers of mineralized dental tissues of cement and dentine, counted from the root canal center to the buccal surface. An attempt was also made to confirm the annual season in which the animal died, based on cement growth lines. It was observed that the growth lines were visible in all the analyzed sections, in dentine and cement. In the cement, the lines were relatively few and did not represent the attested age of the animal. The analysis of the coloration of the cement lines indicated that the animal was regularly fed a diet that was not seasonally differentiated. From the X-ray examination comes a conclusion that the animal did not suffer from periodontal diseases. Visible growth lines were observed on the dentine. On the horizontal section through the crown growth lines in the dentine were few and unclear. On the longitudinal section, both on the caudal and rostral roots, these lines were clearly visible and much more numerous than expected considering the known age of the animal, as more than 50 were counted. On horizontal sections through the upper part of both roots, distinct growth lines were observed in the dentine, and their number-48 for both roots-corresponded precisely to the age of the animal. The results of our study indicate that this method has significant potential for application to verify the age at death for modern and fossil representatives of rhinoceros.

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While thiol-based catalysts are widely employed for chemical protein synthesis relying on peptide thioester chemistry, this is less true for selenol-based catalysts whose development is in its infancy. In this study, we compared different selenols derived from the selenocysteamine scaffold for their capacity to promote thiol-thioester exchanges in water at mildly acidic pH and the production of peptide thioesters from bis(2-sulfanylethyl)amido (SEA) peptides. The usefulness of a selected selenol compound is illustrated by the total synthesis of a biologically active human chemotactic protein, which plays an important role in innate and adaptive immunity.

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