Small-angle neutron scattering, dielectric spectroscopy, and dynamic mechanical analysis data are reported for composites of isotactic polypropylene (IPP) with graphene nanoparticles (GNP) and nanographite. In various samples, the volume of the IPP matrix with a high degree of crystallinity contains GNP with concentrations of 0.7 and 1.8 wt

Hydrogels are soft and wet materials which require enhanced mechanical properties and toughness. For this aim, double-network hydrogels were prepared from soft network of covalently crosslinked hydroxypropyl guar and hard self-assembled network of carboxymethylated cellulose nanocrystals (CNCs) reversibly crosslinked by calcium ions. The gels exhibited a dramatic enhancement of mechanical strength and toughness with increasing content of CNCs and demonstrated remarkable fatigue resistance. For the first time, a 3D-visualization of CNC network within the double-network hydrogel was achieved using cryo-electron tomography. It revealed the presence of thick, fibrillar-like aggregates composed of bundles of two to five stacked nanocrystals, which are linked to adjacent bundles at their ends. These long aggregates can be responsible for significant enhancement of mechanical properties of the hydrogels by CNCs. Also, we first demonstrate the formation of hydrophobic cross-links between individual nanocrystals or bundles when end-to-end connections involve multiple arms. They may play an important role in effective energy dissipation providing higher toughness of the gels. Visualization suggests that added polymer induces microphase separation with the formation of polymer-rich and CNC-rich microdomains. The local concentrating of CNCs within CNC-rich domains should promote the aggregation of nanocrystals and their crosslinking by calcium ions, thereby strengthening the CNC network. The ability of the prepared hydrogels for 3D printing was evaluated for the first time. It was shown that the incorporation of a rigid network into a soft one provides greater shape fidelity for hydrogels.

The Dps protein is the major DNA-binding protein of prokaryotes, which protects DNA during starvation by forming a crystalline complex. The structure of such an intracellular DNA-Dps complex is still unknown. However, the phenomenon of a decrease in the size of the Dps protein from 90 Å to 69–75 Å during the formation of a complex with DNA has been repeatedly observed, and no explanation has been given. In this work, we show that during the formation of intracellular DNA–Dps crystals, the protein transitions to another oligomeric form: from a dodecameric (of 12 monomers), which has an almost spherical shape with a diameter of 90 Å, to a trimeric (of three monomers), which has a shape close to a torus-like structure with a diameter of 70 Å and a height of 40 Å. The trimer model was obtained through the molecular dynamic modeling of the interaction of the three monomers of the Dps protein. Placement of the obtained trimer in the electron density of in vitro DNA–Dps crystal allowed for the determination of the lattice parameters of the studied crystal. This crystal model was in good agreement with the SAXS data obtained from intracellular crystals of 2-day-old Escherichia coli cells. The final crystal structure contains a DNA molecule in the through channel of the crystal structure between the Dps trimers. It was discussed that the mechanism of protein transition from one oligomeric form to another in the cell cytoplasm could be regulated by intracellular metabolites and is a simple and flexible mechanism of prokaryotic cell transition from one metabolic state to another.

Ferritin-based hybrids are large 24-subunit macromolecules of megadalton scale have prospective applications ranging from drug delivery to recombinant vaccines, however, their rational design is challenging. Here, we architectured hybrids based on ferritin subunits from Helicobacter pylori and ones fused with a homolog of the Small Ubiquitin-like Modifier protein. We firstly revealed the stochastic nature of bacterial ferritin-based hybrids self-assembly by observing a sequential range of stoichiometries at totally different sample preparation procedures: coexpression in Escherichia coli cells and pH-dependent dis/reassembly. We developed an approach of quantitative evaluation of stoichiometry distribution by using a model based on random, unambiguous, and stoichiometry-independent assembly of hexamers into 24-meric hybrid globules. We identified the presence of a heterodimer and found unexpectedly disfavored stoichiometries of hexamers, which determined the narrowing of structural diversity patterns of 24-mers and shifted the stoichiometry distribution from the random one. Our findings provide new insights into the molecular mechanisms governing the shift in structural diversity patterns of ferritin-based hybrid globules. Finally, the combination of our model system and the hexamer-based approach provides a robust platform for the rational design of ferritin-based systems, with potential applications in drug delivery, structure-based immunogen design, and beyond.

The Coarse-Grained (CG) molecular dynamics (MD) simulations were used to simulate the structural behavior of biological membranes. The CG MD simulated models cover the different membrane lipidic vesicle systems with amyloid peptides and/or cholesterol and melatonin molecules. The CG MD technique allows one to considerable extend the accessible size and time in simulations of biological systems such as lipid bilayers, big vesicles, filaments, etc, containing several hundred thousand up to multi-million particles. The structural properties of model lipid membranes (spherical-like vesicles) were studied and MD simulation data were correlated with the experimental ones (the neutron scattering in particular). The molecular systems were designed and studied to associate the experimental and model studies with the nature of the mechanisms of occurrence of Alzheimer’s disease. Under certain conditions the amyloid beta oligomer can undergo an incorrect conformational rearrangement leading to the transition of “normal” soluble peptides into a toxic conformation, while causing the formation of filamentous aggregates – insoluble rigid fibrils of large sizes, that are a sign of the disease. However, the toxic effect, which has a destructive effect on the nerve cells of the brain, is possessed already by isolated misfolded peptides born in the cell membrane.

One of the critical stages of the T-cell immune response is the dimerization of the intramembrane domains of T-cell receptors (TCR). Structural similarities between the immunosuppressive domains of viral proteins and the transmembrane domains of TCR have led several authors to hypothesize the mechanism of immune response suppression by highly pathogenic viruses: viral proteins embed themselves in the membrane and act on the intramembrane domain of the TCRalpha subunit, hindering its functional oligomerization. It has also been suggested that this mechanism is used by influenza A virus in NS1-mediated immunosuppression. We have shown that the peptide corresponding to the primary structure of the potential immunosuppressive domain of NS1 protein (G51) can reduce concanavalin A-induced proliferation of PBMC cells, as well as in vitro, G51 can affect the oligomerization of the core peptide corresponding to the intramembrane domain of TCR, using AFM and small-angle neutron scattering. The results obtained using in cellulo and in vitro model systems suggest the presence of functional interaction between the NS1 fragment and the intramembrane domain of the TCR alpha subunit. We have proposed a possible scheme for such interaction obtained by computer modeling. This suggests the existence of another NS1-mediated mechanism of immunosuppression in influenza.

We have studied the effect of calcium ions (Ca 2 + ) at various concentrations on the structure of lipid vesicles in the presence of amyloid-beta peptide A beta (25-35). In particular, we have investigated the influence of calcium ions on the formation of recently documented bicelle-like structures (BLSs) emerged as a result of A beta (25-35) triggered membrane disintegration. First, we have shown by using small-angle X-ray and neutron scattering that peptide molecules rigidify the lipid bilayer of gel phase DPPC unilamellar vesicles (ULVs), while addition of the calcium ions to the system hinders this effect of A beta (25-35). Secondly, the A beta (25-35) demonstrates a critical peptide concentration at which the BLSs reorganize from ULVs due to heating and cooling the samples through the lipid main phase transition temperature ( T m ). However, addition of calcium ions does not affect noticeably the A beta- induced formation of BLSs and their structural parameters, though the changes in peptide's secondary structure, e.g. the increased alpha-helix fraction, has been registered by circular dichroism spectroscopy. Finally, according to 31 P nuclear magnetic resonance (NMR) measurements, calcium ions do not affect the lipid-peptide arrangement in BLSs and their ability to align in the magnetic field of NMR spectrometer. The influences of various concentrations of calcium ions on the lipid-peptide interactions may prove biologically important because their local concentrations vary widely in in-vivo conditions. In the present work, calcium ions were investigated as a possible tool aimed at regulating the lipid-peptide interactions that demonstrated the disruptive effect of A beta (25-35) on lipid membranes.

Methods for targeting enzymes exhibiting anticancer properties, such as methionine gamma-lyase (MGL), have not yet been sufficiently developed. Here, we present the data describing the physico-chemical properties and cytotoxic effect of fusion protein MGL-S3 - MGL from Clostridium sporogenes translationally fused to S3 domain of the viral growth factor of smallpox. MGL-S3 has methioninase activity comparable to native MGL. In solution, MGL-S3 protein primarily forms octamers, whereas native MGL, on the contrary, usually forms tetramers. MGL-S3 binds to the surface of the neuroblastoma SH-SY5Y and epidermoid carcinoma A431 cells and, unlike native MGL, remains there and retains its cytotoxic effect after media removal. In HEK293T cells lacking EGFRs, no adhesion was recorded. Confocal fluorescence microscopy confirms the preferential adhesion of MGL-S3 to tumor cells, while it avoids getting into lysosomes. Both MGL and MGL-S3 arrest cell cycle of SH-SY5Y cells mainly in the G1 phase, while only MGL-S3 retains this ability after washing the cells.

Organelle optogenetics is an approach to control cell physiology by targeted expression of microbial rhodopsins in membranes of subcellular organelles.

In-depth study of shape of hybrid micelles in the micellar solutions of anionic surfactant potassium oleate, containing hydrophobic polymer poly(4-vinylpyridine) (P4VP) was conducted via cryo-transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS) and dynamic-light scattering of visible light (DLS). Direct visualization of the solutions with cryo-TEM evidenced the coexistence of polymer-free spherical micelles and branched rodlike hybrid micelles with mean length of 200 nm and radius of 2 nm, governed by contour length of solubilized P4VP and length of hydrophobic “tail” of potassium oleate, respectively. The formation of branches in the hybrid micelles was explained by attaching the thermodynamically unfavorable end-caps of micelles to their polymer-loaded cylindrical fragments. By SANS it was shown that the cylindrical local shape and the radius of the micelles are independent of the concentration of embedded P4VP. Relaxation processes in the solutions were investigated with DLS. Three relaxation modes were observed for hybrid micelles, similar to polymer-free wormlike micelles. Fast and medium relaxation modes were attributed to diffusion of entangled micellar chains and their segments, respectively. The slow mode was related to electrostatic repulsion between similarly charged hybrid micelles.

Ferritin is a universal protein complex responsible for iron perception in almost all living organisms and has applications from fundamental biophysics to drug delivery and structure-based immunogen design. Different platforms based on ferritin share similar technological challenges limiting their development - control of self-assembling processes of ferritin itself as well as ferritin-based chimeric recombinant protein complexes. In our research, we studied self-assembly processes of ferritin-based protein complexes under different expression conditions. We fused a ferritin subunit with a SMT3 protein tag, a homolog of human Small Ubiquitin-like Modifier (SUMO-tag), which was taken to destabilize ferritin 3-fold channel contacts and increase ferritin-SUMO subunits solubility. We first obtained the octameric protein complex of ferritin-SUMO (8xFer-SUMO) and studied its structural organization by small-angle X-ray scattering (SAXS). Obtained SAXS data correspond well with the high-resolution models predicted by AlphaFold and CORAL software of an octameric assembly around the 4-fold channel of ferritin without formation of 3-fold channels. Interestingly, three copies of 8xFer-SUMO do not assemble into 24-meric globules. Thus, we first obtained and structurally characterized ferritin-based self-assembling oligomers in a deadlock state. Deadlock oligomeric states of ferritin extend the known scheme of its self-assembly process, being new potential tools for a number of applications. Finally, our results might open new directions for various biotechnological platforms utilizing ferritin-based tools.

In addition to the well-known monomeric globular (G-actin) and polymeric fibrillar (F-actin) forms, actin can exist in the so-called inactivated form (I-actin). Hsp70 chaperon, prefoldin, and CCT chaperonin are required to obtain native globular state. In contrast, I-actin is spontaneously formed in the absence of intracellular folding machinery. I-actin can be obtained from G-actin by elimination of divalent ion, incubation in presence of small concentrations of denaturants, and by heat exposure. Since G-actin is a quasi-stationary, thermodynamically unstable form, it can gradually transform into inactivated state in the absence of chelating/denaturating agents or heat exposure, but the transition is much slower. I-actin was shown to associate into oligomers up to the molecular weight of 14-16 G-actin monomers, though the structure of these oligomers remains uncharacterized. This study employs small-angle X-ray scattering to reveal novel insights into the oligomerization process of such spontaneously formed inactivated actin. These oligomers are differentiated from F-actin through comparative analysis, highlighting a unique oligomerization pathway.

ABSTRACT Several clades of luminescent bacteria are known currently. They all contain similar lux operons, which include the genes luxA and luxB encoding a heterodimeric luciferase. The aldehyde oxygenation reaction is presumed to be catalyzed primarily by the subunit LuxA, whereas LuxB is required for efficiency and stability of the complex. Recently, genomic analysis identified a subset of bacterial species with rearranged lux operons lacking luxB . Here, we show that the product of the luxA gene from the reduced luxACDE operon of Enhygromyxa salina is luminescent upon addition of aldehydes both in vivo in Escherichia coli and in vitro. Overall, Es LuxA is much less bright compared with luciferases from Aliivibrio fischeri ( Af LuxAB) and Photorhabdus luminescens ( Pl LuxAB), and most active with medium‐chain C4–C9 aldehydes. Crystal structure of Es LuxA determined at the resolution of 2.71 Å reveals a (β/α) 8 TIM‐barrel fold, characteristic for other bacterial luciferases, and the protein preferentially forms a dimer in solution. The mobile loop residues 264–293, which form a β‐hairpin or a coil in Vibrio harveyi LuxA, form α‐helices in Es LuxA. Phylogenetic analysis shows Es LuxA and related proteins may be bacterial protoluciferases that arose prior to duplication of the luxA gene and its speciation to luxA and luxB in the previously described luminescent bacteria. Our work paves the way for the development of new bacterial luciferases that have an advantage of being encoded by a single gene.

Basing on the data of small-angle neutron scattering for the nanocomposite composed of fullerene C60 (16.5 wt. %) in the matrix of isotactic polypropylene, we received information on clusterization of nanoparticles and defined their geometric parameters and dimensionality. In this paper, we propose interpretation of particle aggregation possessing the properties of surface fractal in the size range up to 80 nm observed using small-angle neutron scattering method. Basing on the well-known theories of defect structures of a fullerene molecule C60 in non-Euclidean metrics, in particular, of disclinations and monopole in two-dimensional spherical Gödel space—time, we formulate a lattice version for the action of monopole gas, in which with the lattice Monte Carlo method, using abelian projection, we estimate the energy of monopole currents at different monopole concentrations. In frames of the proposed model, it is possible to calculate fractal properties of the fullerene C60 in a polymer composite and also to interpret evolution of disclinations.

The 1-anilino-8-naphthalenesulfonate (ANS) fluorescent dye is widely used in protein folding studies due to the significant increase in its fluorescence quantum yield upon binding to protein hydrophobic regions that become accessible during protein unfolding. However, when modeling cellular macromolecular crowding conditions in protein folding experiments in vitro using crowding agents with guanidine hydrochloride (GdnHCl) as the denaturant, the observed changes in ANS spectral characteristics require careful consideration. This study demonstrates that crowding agents can form clusters that interact differently with ANS. Furthermore, GdnHCl can disrupt these clusters and directly affect the ANS spectral characteristics. A model for the interaction between GdnHCl, crowders, and ANS is proposed. Using bovine serum albumin (BSA) as a model protein, the limitations of using ANS for studying conformational transitions induced by GdnHCl in the presence of crowding agents are demonstrated.

Results of experiments on small-angle scattering of neutrons and X-rays on colloidal suspensions with anisometric barium hexaferrite nanoparticles in an aqueous solvent are reported. It has been shown that the preparation according to a new method produces fairly stable colloids with two types of particles of reproducible morphology and size: large lamellar-shaped particles ( 100 nm) with a thickness of 7 nm and small isometric particles with a size of 6 nm.

Dual networks formed by entangled polymer chains and wormlike surfactant micelles have attracted increasing interest in their application as thickeners in various fields since they combine the advantages of both polymer- and surfactant-based fluids. In particular, such polymer-surfactant mixtures are of great interest as novel hydraulic fracturing fluids with enhanced properties. In this study, we demonstrated the effect of the chemical composition of an uncharged polymer poly(vinyl alcohol) (PVA) and pH on the rheological properties and structure of its mixtures with a cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride already exploited in fracturing operations. Using a combination of several complementary techniques (rheometry, cryo-transmission electron microscopy, small-angle neutron scattering, and nuclear magnetic resonance spectroscopy), we showed that a small number of residual acetate groups (2–12.7 mol%) in PVA could significantly reduce the viscosity of the mixed system. This result was attributed to the incorporation of acetate groups in the corona of the micellar aggregates, decreasing the molecular packing parameter and thereby inducing the shortening of worm-like micelles. When these groups are removed by hydrolysis at a pH higher than 7, viscosity increases by five orders of magnitude due to the growth of worm-like micelles in length. The findings of this study create pathways for the development of dual semi-interpenetrating polymer-micellar networks, which are highly desired by the petroleum industry.

HYPOTHESIS:The formation of micellar aggregates and the changes in their morphology are crucial for numerous practical applications of surfactants. However, a proper structural characterization of complicated micellar nanostructures remains a challenge. This paper demonstrates the advances of cryo-electron tomography (cryo-ET) in revealing the structural characteristics that accompany the evolution of surfactant aggregates. EXPERIMENTS:By using cryo-ET in combination with cryo-transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS), and rheometry, studies were carried out on a model system composed of zwitterionic and nonionic surfactants. In this system, the molecular packing parameter was increased gradually by increasing the molar fraction of nonionic surfactant. FINDINGS:A series of structural transformations was observed: linear wormlike micelles (WLMs) → branched WLMs → saturated network of multiconnected WLMs → perforated vesicles (stomatosomes). The transformations occur through an increase in the number of branches at the expense of cylindrical subchains and semispherical endcaps. Exponential distribution of subchains length was confirmed experimentally for multiconnected saturated networks. The stomatosomes were formed when the length of subchains becomes much shorter than the persistence length, causing the three-dimensional (3D) structure to transform into a two-dimensional (2D) membrane. This work identifies the mechanism of the structural changes, which can be further used to design various surfactant self-assemblies.

Small-angle neutron scattering has been used to study the mechanisms of graphene oxide self-organization in aqueous dispersions during its interaction with detonation nanodiamonds having different surface potential signs. Being mixed with a hydrosol of positively charged diamonds, negatively charged graphene oxide yields a stable colloid due to the formation of planar heterostructures in the form of paired sheets tightly connected through diamonds (25 wt

Based on small angle neutron-scattering data from a nanocomposite composed of fullerene C60 (16.5 wt