Study of tetraphenylporphyrins as modifiers of insulin amyloid aggregation

Amyloid fibrils are rigid β‐pleated protein aggregates that are connected with series of harmful diseases and at the same time are promising as base for novel nanomaterials. Thus, design of compounds able to inhibit or redirect those aggregates formation is important both for the biomedical aims and for nanotechnology applications. Here, we studied the effect of tetraphenylporphyrins (metal free, their Cu and Pd complexes, and those functionalized by carboxy and amino groups on periphery) on insulin amyloid self‐assembling. The strongest impact on insulin aggregation was demonstrated by a metal‐free porphyrin bearing four carboxy groups. This compound strongly suppresses insulin aggregation (about 88% reduction in amyloid‐sensitive probe emission) inducing formation of fibrils with the length close to this of free insulin (1.7 ± 0.6 μm as compared with 1.4 ± 0.4 μm, respectively) with an essentially reduced tendency to lateral aggregation. Contrarily, the presence of tetraphenylporphyrin containing four amino groups only slightly affects fibrils' morphology and makes weaker impact on insulin aggregation yield (about 44% reduction). This is explained by the ability of aromatic carboxy groups of 5,10,15,20‐(tetra‐4‐carboxyphenyl)porphyrin to interact with complementary protein‐binding groups and thus stabilize the supramolecular complex. For 5,10,15,20‐(tetra‐4‐aminophenyl)porphyrin, full protonation takes place in acidic medium of protein aggregation reaction; this results in the high positive charge of TPPN4 (equal or close to +6) and hence higher contribution of coulombic repulsion to interaction of TPPN4 with insulin. One more possible mechanism of the lower inhibition effect of TPPN4 as compared with TPPC4 could be the more restricted possibility of the former as compared with the latter to form H bonds with insulin groups. It was also shown that metal‐free, Pd‐containing, and Cu‐containing tetraphenylporphyrins without peripheral substituents make almost the same impact on the protein self‐assembling. We suppose this to be due to coordination saturation of these metal atoms.     

Protist Diversity and Seasonal Dynamics in Skagerrak Plankton Communities as Revealed by Metabarcoding and Microscopy

Protist community composition and seasonal dynamics are of major importance for the production of higher trophic levels, such as zooplankton and fish. Our aim was to reveal how the protist community in the Skagerrak changes through the seasons by combining high‐throughput sequencing and microscopy of plankton collected monthly over two years. The V4 region of the 18S rRNA gene was amplified by eukaryote universal primers from the total RNA/cDNA. We found a strong seasonal variation in protist composition and proportional abundances, and a difference between two depths within the euphotic zone. Highest protist richness was found in late summer‐early autumn, and lowest in winter. Temperature was the abiotic factor explaining most of the variation in diversity. Dinoflagellates was the most abundant and diverse group followed by ciliates and diatoms. We found about 70 new taxa recorded for the first time in the Skagerrak. The seasonal pattern in relative read abundance of major phytoplankton groups was well in accordance with microscopical biovolumes. This is the first metabarcoding study of the protist plankton community of all taxonomic groups and through seasons in the Skagerrak, which may serve as a baseline for future surveys to reveal effects of climate and environmental changes.     

Studies of anti-fibrillogenic activity of phthalocyanines of zirconium containing out-of-plane ligands

Series of phthalocyanines of zirconium containing lysine, citric, nonanoic acid residues and dibenzolylmethane groups as out-of-plane ligands are firstly studied as inhibitors of fibrillogenesis using cyanine-based fluorescent inhibitory assay. It was shown that studied phthalocyanines at concentration of 20μM inhibited aggregation reaction on 38.5-57.6% and inhibitory activity of phthalocyanines depended on the chemical nature of out-of-plane ligand. For the most active compound PcZrLys(2) (zirconium phthalocyanine containing lysine fragment) the efficient inhibitor concentration was estimated to be 37μM. AFM studies have shown that in the presence of PcZrLys(2) the inhibition of fibrils formation and formation of spherical oligomeric aggregates took place. Due to the ability of phthalocyanines to decrease efficiently protein aggregation into the amyloid fibrils, modification of phthalocyanine molecules via out-of-plane substitutions was proposed as approach for design of anti-fibrillogenic agents with required properties.     

Missense mutation in the amino terminus of phytochrome A disrupts the nuclear import of the photoreceptor

Phytochromes are the red/far-red photoreceptors in higher plants. Among them, phytochrome A (PHYA) is responsible for the far-red high-irradiance response and for the perception of very low amounts of light, initiating the very-low-fluence response. Here, we report a detailed physiological and molecular characterization of the phyA-5 mutant of Arabidopsis (Arabidopsis thaliana), which displays hyposensitivity to continuous low-intensity far-red light and shows reduced very-low-fluence response and high-irradiance response. Red light-induced degradation of the mutant phyA-5 protein appears to be normal, yet higher residual amounts of phyA-5 are detected in seedlings grown under low-intensity far-red light. We show that (1) the phyA-5 mutant harbors a new missense mutation in the PHYA amino-terminal extension domain and that (2) the complex phenotype of the mutant is caused by reduced nuclear import of phyA-5 under low fluences of far-red light. We also demonstrate that impaired nuclear import of phyA-5 is brought about by weakened binding affinity of the mutant photoreceptor to nuclear import facilitators FHY1 (for FAR-RED ELONGATED HYPOCOTYL1) and FHL (for FHY1-LIKE). Finally, we provide evidence that the signaling and degradation kinetics of constitutively nuclear-localized phyA-5 and phyA are identical. Taken together, our data show that aberrant nucleo/cytoplasmic distribution impairs light-induced degradation of this photoreceptor and that the amino-terminal extension domain mediates the formation of the FHY1/FHL/PHYA far-red-absorbing form complex, whereby it plays a role in regulating the nuclear import of phyA.     

Trimethine cyanine dyes as fluorescent probes for amyloid fibrils: The effect of N,N′-substituents

The effect of various N,N′-substituents in the molecule of benzothiazole trimethine cyanine dye on its ability to sense the amyloid aggregates of protein was studied. The dyes are low fluorescent when free and in the presence of monomeric proteins, but their emission intensity sharply increases in complexes with aggregated insulin and lysozyme, with the fluorescence quantum yield reaching up to 0.42.     

Effects of missense mutation on structure and function of photoreceptor

Phytochromes (PHYs) are photoreceptors of the red (R ~660  nm) and far-red (FR ~730 nm) light, and they control a wide range of responses affecting crucial aspects of plant life. There are five genes PHYA-PHYE encoding for phytochromes of different but overlapping function. One of these, PHYA has the unique function controlling specific responses in high irradiance far-red, as well as in very weak light. Appropriate PHYA functioning requires not only the photoreversibility of molecule but also the proper nuclear localization and degradation of receptor. Recently, we identified and described a mutant PHYA allele (phyA-5) in Arabidopsis thaliana, which showed reduced binding affinity to FHY1/FHL, the proteins regulating its nuclear transport, resulting in impaired nuclear localization and altered signaling under certain conditions. We present here a hypothesis to explain how the identified amino acid substitution may lead to structural changes manifested as altered signaling and phenotype displayed by the phyA-5 mutant.     

Quaternary organization of the human eEF1B complex reveals unique multi-GEF domain assembly

Protein synthesis in eukaryotic cell is spatially and structurally compartmentalized that ensures high efficiency of this process. One of the distinctive features of higher eukaryotes is the existence of stable multi-protein complexes of aminoacyl-tRNA synthetases and translation elongation factors. Here, we report a quaternary organization of the human guanine-nucleotide exchange factor (GEF) complex, eEF1B, comprising α, β and γ subunits that specifically associate into a heterotrimeric form eEF1B(αβγ)₃. As both the eEF1Bα and eEF1Bβ proteins have structurally conserved GEF domains, their total number within the complex is equal to six. Such, so far, unique structural assembly of the guanine-nucleotide exchange factors within a stable complex may be considered as a ‘GEF hub’ that ensures efficient maintenance of the translationally active GTP-bound conformation of eEF1A in higher eukaryotes.     

The parmodulin NRD-21 is an allosteric inhibitor of PAR1 Gq signaling with improved anti-inflammatory activity and stability

Novel analogs of the allosteric, biased PAR1 ligand ML161 (parmodulin 2, PM2) were prepared in order to identify potential anti-thrombotic and anti-inflammatory compounds of the parmodulin class with improved properties. Investigations of structure-activity relationships of the western portion of the 1,3-diaminobenzene scaffold were performed using an intracellular calcium mobilization assay with endothelial cells, and several heterocycles were identified that inhibited PAR1 at sub-micromolar concentrations. The oxazole NRD-21 was profiled in additional detail, and it was confirmed to act as a selective, reversible, negative allosteric modulator of PAR1. In addition to inhibiting human platelet aggregation, it showed superior anti-inflammatory activity to ML161 in a qPCR assay measuring the expression of tissue factor in response to the cytokine TNF-alpha in endothelial cells. Additionally, NRD-21 is much more plasma stable than ML161, and is a promising lead compound for the parmodulin class for anti-thrombotic and anti-inflammatory indications.