Search Results (1,318)

AAA+ ATPases are ring-shaped hexameric protein complexes that operate as elaborate macromolecular motors, driving a variety of ATP-dependent cellular processes. AAA+ ATPases undergo large-scale conformational changes that lead to the conversion of chemical energy from ATP into mechanical work to perform a wide range of functions, such as unfolding and translocation of the protein substrate inside a proteolysis chamber of an AAA+-associated protease. Despite extensive biochemical studies on these macromolecular assemblies, the mechanism of substrate unfolding and degradation has long remained elusive. Indeed, until recently, structural characterization of AAA+ protease complexes remained hampered by the size and complexity of the machinery, harboring multiple protein subunits acting together to process proteins to be degraded. Additionally, the major structural rearrangements involved in the mechanism of this complex represent a crucial challenge for structural biology. Here, we report the main advances in deciphering molecular details of the proteolytic reaction performed by AAA+ proteases, based on the remarkable progress in structural biology techniques. Particular emphasis is placed on the latest findings from high-resolution structural analysis of the ClpXP proteolytic complex, using crystallographic and cryo-EM investigations. In addition, this review presents some additional dynamic information obtained using solution-state NMR. This information provides molecular details that help to explain the protein degradation process by such molecular machines. Full article

To rationally utilize and develop agricultural waste products, this research involved the synthesis of degradable high water-absorbing resin through the graft copolymerization of cotton straw (CS) with monomers. Among them, acrylic acid (AA) and acrylamide (Am) are used as grafting copolymer monomers, cellulose in the straw serves as the network framework, and MBA acts as the crosslinking agent. ⁶⁰Co gamma rays as initiators. Different concentrations of alkaline solution were used to dissolve the cellulose in the straw. Single-factor and orthogonal experiments were conducted to optimize the experimental conditions. various analytical methods such as thermogravimetric analysis (TG), X-ray crystallography (XRD), infrared spectroscopy (IR), and scanning electron microscopy (SEM) were employed to characterize the structure and properties of the product. ⁶⁰Co gamma rays as initiators, can reduce the pollution caused by chemical initiators and lower energy consumption. Through this research, agricultural waste can be effectively utilized, reducing environmental pollution, lowering industrial energy consumption, and synthesizing degradable and environmentally friendly high-absorbent resins. The product can be applied to agricultural water retention agent, fertilizer controlled release agent and other aspects. Full article

Heterocycles—cyclic compounds containing at least one non-carbon heteroatom (e.g., N, O, S)—are fundamental in medicinal chemistry due to their influence on a drug’s physicochemical and biological properties. They improve solubility, bioavailability, and facilitate molecular recognition through their electronic and hydrogen-bonding features. These properties make them indispensable in drug design. This study focuses on the synthesis of a key heterocyclic intermediate: benzyl-N-[4-(2-hydroxyethyl)-1,3-thiazol-2-yl]carbamate. This molecule incorporates a thiazole ring, known for its rigidity and electronic properties, that enhances target interactions. The 2-position bears a Cbz-protected amine, enabling orthogonal deprotection, while the 4-position features a hydroxyethyl side chain, providing a handle for further chemical modifications via nucleophilic substitution. Herein, we report the successful synthesis of this intermediate along with its full ¹H and ¹³C NMR spectra, melting point, and crystal structure, confirming its identity and purity. Full article

The search for substances that increase the immunity of bees is becoming a necessity in the era of various environmental threats and the declining immunocompetence of these insects. Therefore, we tested the biological and physicochemical properties of 7-diethylamino-4-hydroxycoumarin (7DOC). In a cage test, two groups of bees were created: a control group fed with sugar syrup and an experimental group fed with sugar syrup with the addition of 7DOC. In each group, the longevity of the bees was determined and the protein concentrations and antioxidant activities in the bees’ hemolymph were determined. The bees fed with 7DOC lived 2.7 times longer than those in the control group. The protein concentrations and activities of SOD, CAT, GPx and GST, as well as the TAC levels, were significantly higher in the hemolymph of the supplemented workers. To confirm these potent biological properties of 7DOC, the UV-Vis spectra, emission and excitation of fluorescence, synchronous spectra and finally the fluorescence lifetimes of this compound were measured using the time-correlated single photon counting method, in various environments differing in polarity and in the environment applied in bee research. This compound was shown to be sensitive to changes in solvent polarity. The spectroscopic assays were complemented with crystallographic tests of the obtained monocrystals of the aforementioned compounds, which attested to the aggregation effects observed in the spectra measurements for the selected coumarin. The research results confirm that this compound has the potential to be implemented in apiary management, which will be our application goal, but further research into apiary conditions is required. Full article

Searching for new and efficient transfer hydrogenation catalysts, a series of new organometallic ruthenium(II)-arene complexes of the formulae [Ru(η⁶-p-cymene)(L)Cl][PF₆] (1–8) and [Ru(η⁶-p-cymene)(L)Cl][Ru(η⁶-p-cymene)Cl₃] (9–11) were synthesized and fully characterized. These were prepared from the reaction of pyridine–quinoline and biquinoline-based ligands (L) with [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂, in 1:2 and 1:1, metal (M) to ligand (L) molar ratios. Characterization includes a combination of spectroscopic methods (FT-IR, UV-Vis, multi nuclear NMR), elemental analysis and single-crystal X-ray crystallography. The pyridine–quinoline organic entities encountered, were prepared in high yield either via the thermal decarboxylation of the carboxylic acid congeners, namely 2,2′-pyridyl-quinoline-4-carboxylic acid (pqca), 8-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (8-Mepqca), 6′-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (6′-Mepqca) and 8,6′-dimethyl-2,2′-pyridyl-quinoline-4-carboxylic acid (8,6′-Me₂pqca), affording the desired ligands pq, 8-Mepq, 6′-Mepq and 8,6′-Me₂pq, or by the classical Friedländer condensation, to yield 4,6′-dimethyl-2,2′-pyridyl-quinoline (4,6′-Me₂pq) and 4-methyl-2,2′-pyridyl-quinoline (4-Mepq), respectively. The solid-state structures of complexes 1–4, 6, 8 and 9 were determined showing a distorted octahedral coordination geometry. The unit cell of 3 contains two independent molecules (Ru-3), (Ru′-3) in a 1:1 ratio, due to a slight rotation of the arene ring. All complexes catalyze the transfer hydrogenation of acetophenone, using 2-propanol as a hydrogen donor in the presence of KOiPr. Among them, complexes 1 and 5 bearing methyl groups at the 8 and 4 position of the quinoline moiety, convert acetophenone to 1-phenylethanol quantitatively, within approximately 10 min with final TOFs of 1600 h⁻¹. The catalytic performance of complexes 1–11, towards the transfer hydrogenation of p-substituted acetophenone derivatives and benzophenone, ranges from moderate to excellent. An inner-sphere mechanism has been suggested based on the detection of ruthenium(II) hydride species. Full article

In this study, 3-chlorothiophene-2-carboxylic acid (HL) was used as a main ligand to successfully synthesize four novel complexes: [Cu(L)₂(Py)₂(OH₂)₂] (1), [Co(L)₂(Py)₂(OH₂)₂] (2) (Py = pyridine), [{Ni(L)₂(OH₂)₄}₂{Ni(L)(OH₂)₅}]L•5H₂O (3), and [{Co(L)₂(OH₂)₄}₂{Co(L)(OH₂)₅}]L•5H₂O (4). All four compounds were identified by elemental analysis and ESI mass spectrometry, and subsequently characterized by IR spectroscopy, UV-visible diffuse reflectance spectroscopy, electron paramagnetic resonance spectroscopy, thermogravimetric analysis, single-crystal X-ray crystallography, and cyclic voltammetry. X-ray analyses revealed that complexes 1 and 2 exhibit a centrosymmetric pseudo-octahedral coordination geometry; the copper (II) and cobalt (II) metal ions, respectively, are located at the crystallographic center of inversion. The coordination sphere of the copper (II) complex is axially elongated in accordance with the Jahn–Teller effect. Intriguingly, for charge neutrality, compounds 3 and 4 crystallized as three independent mononuclear octahedrally coordinated metal centers, which are two $\left[\mathrm{M}{\mathrm{L}}_2{\left({\mathrm{O}\mathrm{H}}_2\right)}_4\right]$ complex molecules and one ${\left[\mathrm{M}\mathrm{L}{\left({\mathrm{O}\mathrm{H}}_2\right)}_5\right]}^{+}$ complex cation (M = ${\mathrm{N}\mathrm{i}}^{\mathrm{I}\mathrm{I}}$ and ${\mathrm{C}\mathrm{o}}^{\mathrm{I}\mathrm{I}}$, respectively), with the ligand anion ${\mathrm{L}}^{-}$ serving as the counter ion. The anticancer activities of these complexes were systematically assessed on human leukemia K562 cells, lung cancer A549 cells, liver cancer HepG2 cells, breast cancer MDA-MB-231 cells, and colon cancer SW480 cells. Among them, complex 4 shows significant inhibitory effects on leukemia K562 cells and colon cancer SW480 cells. Full article

Fungal cell walls, composed of polysaccharides and proteins, play critical roles in adaptation, cell division, and protection against environmental stress. Their polyglucan components are continuously remodeled by various types of glycosyl hydrolases (GHs) and transferases (GTs). In Saccharomyces cerevisiae and other ascomycetes, enzymes of the Dfg5 subfamily, which belong as GTs to the GH76 family, cleave an α1,4 linkage between glucosamine and mannose to facilitate covalent linkage of GPI-anchored proteins to the cell wall’s polyglucans. In contrast, the functions of other fungal GH76 subfamilies are not understood. We characterized CtGH76 from the sordariomycete Chaetomium thermophilum, a member of the Fungi/Bacteria-mixed GH76 subfamily, revealing conserved structural features and functional divergence within the GH76 family. Notably, our structural characterization by X-ray crystallography combined with glycan fragment screening indicated that CtGH76 can recognize GPI-anchors like members of the Dfg5 subfamily but shows a broader promiscuity toward other glycans with central α1,6-mannobiose motifs due to the presence of an elongated glycan-binding canyon. These findings provide new insights into GH76 enzyme diversity and fungal cell wall maturation. Full article

Fluorescent chemosensors are increasingly becoming relevant in recognition chemistry due to their sensitivity, selectivity, fast response time, real-time detection capability, and low cost. Boronic acids have been reported for the recognition of mycolactone, the cytotoxin responsible for tissue damage in Buruli ulcer disease. A library of fluorescent arylboronic acid chemosensors with various signaling moieties with certain beneficial photophysical characteristics (i.e., aminoacridine, aminoquinoline, azo, BODIPY, coumarin, fluorescein, and rhodamine variants) and a recognition moiety (i.e., boronic acid unit) were rationally designed and synthesised using combinatorial approaches, purified, and fully characterised using a set of complementary spectrometric and spectroscopic techniques such as NMR, LC-MS, FT-IR, and X-ray crystallography. In addition, a complete set of basic photophysical quantities such as absorption maxima (λ_abs^max), emission maxima (λ_em^max), Stokes shift (∆λ), molar extinction coefficient (ε), fluorescence quantum yield (Φ_F), and brightness were determined using UV-vis absorption and fluorescence emission spectroscopy techniques. The synthesised arylboronic acid chemosensors were investigated as chemosensors for mycolactone detection using the fluorescent-thin layer chromatography (f-TLC) method. Compound 7 (with a coumarin core) emerged the best (λ_abs^max = 456 nm, λ_em^max = 590 nm, ∆λ = 134 nm, ε = 52816 M⁻¹cm⁻¹, Φ_F = 0.78, and brightness = 41,197 M⁻¹cm⁻¹). Full article

Target compound 3′H-spiro[dibenzo[c,h]xanthene-7,1′-isobenzofuran]-3′-one (1) has long been known to be a by-product obtained from the preparation of naphtholphthalein. The structure of compound 1 was elucidated in the early 20th century; however, this compound has not previously been fully characterized using modern techniques. In this report, ¹H NMR and ¹³C NMR spectra are provided. X-ray crystallography is also used to characterize the title compound for the first time. Full article

Nine chaetoglobosins (1–9) including five previously undescribed ones (1–5) were obtained from the culture broth of an endophytic fungus (Chaetomium sp. UJN-EF006) isolated from the leaves of Vaccinium bracteatum. The structures of these fungal metabolites were elucidated by spectroscopic methods including mass spectroscopy, nuclear magnetic resonance, single crystal X-ray crystallography, and electronic circular dichroism. To accelerate the development of novel fungicides, all of the isolated chaetoglobosins were evaluated for their antifungal activity against two crop pathogens, Botrytis cinerea and Sclerotinia sclerotiorum. The assay results revealed that chaetoglobosins 2, 6, 7, and 9 possessed a significant fungicidal effect against B. cinerea, with EC₅₀ values all below 10 μg/mL. Particularly, the most potent compound, 7, was 175- and 96-fold as active as the commercially available fungicides carbendazim (EC₅₀ 70.11 μg/mL) and azoxystrobin (EC₅₀ 39.02 μg/mL), respectively. A further observation under scanning electron microscope indicated that compound 2 could markedly impair the fungal hyphae of B. cinerea. The study demonstrates that the chaetoglobosins had excellent in vitro antifungal activities against B. cinerea. Full article

A series of novel derivatives of 3-amino-4-hydroxybenzenesulfonamide was synthesized. As the analyzed compounds possess a sulfonamide group, the affinity of these compounds for human carbonic anhydrases (CAs) was measured by fluorescent thermal shift assay, and compound selectivity for different isoenzymes was identified. The crystal structures of the complexes of compound 25 with CAI and CAII were determined. Additionally, the activity of compounds on the viability of three cancer cell lines—human glioblastoma U-87, triple-negative breast cancer MDA-MB-231, and prostate adenocarcinoma PPC-1—was established using the MTT assay and compared to CAIX-selective and non-selective comparative compounds U-104 and acetazolamide. The half-maximal concentration (EC₅₀) was determined for the identified most active compounds, and their selectivity over fibroblasts was established. Compound 9 (inhibitor of multi-CAs) and compound 21 (not binding to CAs), considered the most promising candidates, were tested in cancer cell 3D cultures (cancer spheroids) by assessing their effect on spheroid growth and viability. Both compounds reduced the viability of spheroids from all cancer cell lines. U-87 and PPC-1 spheroids became looser in the presence of compound 9, while the growth of MDA-MB-231 spheroids was slower compared to the control. Compound 21 reduced the growth of U-87 and MDA-MB-231 3D cultures, with no significant effect on PPC-1 spheroids. Full article

We report the first syntheses—from commercially available 3-chloro-2-fluoroprop-1-ene (9)—of key garlic-derived compounds containing sp²-fluorine. We also report synthesis of fluoro-5,6-dihydrothiopyrans by trapping 2-fluorothioacrolein (15). Thus, difluoroallicin (12, S-(2-fluoro-2-propenyl) 2-fluoroprop-2-ene-1-sulfinothioate) is prepared by peracid oxidation of 1,2-bis(2-fluoro-2-propenyl)disulfane (11). S-2-Fluoro-2-propenyl-l-cysteine (2-fluorodeoxyalliin, 13), synthesized from cysteine and characterized by X-ray crystallography, is oxidized to its S-oxide, 2-fluoroalliin (22). The latter, with alliinase-containing powdered fresh garlic, gives a mixture of 12, allicin (1), and isomers of monofluoroallicin (23), indicating that 22 serves as a substrate for garlic alliinase. Upon heating, 12 generates transient 15, which dimerizes giving difluoro vinyl dithiins 6 and 7. Ethyl acrylate trapping of 15 affords 5- and 6-substituted 3-fluoro-5,6-dihydro-4H-thiopyrans (19 and 20). In 1,1,1,3,3,3-hexafluoro-2-propanol (HEFP) as solvent, 12 is converted into trifluoroajoene ((E,Z)-1-(2-fluoro-3-((2-fluoro-2-propenyl)sulfinyl)prop-1-en-1-yl)-2-(2-fluoro-2-propenyl)disulfane; 18). Liquid sulfur converts 11 to a (CH₂=CFCH₂)₂S_n mixture (n = 4–15), characterized by UPLC-(Ag⁺)-coordination ion spray-mass spectrometry. Full article

The ReAV enzyme from Rhizobium etli, a representative of Class 3 L-asparaginases, is sequentially and structurally different from other known L-asparaginases. This distinctiveness makes ReAV a candidate for novel antileukemic therapies. ReAV is a homodimeric protein, with each subunit containing a highly specific zinc-binding site created by two cysteines, a lysine, and a water molecule. Two Ser-Lys tandems (Ser48-Lys51, Ser80-Lys263) are located in the close proximity of the metal binding site, with Ser48 hypothesized to be the catalytic nucleophile. To further investigate the catalytic process of ReAV, site-directed mutagenesis was employed to introduce alanine substitutions at residues from the Ser-Lys tandems and at Arg47, located near the Ser48-Lys51 tandem. These mutational studies, along with enzymatic assays and X-ray structure determinations, demonstrated that substitution of each of these highly conserved residues abolished the catalytic activity, confirming their essential role in enzyme mechanism. Full article

Acetone carboxylase (AC) from Xanthobacter autotrophicus is a 360 KDa α₂β₂γ₂ heterohexamer that catalyzes the ATP-dependent formation of phosphorylated acetone and bicarbonate intermediates that react at Mn(II) metal active sites to form acetoacetate. Structural models of X. autotrophicus AC (XaAC) with and without nucleotides reveal that the binding and phosphorylation of the two substrates occurs ~40 Å from the Mn(II) active sites where acetoacetate is formed. Based on the crystal structures, a significant conformational change was proposed to open and close a tunnel that facilitates the passage of reaction intermediates between the sites for nucleotide binding and phosphorylation of substrates and Mn(II) sites of acetoacetate formation. We have employed electron paramagnetic resonance (EPR), kinetic assays, and hydrogen/deuterium exchange mass spectrometry (HDX-MS) of poised ligand-bound states and site-specific amino acid variants to complete an in-depth analysis of Mn(II) coordination and allosteric communication throughout the catalytic cycle. In contrast with the established paradigms for carboxylation, our analyses of XaAC suggested a carboxylate shift that couples both local and long-range structural transitions. Shifts in the coordination mode of a single carboxylic acid residue (αE89) mediate both catalysis proximal to a Mn(II) center and communication with an ATP active site in a separate subunit of a 180 kDa α₂β₂γ₂ complex at a distance of 40 Å. This work demonstrates the power of combining structural models from X-ray crystallography with solution-phase spectroscopy and biophysical techniques to elucidate functional aspects of a multi-subunit enzyme. Full article

The interaction of cobalt(II) with first-generation quinolones oxolinic acid (Hoxo), flumequine (Hflmq), pipemidic acid (Hppa) and cinoxacin (Hcx) in the presence of the N,N′-donor heterocyclic ligands 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) afforded a series of novel cobalt complexes, namely [Co(bipy)₂(oxo)](PF₆)₂·H₂O (1), [Co(phen)₂(oxo)](PF₆)₂·0.5CH₃OH·0.5H₂O (2), [Co(bipy)₂(flmq)](PF₆)₂·0.5CH₃OH·0.5H₂O (3), [Co(bipy)₂(ppa)](PF₆)₂·CH₃OH·0.5H₂O (4), [Co(phen)₂(cx)](PF₆)₂·CH₃OH·0.5H₂O (5), and [Co(phen)₂(flmq)](PF₆)·0.5CH₃OH·H₂O (6). The characterization of the complexes involved physicochemical techniques, various spectroscopies and single-crystal X-ray crystallography. The affinity of complexes to calf-thymus (CT) DNA was monitored with various techniques, suggesting intercalation in-between the DNA-nucleobases as the most probable interaction mode, which may be combined with electrostatic interactions as a result of the cationic nature of the complexes. The affinity of the complexes for bovine and human serum albumin proteins was monitored, and the determined corresponding albumin-binding constants revealed a tight and reversible interaction. Full article