Discovery of the Lanthipeptide Curvocidin and Structural Insights into its Trifunctional Synthetase CuvL

Lanthipeptides are ribosomally-synthesized natural products from bacteria featuring stable thioether-crosslinks and various bioactivities. Herein, we report on a new clade of tricyclic class-IV lanthipeptides with curvocidin from Thermomonospora curvata as its first representative. We obtained crystal structures of the corresponding lanthipeptide synthetase CuvL that showed a circular arrangement of its kinase, lyase and cyclase domains, forming a central reaction chamber for the iterative substrate processing involving nine catalytic steps. The combination of experimental data and artificial intelligence-based structural models identified the N-terminal subdomain of the kinase domain as the primary site of substrate recruitment. The ribosomal precursor peptide of curvocidin employs an amphipathic α-helix in its leader region as an anchor to CuvL, while its substrate core shuttles within the central reaction chamber. Our study thus reveals general principles of domain organization and substrate recruitment of class-IV and class-III lanthipeptide synthetases.     

The role of post-translational modifications for learning and memory formation

Learning and memory depend on molecular mechanisms involving the protein machinery. Recent evidence proposes that post-translational modifications (PTMs) play a major role in these cognitive processes. PTMs including phosphorylation of serine, threonine, and tyrosine are already well-documented to play a role for synaptic plasticity of the brain, neurotransmitter release, vesicle trafficking and synaptosomal or synaptosomal-associated proteins are substrates of a series of specific protein kinases and their counterparts, protein phosphatases. But protein phosphorylation is only one out of many possible PTMs and first work shows a role of palmitoylation as well as glycosylation for proteins involved in memory formation. Recent technology may now allow reliable detection and even quantification of PTMs of proteins involved in the cognitive system. This will contribute to the understanding of mechanisms for learning and memory formation at the chemical level and has to complement determination of protein levels and indeed determination of protein expression per se generates limited information. The many other PTMs expected including protein nitrosylation and alkylation will even represent targets for pharmacological interventions but in turn increase the complexity of the system. Nevertheless, determination of the presence and the function of PTMs is mandatory and promising cognitive research at the protein chemical level.     

In vitro enhancement of anticancer activity of paclitaxel by a Cremophor free cyclodextrin-based nanosponge formulation

A severe limitation for cancer therapy is the poor water solubility of many important therapeutic anticancer drugs. The development of novel delivery systems is therefore currently ongoing. We propose the use of β-cyclodextrin based nanosponges to deliver paclitaxel as an alternative to classical formulation in Cremophor EL. They are solid nanoparticles with mean diameter lower than 500?nm and spherical shape. Nanosponges show a safe profile being non-hemolytic and non cytotoxic. Nanosponges dissolved and encapsulated paclitaxel up to 2?mg/ml. The paclitaxel-loaded nanosponges formed a water stable colloidal system avoiding the recrystallization of paclitaxel. The in vitro release studies showed an almost complete release in 2?h without initial burst effect. Our study demonstrates that delivery of paclitaxel via nanosponges increased the amount of paclitaxel entering cancer cells and lowers paclitaxel IC50, therefore enhancing its pharmacological effect. β-Cyclodextrin based nanosponges can therefore be considered an alternative system to solubilize and deliver the paclitaxel.     

An improved and fast UHPLC-PDA methodology for determination of <Emphasis Type="Italic">L</Emphasis>-ascorbic and dehydroascorbic acids in fruits and vegetables. Evaluation of degradation rate during storage

This study provides a versatile validated method to determine the total vitamin C content, as the sum of the contents of L-ascorbic acid (L-AA) and dehydroascorbic acid (DHAA), in several fruits and vegetables and its degradability with storage time. Seven horticultural crops from two different origins were analyzed using an ultra-high-performance liquid chromatographic–photodiode array (UHPLC-PDA) system, equipped with a new trifunctional high strength silica (100% silica particle) analytical column (100 mm × 2.1 mm, 1.7 μm particle size) using 0.1% (v/v) formic acid as mobile phase, in isocratic mode. This new stationary phase, specially designed for polar compounds, overcomes the problems normally encountered in HPLC and is suitable for the analysis of large batches of samples without L-AA degradation. In addition, it proves to be an excellent alternative to conventional C18 columns for the determination of L-AA in fruits and vegetables. The method was fully validated in terms of linearity, detection (LOD) and quantification (LOQ) limits, accuracy, and inter/intra-day precision. Validation experiments revealed very good recovery rate of 96.6 ± 4.4% for L-AA and 103.1 ± 4.8 % for total vitamin C, good linearity with r ² -values >0.999 within the established concentration range, excellent repeatability (0.5%), and reproducibility (1.6%) values. The LOD of the method was 22 ng/mL whereas the LOQ was 67 ng/mL. It was possible to demonstrate that L-AA and DHAA concentrations in the different horticulture products varied oppositely with time of storage not always affecting the total amount of vitamin C during shelf-life. Locally produced fruits have higher concentrations of vitamin C, compared with imported ones, but vegetables showed the opposite trend. Moreover, this UHPLC-PDA methodology proves to be an improved, simple, and fast approach for determining the total content of vitamin C in various food commodities, with high sensitivity, selectivity, and resolving power within 3 min of run analysis.     

Ab initio ground- and excited-state intermolecular potential energy surfaces for the NO-Ne and NO-Ar van der Waals complexes

The ground- [NO(X(2)Π)] and excited-state [NO(A(2)Σ(+))] intermolecular potential energy surfaces (IPESs) of the NO-Ne and NO-Ar van der Waals complexes are evaluated using the RCCSD(T) spin-restricted coupled cluster method and d-aug-cc-pVQZ basis set extended with a set of 3s3p2d1f1g midbond functions. These bases are selected from the results of a systematic basis-set convergence study carried out for the NO(A(2)Σ(+))-Ar state. We fit the interaction energies to analytic functions and compare the results to those previously available. The NO-Ar (NO-Ne) IPESs are characterized by absolute minima of -120 and -75 cm(-1) (-58 and -5 cm(-1)) at the ground and first excited state, respectively, located close to the T-shaped geometries for the ground states and at linear dispositions in the case of the excited states. The potentials are further used in the evaluation of the rovibrational spectra of the complexes, and the results are compared to those available in the literature.     

High-frequency hearing in phocid and otariid pinnipeds: an interpretation based on inertial and cochlear constraints (L)

Audiograms in air and underwater, determined by previous workers for four pinniped species, two eared seals (Otariidae) and two phocids (Phocidae), are supplemented here by measurements on their middle ear ossicular mass, enabling mechanistic interpretations of high-frequency hearing and audiogram differences. Otariid hearing is not largely affected by the medium (air/water). This indicates that cochlear constraints limit high-frequency hearing in otariids. Phocids, however, have massive middle ear ossicles, and underwater hearing has radically shifted towards higher frequencies. This suggests that the high-frequency hearing of phocids in air is constrained by ossicle inertia.     

Novel Approach of Evaluating Polymer Nanocomposite Structure by Measurements of the Freezing‐Point Depression

Summary: A novel experimental approach based on the freezing‐point depression of a solvent in a swollen gel has been developed to characterize the structure of nanocomposites. A higher depression in the freezing point has been related with an exfoliated nanocomposite. This increased depression not only depends on the formation of a tighter network but also on the decrease of the size of the solvent cages where the nucleation takes place.

The nucleation process of unfilled and organoclay‐filled natural rubber with the same crosslinking density.     

A detailed experimental and computational study of Cd complexes with pyridyl-based thiazolyl hydrazones

Interest in Cd complexes has been growing in recent years. Cd complexes are considered a potential solution in the search for novel antibiotics that can fight antimicrobial resistance. In addition, Cd complexes draw attention to material chemistry. The main objective of this work was to prepare the first Cd(II) complexes with anionic forms of pyridine-based thiazolyl hydrazone (THs) ligands HLS² [(E)-4-(4-methoxyphenyl)-2-(2-[pyridine-2-ylmethylene]hydrazinyl)thiazole] and HLS³ [(E)-2-(2-[pyridine-2-ylmethylene]hydrazinyl)-4-(p-tolyl)thiazole] and perform their structural and spectroscopic characterization, as well as stability in solution and upon heating. Studies related to their biological activities and possible electrochromic applications are also being conducted. Complexes [Cd(HLS²)₂] ( 1 ) and [Cd(HLS³)₂] ( 2 ) have been characterized by a single-crystal X-ray diffraction and computational analysis of intermolecular interactions responsible for their solid-state structures was performed. Thermal stability of 1 and 2 in the solid-state was analyzed by TGA/MS, where as their solution stability was determined by the spectrophotometric titration method. Electrochemical and in situ UV–Vis spectroelectrochemical analyses of 1 and 2 were carried out to determine redox mechanisms and the influence of the substituents and electrolytes on their redox responses. The antioxidant capacity of both complexes was tested in antioxidant assays, while their antimicrobial activity was tested against five Gram-positive and four Gram-negative bacteria, as well as against three fungi. The obtained results indicate their potent antioxidant capacity. The antimicrobial activity of investigated compounds on almost all tested bacterial strains was stronger than that of the standard antibiotic erythromycin. The results of docking studies indicate that the minor groove DNA is the possible biological target of 1 and 2 .