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Activating signal co-integrator complex 1 (ASCC1) acts with ASCC-ALKBH3 complex in alkylation damage responses. ASCC1 uniquely combines two evolutionarily ancient domains: nucleotide-binding K-Homology (KH) (associated with regulating splicing, transcriptional, and translation) and two-histidine phosphodiesterase (PDE; associated with hydrolysis of cyclic nucleotide phosphate bonds). Germline mutations link loss of ASCC1 function to spinal muscular atrophy with congenital bone fractures 2 (SMABF2). Herein analysis of The Cancer Genome Atlas (TCGA) suggests ASCC1 RNA overexpression in certain tumors correlates with poor survival, Signatures 29 and 3 mutations, and genetic instability markers. We determined crystal structures of Alvinella pompejana (Ap) ASCC1 and Human (Hs) PDE domain revealing high-resolution details and features conserved over 500 million years of evolution. Extending our understanding of the KH domain Gly-X-X-Gly sequence motif, we define a novel structural Helix-Clasp-Helix (HCH) nucleotide binding motif and show ASCC1 sequence-specific binding to CGCG-containing RNA. The V-shaped PDE nucleotide binding channel has two His-Φ-Ser/Thr-Φ (HXT) motifs (Φ being hydrophobic) positioned to initiate cyclic phosphate bond hydrolysis. A conserved atypical active-site histidine torsion angle implies a novel PDE substrate. Flexible active site loop and arginine-rich domain linker appear regulatory. Small-angle X-ray scattering (SAXS) revealed aligned KH-PDE RNA binding sites with limited flexibility in solution. Quantitative evolutionary bioinformatic analyses of disease and cancer-associated mutations support implied functional roles for RNA binding, phosphodiesterase activity, and regulation. Collective results inform ASCC1's roles in transactivation and alkylation damage responses, its targeting by structure-based inhibitors, and how ASCC1 mutations may impact inherited disease and cancer.

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Using a powerful synchrotron radiation X-ray source, we developed a cell that can perform Small Angle X-ray Scattering (SAXS) measurements under high shear (~ 105 s−1). We successfully and quantitatively visualized the deformation of polymer chains as polymer additives in oil under high shear. We found that poly(alkylmethacrylate) (PMA) with the lowest molecular weight was not deformed by the shear flow and did not show the shear thinning behavior. On the other hand, the other PMAs were deformed and exhibited shear-thinning behaviors. We compared the experimental results with the simulation by Ryder et al.(The Journal of Chemical Physics 45: 194906 (2006)) and found the shrink perpendicular to the flow direction in the experiment is stronger than that in the simulation, indicating that the rigidity of the polymer chains enhanced by long side groups induced the alignment of the chain along the flow direction. The decrease in viscosity was less than that estimated from the rate of deformation estimated by SAXS due to the effects of polydispersity of PMA polymers. [ABSTRACT FROM AUTHOR]

Among uranium extraction materials, amidoxime polymers are very promising. But the conformation of molecular chains is not well understood. Herein, conformation behavior of polyamidoxime (PAO) was analyzed via molecular dynamics. In water, the conformation of PAO is extended, its radius of gyration (Rg) is 12.5 Å. However, the Rg of polyacrylonitrile is merely 6.2 Å. The PAO conformation collapses due to uranyl and sodium ions. Moreover, small angle X-ray scattering showed that Rg from 11.6 to 11.0 nm after uranium adsorption. Overall, this work will be beneficial to the design of new uranium adsorbents. [ABSTRACT FROM AUTHOR]

In this study, the effects of incorporating arginine-modified peptide into the structure of discshaped bicelles were investigated. Characterization of bicellar system was conducted using different techniques, including dynamic light scattering (DLS), zeta potential, cryogenic transmission electron microscopy (cryo-TEM) and small angle X-ray scattering (SAXS). Bicelle skin permeability as drug carriers was also evaluated. The addition of peptides revealed formation of small-sized, stable and discoidal-shaped bicelles. Positive zeta potential and synchrotron radiation experiments confirmed the presence and showed the peptide distribution across the bicelle face and rim region. A major disruption with the lipid rearrangement of the stratum corneum and the disruption of bicelle structures by the interaction between bicelle lipids and stratum corneum lipids were observed during the application of bicelles with cholesteryl chloroformate-arginine 8-mer (CholR8). This also demonstrated the highest penetration of the drug-loaded bicelle across the hairless mouse skin. As a model drug, non-steroidal anti-inflammatory drug, meloxicam was selected. Meloxicam was incorporated into the hydrophobic domain of bicelles due to its hydrophobic property. Considering these results, bicelle induced with peptides exhibits useful and promising characteristics and behaviors, shaping an effective strategy for future transdermal drug delivery applications. [ABSTRACT FROM AUTHOR]

We have constructed the phase diagrams in water of two commercial additives for coatings consisting of polyether‐modified polydimethylsiloxanes. These aqueous systems form a liquid crystal mesophase (LC) at copolymer concentrations higher than 60 wt%. At low copolymer concentrations, this LC coexists with a diluted aqueous phase. Small angle x‐ray scattering (SAXS) measurements and polarized optical microscope observations indicate that the structure of the mesophase is lamellar, with an interlayer spacing that increases linearly with the concentration of water in the system. The lamellar liquid crystals display temperature‐dependent viscoelastic behavior, with the copolymer with longer spacing showing a much lower elastic modulus. Since one of the copolymer has terminal acryl groups, its lamellar phase can be crosslinked to produce gelled liquid crystals. Other cross‐linked self‐assembled structures, such as bicontinuous microemulsions, are envisaged. [ABSTRACT FROM AUTHOR]

The production of high-performance carbon fibers relies heavily on the structural transformations of polyacrylonitrile (PAN) fiber during processing. In this article differential scanning calorimetry (DSC), synchrotron small-angle X-ray scattering (SAXS), and synchrotron wide-angle X-ray diffraction (WAXD) were used to study the changes of the thermal properties, voids and crystal structure of the PAN precursor fibers on industrial lines during the continuous processing stages, i.e., after the treatment in the coagulation bath, after stretching in boiling water and after stretching in high-temperature steam. The findings of this study suggest that after boiling water stretching the molecular chain motion of the PAN precursor fiber weaken, resulting in the expansion of the voids. After high-temperature steam stretching the voids became elliptical and oriented in the stretching direction. Although the boiling water stretching process partially damaged the (100) crystal planes of the PAN precursor fibers, it does not hinder their overall crystalline structure. The high stretching ratio primarily affected the orientation of the molecular chains. This orientation, even in the context of partial crystal plane disruption, further promoted the crystallization of the (100) crystal planes in the fibers. These experiments explored the correlation between the processing technology and fiber structure transformation of PAN-based carbon fibers, resulting in producing a guide for the preparation of high-performance carbon fibers with fewer defects. [ABSTRACT FROM AUTHOR]

This study reports the pair distribution function (PDF) analysis of combined wide‐ and small‐angle X‐ray scattering (WAXS/SAXS) profiles of poly(styrene sulfonic acid) (PSSA) grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes (ETFE‐PEMs) within a wide grafting degree (GD) of 0%–117%. The PDF analysis of WAXS profiles (from Cu‐Kα1 radiation) provides a measure in size of the crystallite domains (5.1–8.7 nm). The extension of the PDF analysis for only SAXS profiles shows the distances of crystallite layers of 25.1–32 nm. In particular, SAXS‐PDF analysis is effective in showing the existence of newly generated graft domains with distances ≈60–64 nm, which can not be determined previously by the conventional SAXS analysis. The high similarity in local and higher‐order structures observed for polystyrene grafted ETFE films and ETFE‐PEMs suggests that the hierarchical structures including the spatial arrangement of large amorphous contents in the membranes can be determined at the graft polymerization step. Note that the presence of newly generated PSSA graft domains at large dimension can explain well the comparable or higher proton conductivity of ETFE‐PEMs as compared with commercial Nafion membrane. [ABSTRACT FROM AUTHOR]

The distribution of nanosilver in composite materials with two different matrices is related to the selection of antibacterial masterbatches, which has a profound impact on the antibacterial effectiveness of the composite materials. This study utilized ethylene‐vinyl acetate (EVA) and polypropylene (PP) as base materials to fabricate two types of nanosilver composite materials (C1‐EVA/PP and C2‐EVA/PPP) employing varying methods of antimicrobial masterbatches incorporation. Additionally, EVA‐Ag and PP‐Ag nanosilver composite materials were fabricated via melt blending, along with corresponding neat materials and blends (EVA, PP, and C0‐EVA/PP) for comparison. The study results indicate that the addition of nanosilver did not affect the functional groups of either the neat materials and the EVA/PP blends. SEM analysis revealed that nanosilver was dispersed unevenly in the C1‐EVA/PP substrate, while it was more uniformly distributed in the C2‐EVA/PP substrate. In the antibacterial test, the antibacterial rate of C2‐EVA/PP was higher than that of C1‐EVA/PP (56.0% vs. 40.0%). However, all silver‐containing composite materials did not exhibit antibacterial properties in the agar diffusion test. Additionally, nanosilver exhibited an induced crystallization effect on the PP phase of the C2‐EVA/PP composite material, increasing its Tc2 by 0.8°C. Compared with pure PP, the long period of PP‐Ag increased by 0.7 nm, and its impact resistance improved by 13.8%. By comparison, the long period of EVA‐Ag composite materials increased by only 0.2 nm compared to pure EVA. Both C1‐EVA/PP and C2‐EVA/PP composite materials showed 0.3 nm increase in long period compared to C0‐EVA/PP, with their impact resistance improving by 3.1% and 10.3%, respectively, compared to C0‐EVA/PP. The introduction of nanosilver increased the storage modulus, loss modulus, and apparent viscosity of EVA/PP blends. Optical performance analysis shows that nanosilver increases the internal haze of C1‐EVA/PPP by 60% while reducing the transmittance by 0.3%. The effect of nanosilver on the optical properties of C2‐EVA/PPP composites is relatively small. Therefore, this study provides theoretical guidance for the selection of processing methods for dual‐phase antibacterial materials. Highlights: Different antibacterial masterbatch impacts silver distribution in composites.The addition of nanosilver can improve the impact performance of materials.Two process methods were used to prepare low‐silver content composite materials.The antibacterial rate of C2‐EVA/PP is higher than C1‐EVA/PP (56% vs. 40%).This study guides the processing methods for dual‐phase antibacterial materials. [ABSTRACT FROM AUTHOR]

Most nonconventional luminogens enjoy good water solubility and biocompatibility, showing unique application prospects in fields like biological imaging. Although clustering‐triggered emission (CTE) mechanisms have been proposed to explain such emissions, it has not been thoroughly elucidated, which limits their development and application. Herein, the photoluminescence properties of polyacrylamide prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization aqueous solution are utilized to further investigate the effects of changes in concentration, in order to elucidate the emission mechanism through transmission electron microscopy (TEM), small angle X‐ray scattering (SAXS) and theoretical calculation. The results showed that the size distribution, morphology, and distance between the polymer clusters formed in the water solution are successfully correlated with the cluster emission centers. The emission mechanism of nonconventional luminogens solutions is more clearly and intuitively elucidated, which has a promoting effect on the emission and application of this field. It provides a strategy a strategy to clarify the CTE mechanism of nonconventional luminogens solution more clearly. [ABSTRACT FROM AUTHOR]

This research aimed to develop neomycin sulfate-loaded transferosomal vesicles designed for efficient vaginal delivery. The study employed a modified handshaking technique to enhance drug permeability through the vaginal mucosa, utilizing various surfactants at three concentrations while maintaining constant drug concentration. Neomycin sulphate transferosomes were made using a modified hand shaking method and seven different edge activators, which included Brij35, sodium deoxycholate cremophor EL, tween80, span80, and tween20, at three different concentrations of phosphotidylcholine. These formulations were then tested for surface characteristics (scanning electron microscopy and transmission electron microscopy), particle size distribution, zeta potential, differential scanning calorimetry, X-ray diffraction, Fourier transform infrared, small angle X-ray scattering, ex vivo permeation studies, and confocal scanning laser microscopy studies. The phospholipid layer's intercalatable surfactant, span80, was used in the formulation process to produce a stable vesicular formulation. The findings showed that the transferosomes loaded with neomycin sulfate were stable, uniformly distributed, and had a particle size of 152.8 nm, a polydispersity index value of 0.368, and a zeta potential of 5.04±0.2 mV. Furthermore, the efficiency of entrapment was 89.87 %. The transferosomes high deformability-a deformability index of 31.8 was validated by the lipid extrusion test. Neomycin sulfate was successfully loaded into vesicles, as demonstrated by additional analysis using differential scanning calorimetry, X-diffract gram patterns, and small angle X-ray scattering studies. These findings suggested that the vesicles were amorphous and that unilamellar vesicles had formed. In vitro permeation investigations on sheep vaginal tissue at pH 4.4 citrate buffer indicated promising results for the improved formulation, including a flux value of 0.789 mg/h/cm2, a permeability coefficient of 0.0956, a short lag time of 0.434 h, and a 12-fold enhancement ratio compared to pure medication. Confocal laser scanning microscopy investigations validated the vesicles' deformability and improved permeability. In conclusion, neomycin sulfate-loaded transferosomes showed great promise as a drug delivery technology for vaginal applications. The proposed vesicular formulation demonstrated superior properties such as stability, deformability, and increased permeability, making it a promising carrier with fewer side effects and the possibility for easy scale-up and production at lower medication doses. [ABSTRACT FROM AUTHOR]

The function of cellobiose dehydrogenase (CDH) in biosensors, biofuel cells, and as a physiological redox partner of lytic polysaccharide monooxygenase (LPMO) is based on its role as an electron donor. Before donating electrons to LPMO or electrodes, an interdomain electron transfer from the catalytic FAD-containing dehydrogenase domain to the electron shuttling cytochrome domain of CDH is required. This study investigates the role of two crucial amino acids located at the dehydrogenase domain on domain interaction and interdomain electron transfer by structure-based engineering. The electron transfer kinetics of wild-type Myriococcum thermophilum CDH and its variants M309A, R698S, and M309A/R698S were analyzed by stopped-flow spectrophotometry and structural effects were studied by small-angle X-ray scattering. The data show that R698 is essential to pull the cytochrome domain close to the dehydrogenase domain and orient the heme propionate group towards the FAD, while M309 is an integral part of the electron transfer pathway - its mutation reducing the interdomain electron transfer 10-fold. Structural models and molecular dynamics simulations pinpoint the action of these two residues on the domain interaction and interdomain electron transfer.

The interdomain electron transfer (IET) between the catalytic flavodehydrogenase domain and the electron-transferring cytochrome domain of cellobiose dehydrogenase (CDH) plays an essential role in biocatalysis, biosensors and biofuel cells, as well as in its natural function as an auxiliary enzyme of lytic polysaccharide monooxygenase. We investigated the mobility of the cytochrome and dehydrogenase domains of CDH, which is hypothesised to limit IET in solution by small angle X-ray scattering (SAXS). CDH from Myriococcum thermophilum (syn. Crassicarpon hotsonii, syn. Thermothelomyces myriococcoides) was probed by SAXS to study the CDH mobility at different pH and in the presence of divalent cations. By comparison of the experimental SAXS data, using pair-distance distribution functions and Kratky plots, we show an increase in CDH mobility at higher pH, indicating alterations of domain mobility. To further visualise CDH movement in solution, we performed SAXS-based multistate modelling. Glycan structures present on CDH partially masked the resulting SAXS shapes, we diminished these effects by deglycosylation and studied the effect of glycoforms by modelling. The modelling shows that with increasing pH, the cytochrome domain adopts a more flexible state with significant separation from the dehydrogenase domain. On the contrary, the presence of calcium ions decreases the mobility of the cytochrome domain. Experimental SAXS data, multistate modelling and previously reported kinetic data show how pH and divalent ions impact the closed state necessary for the IET governed by the movement of the CDH cytochrome domain.

Background F-keratin forms an evolutionary conserved nanocomposite which allows birds to fly. Structural models for F-keratin are all based on the pioneering X-ray diffraction studies on seagull F-keratin, first published in 1932, confirmed for other species and refined over the years. There is, however, no experimental proof because native F-keratin does not form a perfect molecular crystal as required for structure determination. Methods Peacock’s tail feathers were systematically re-investigated by taking diffraction patterns at different rotation angles. Using the recently developed AlphaFold algorithm, a collection of 3D models of arbitrarily truncated and multiplied Pavo cristatus F-keratin sequences was created. The shape, dimensions, density and interfacial exposure of functionally relevant amino acid side chains of the calculated 3D building blocks were used as the initial selection criteria for filamentous F-keratin precursors. Full reproducibility of in silico folding and agreement with previous results from mechanical testing, biochemical analyses and SAXS experiments was mandatory for suggesting the tentative structure for the novel F-keratin repeating unit. Results The filament of the F-keratin polymer is an alternating arrangement of two units called 'N-block' and 'C-block': Four strands AA 1–52 form a disulfide-stabilized twisted parallelepiped, with 89° internal rotation within eight levels of β-sandwiches. Four strands AA 81–100 form a two-level “ β-sandwich” in which aromatic residues provide resilience, like vertebral discs in a spinal column. The pitch of an N+C-block octamer is 10 nm. Solidification may involve 'C-blocks' to temporarily mold into 'C-wedges' of 18° tilt, which align F-keratin into laterally amorphous fiber-reinforced composites of 9.5 nm axial periodicity. This experimentally significant distance corresponds to the fully stretched AA 53–80 matrix segment. The deformed “spinal column” unwinds under compression when F-keratin filaments perfectly align horizontally into stacked sheets in the solid state. Conclusions At present, the tentative structure presented here is without alternatives.

Using a solution‐mixing method, this research aimed to fabricate high‐density polyethylene (HDPE)/ultra‐high molecular weight polyethylene (UHMWPE) composite materials with uniform dispersion. By incorporating a small quantity of UHMWPE as a nucleating agent, additional contact points were introduced to enhance the crystallization rate of the HDPE matrix. Thermal stretching experiments were conducted on composite systems with varying UHMWPE contents and molecular weight additions at different temperatures. Elevating the stretching temperature was found to decrease the yield strain and yield strength, extend the stage of tensile plastic deformation, and diminish the overall mechanical properties of the composite material. Notably, stretching at temperatures ranging from 90 to 110°C accentuated the development of internal crystal orientation structures. Under low strain conditions, crystal slip was observed to be concentrated, with single crystals undergoing continuous stretching and breaking, resulting in a decrease in the long period. Conversely, at high strains, the induced formation of oriented lamellar structures was observed. Highlights: Prepared HDPE/UHMWPE blends by UHMWPE with varying molecular weights.Analyzed the alterations in the HDPE/UHMWPE blends' internal crystal structure.Influence of UHMWPE addition, temperature on the evolution of crystal structure. [ABSTRACT FROM AUTHOR]

Rieske oxygenases (ROs) are a diverse metalloenzyme class with growing potential in bioconversion and synthetic applications. We postulated that ROs are nonetheless underutilized because they are unstable. Terephthalate dioxygenase (TPADO PDB ID 7Q05) is a structurally characterized heterohexameric α3β3 RO that, with its cognate reductase (TPARED), catalyzes the first intracellular step of bacterial polyethylene terephthalate plastic bioconversion. Here, we showed that the heterologously expressed TPADO/TPARED system exhibits only ~300 total turnovers at its optimal pH and temperature. We investigated the thermal stability of the system and the unfolding pathway of TPADO through a combination of biochemical and biophysical approaches. The system's activity is thermally limited by a melting temperature (Tm) of 39.9°C for the monomeric TPARED, while the independent Tm of TPADO is 50.8°C. Differential scanning calorimetry revealed a two‐step thermal decomposition pathway for TPADO with Tm values of 47.6 and 58.0°C (ΔH = 210 and 509 kcal mol−1, respectively) for each step. Temperature‐dependent small‐angle x‐ray scattering and dynamic light scattering both detected heat‐induced dissociation of TPADO subunits at 53.8°C, followed by higher‐temperature loss of tertiary structure that coincided with protein aggregation. The computed enthalpies of dissociation for the monomer interfaces were most congruent with a decomposition pathway initiated by β‐β interface dissociation, a pattern predicted to be widespread in ROs. As a strategy for enhancing TPADO stability, we propose prioritizing the re‐engineering of the β subunit interfaces, with subsequent targeted improvements of the subunits. [ABSTRACT FROM AUTHOR]

We introduce an innovative theoretical framework tailored for the analysis of Pair Distribution Function (PDF) data derived from Small-Angle X-ray Scattering (SAXS) measurements of core-shell micelles. The new approach involves the exploitation of the first derivative of the PDF and the derivation of analytical equations to solve the core-shell micelle structure under the hypothesis of a spheroidal shape. These analytical equations enable us to determine the micelle's aggregation number, degree of ellipticity, and contrast in electron density between the core-shell and shell-buffer regions after having determined the whole micelle size and its shell size from the analysis of the first derivative of the PDF. We have formulated an overdetermined system of analytical equations based on the unknowns that characterize the micelle structure. This allows us to establish a Figure of Merit, which is utilized to identify the most reliable solution within the system of equations. [ABSTRACT FROM AUTHOR]

The use of block copolymers to compatibilize immiscible plastics is an important strategy for upcycling municipal plastic wastes. Multiblock copolymers (MBCPs) have been proven to be more effective compatibilizers than di- and tri-block copolymers. Herein, we probe the interface structure of an effective multiblock copolymer compatibilizer and compare that with an ineffective triblock copolymer (TBCP). The interface activity of the compatibilizers is understood through a combination of small-angle neutron and x-ray scatterings (SANS and SAXS), by using deuterated homopolymer matrix and protonated compatibilizers. SANS analysis suggests that the MBCP forms a thicker interface layer (7-9 nm) than the TBCP (0-4 nm). In addition, SANS data seems to point to a stronger tendency for the MBCP to locate at the interface. Both factors contribute to its effectiveness at compatibilizing immiscible homopolymers. [ABSTRACT FROM AUTHOR]

Based on the binary system of ionic surfactant C14TAB and water, the optical properties and phase behavior of them including isotropy/anisotropy, birefringence, and optical texture are studied by polarized light microscopy and visual observation. The structure and parameters of the lyotropic liquid crystal phase are characterized by small angle X-ray scattering (SAXS), and the binary phase diagram is constructed. This experiment expands the research system, reduces the experimental cost, and improves the experimental accuracy based on the original comprehensive chemistry experiment. It is helpful to understand the microstructure and properties of lyotropic liquid crystals; master the principles and methods of characterization techniques; stimulate the interests of students in physical chemistry. Further, it contributes to help students expand their scientific logic and improve their experimental skills. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, the nanostructures of metal alloy Ti6Al4V implants produced by the selective laser melting (SLM) technique were examined using the SAXS method, depending on the annealing temperature, and the relationship between these nanostructures and bioactivity was examined for the first time. Annealing process in this technique increases the durability and makes alloys more suitable for processing. In this study, in order to understand the effect of annealing temperature on the nanostructure, five identical samples without annealing and five identical samples annealed at different temperatures (T = 780, 840, 1040 °C) were examined and compared with each other structurally. Beside of nanoscopic SAXS analyses, SEM imaging and macrophotography techniques were also used as supporting evidence. Additionally, antimicrobial test was applied to determine the antimicrobial properties of the samples, too. As a result, the best annealing temperature (840 °C) was determined to prepare implant materials with uniform and homogeneously distributed nanospherical (Rg = 13.4 ± 0.3 nm radius) formations. The morphologies, sizes, radial electron densities, and distance distributions of the nanoaggregations in the implant content, determined as a result of SAXS data evaluations, constituted nanoscopic findings. It was also shown that this nanostructured implant has an antibiofilm effect against S.aureus. [ABSTRACT FROM AUTHOR]

[Display omitted] The self-assembly structures and phase behaviour of phospholipids in protic ionic liquids (ILs) depend on intermolecular forces that can be controlled through changes in the size, polarity, and H-bond capacity of the solvent. The structure and temperature stability of the self-assembled phases formed by four phospholipids in three ILs was determined by a combination of small- and wide-angle X-ray scattering (SAXS and WAXS) and small-angle neutron scattering (SANS). The phospholipids have identical phosphocholine head groups but different alkyl tail lengths and saturations (DOPC, POPC, DPPC and DSPC), while the ILs' amphiphilicity, H–bond network density and polarity are varied between propylammonium nitrate (PAN) to ethylammonium nitrate (EAN) to ethanolammonium nitrate (EtAN). The observed structures and phase behaviour of the lipids becomes more surfactant–like with decreasing average solvent polarity, H-bond network density and surface tension. In PAN, all the investigated phospholipids behave like surfactants in water. In EAN they exhibit anomalous phase sequences and unexpected transitions as a function of temperature, while EtAN supports structures that share characteristics with water and EAN. Structures formed are also sensitive to proximity to the lipid chain melting temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] Enveloped viruses are pivotal in causing various illnesses, including influenza and COVID-19. The antimicrobial peptide LL-37, a critical part of the human innate immune system, exhibits potential as an antiviral agent capable of thwarting these viral threats. Its mode of action involves versatile and non-specific interactions that culminate in dismantling the viral envelope, ultimately rendering the viruses inert. However, the exact mechanism of action is not yet understood. Here, the mechanism of LL-37 triggered changes in the structure and function of an enveloped virus is investigated. The bacteriophage "Phi6" is used as a surrogate for pathogenic enveloped viruses. Small angle X-ray and neutron scattering combined with light scattering techniques demonstrate that LL-37 actively integrates into the virus's lipid envelope. LL-37 addition to Phi6 leads to curvature modification in the lipid bilayer, ultimately separating the envelope from the nucleocapsid. Additional biological assays confirm the loss of virus infectivity in the presence of LL-37, which coincides with the structural transformations. The results provide a fundamental understanding of the structure-activity relationship related to enveloped viruses. The knowledge of peptide-virus interactions can guide the design of future peptide-based antiviral drugs and therapies. [ABSTRACT FROM AUTHOR]

RNA molecules serve a wide range of functions that are closely linked to their structures. The basic structural units of RNA consist of single- and double-stranded regions. In order to carry out advanced functions such as catalysis and ligand binding, certain types of RNAs can adopt higher-order structures. The analysis of RNA structures has progressed alongside advancements in structural biology techniques, but it comes with its own set of challenges and corresponding solutions. In this review, we will discuss recent advances in RNA structure analysis techniques, including structural probing methods, X-ray crystallography, nuclear magnetic resonance, cryo-electron microscopy, and small-angle X-ray scattering. Often, a combination of multiple techniques is employed for the integrated analysis of RNA structures. We also survey important RNA structures that have been recently determined using various techniques.

Annexin A11 (ANXA11) is a calcium-dependent phospholipid-binding protein belonging to the annexin protein family and implicated in the neurodegenerative amyotrophic lateral sclerosis. Structurally, ANXA11 contains a conserved calcium-binding C-terminal domain common to all annexins and a putative intrinsically unfolded N-terminus specific for ANXA11. Little is known about the structure and functions of this region of the protein. By analogy with annexin A1, it was suggested that residues 38 to 59 within the ANXA11 N-terminus could form a helical region that would be involved in interactions. Interestingly, this region contains residues that, when mutated, may lead to clinical manifestations. In the present study, we have studied the structural features of the full-length protein with special attention to the N-terminal region using a combination of biophysical techniques which include nuclear magnetic resonance and small angle X-ray scattering. We show that the N-terminus is intrinsically disordered and that the overall features of the protein are not markedly affected by the presence of calcium. We also analyzed the 38–59 helix hypothesis using synthetic peptides spanning both the wild-type sequence and clinically relevant mutations. We show that the peptides have a remarkable character typical of a native helix and that mutations do not alter the behaviour suggesting that they are required for interactions rather than being structurally important. Our work paves the way to a more thorough understanding of the ANXA11 functions.

In this article, chemical structure and conformation in an aqueous solution of a new sulfated polysaccharide, PCL, extracted from green seaweed Chaetomorpha linum were elucidated by SEC-MALL, IR, NMR and SAXS. The results indicated that the obtained polysaccharide is a sulfated arabinogalactan with a molecular weight of 223 kDa, and is mainly composed of →3,6)-α-D-Galp4S→ and →2)-α-L-Araf→ connecting together through 1→3 glycoside linkages. It has a broken rod-like conformation in solution with Rgc estimated as 0.43 nm from SAXS measurements. The polysaccharide exhibited a notable anticoagulant activity measured by the assays of activated partial thromboplastintime, thrombintime and prothrombine time as well as a significant cytotoxic activity against hepatocellular, human breast cancer, and cervical cancer cell lines. [ABSTRACT FROM AUTHOR]

[Display omitted] Understanding protein behaviour is crucial for developing functional solvent systems. Ionic liquids (ILs) are designer salts with versatile ion combinations, where some suppress unfavourable protein behaviour. This work utilizes small angle X-ray scattering (SAXS) to investigate the size and shape changes of model protein hen egg white lysozyme (HEWL) in 137 IL and salt solutions. Guinier, Kratky, and pair distance distribution analysis were used to evaluate the protein size, shape, and aggregation changes in these solvents. At low IL and salt concentration (1 mol%), HEWL remained monodispersed and globular. Most ILs increased HEWL size compared to buffer, while the nitrate and mesylate anions induced the most significant size increases. IL cation branching, hydroxyl groups, and longer alkyl chains counteracted this size increase. Common salts exhibited specific ion effects, while the IL effect varied with concentration due to complex ion-pairing. Protein aggregation and unfolding occurred at 10 mol% IL, altering the protein shape, especially for ILs with multiple alkyl chains on the cation, or with a mesylate/nitrate anion. This study highlights the usefulness of adopting a high-throughput SAXS strategy for understanding IL effects on protein behaviour and provides insights on controlling protein aggregation and unfolding with ILs. [ABSTRACT FROM AUTHOR]

Recently, we reported a series of reversibly interlocked polymer networks (RILNs), whose mechanical robustness and functionalities improvement was believed to be derived from topological interlocking of two sub-networks, although the direct evidence for the deduction is still lacking. Herein, a specially-designed RILNs system, in which the inter-component hydrogen bonds can be shielded as needed, was prepared and used to study the micro-structures of RILNs, aiming to verify the existence of mechanical interlocking in RILNs. By changing the pH of the swelling solvent, the effect exerted by the inter-component non-covalent bonds was eliminated, so detailed information of the networks structure was exposed. The small angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) results indicated that swelling-induced structural evolution of the two sub-networks mutually affected each other, even when the inter-component hydrogen bonds were absent, proving the presence of topological interlocking. The findings may help to draw a more accurate physical image and reveal the detailed structure-property relationship of RILNs. [ABSTRACT FROM AUTHOR]

Diesel Oxidation Catalyst (DOC) is the most important and advanced part of the after-treatment technology route. After the exhaust passes through DOC, CO, and HC will be significantly reduced, while particles are mainly captured by the Diesel Particulate Filter (DPF) device behind. In order to further investigate the effect of DOC on the nano-structure characteristics of diesel emission particles. The particles before and after DOC of 186FA diesel engine at 2700 r/min, 100% load, and 3600 r/min, 100% load are collected. The nano-structure characteristics of particles are investigated using field emission transmission electron microscopy (FETEM) combined with small angle X-ray scattering radiation technique (SAXS). Based on FETEM and SAXS analysis of particles, a nano-scale particle spatial structure model including particle size, pores, and visual boundary layer is proposed. The results show that the average radius, interface layer thickness, and fractal dimension of the particles are reduced after the DOC. In contrast, the specific surface area of the particles is increased after the DOC. At 3600 r/min 100% load, the average radius is reduced from 23.3 to 21.5 nm, accounting for 7.8%. Interface layer thickness is reduced from 13.3 to 12.9 nm. The specific surface area of the particles is increased from 0.146 to 0.166 m² /mm³ . The research results provide a theoretical basis for the regeneration and oxidation of particles in DPF. [ABSTRACT FROM AUTHOR]

[Display omitted] In the last 20 years, it has been demonstrated that oppositely charged polyelectrolyte-surfactant (PE-S) mixtures are prone to forming kinetically arrested non-equilibrium aggregates, which are present in the prepared mixtures from rather low surfactant-to-polymer-repeat-unit ratios. Practically, this means that the PE-S mixtures used for the structural investigations of the formed PE-S complexes are typically a mixture of the primary PE-S complexes and large non-equilibrium aggregates of close to charge-neutral complexes. In this work, we present a unique approach that allows the preparation of PE-S mixtures in the equilibrium one-phase region (surfactant binding β , is typically below 80%) without forming non-equilibrium aggregates. We used this method to prepare equilibrium, non-aggregated complexes of sodium poly(styrene sulfonate) (NaPSS, M w = 17 kDa) and dodecyltrimethylammonium bromide (DTAB) (β = 10 – 70%) both in water and in an inert electrolyte (100 mM NaCl). The evolution of the complex structure was monitored by small-angle X-ray scattering (SAXS) as a function of increasing surfactant binding (β), and the measured scattering data were fitted by suitable structural models on an absolute scale where concentrations, compositions, and scattering contrasts calculated from molecular properties are used as restraints. We could show that at low binding (β < 30%), the system is a mixture of bare polyelectrolyte coils and NaPSS-DTAB complexes containing a closed surfactant associates of low aggregation number wrapped by the polyelectrolyte chain. Once all polymer chains are occupied by a micelle-like surfactant aggregate, the aggregation number increases linearly with increasing surfactant chemical potential. Using the structural insight provided by the SAXS measurements, we could fit the experimental binding isotherm data with a physically coherent, simple thermodynamic model. Finally, we also compared the stoichiometric NaPSS-DTAB precipitate's structure with the equilibrium complexes' structure. [ABSTRACT FROM AUTHOR]

In an in‐depth study of the mechanism of cation release from carboxymethyl cellulose hydrogels synthesized through Schiff base reaction, we analyze the differences in the release kinetics of potassium, calcium, and iron cations with Peleg model at pH values of pH 3.5 and pH 8.5 using ICP‐OES (inductively coupled plasma optical emission spectroscopy) technique. [ABSTRACT FROM AUTHOR]

Guanylate‐binding proteins (GBPs) are essential interferon‐γ‐activated large GTPases that play a crucial role in host defense against intracellular bacteria and parasites. While their protective functions rely on protein polymerization, our understanding of the structural intricacies of these multimerized states remains limited. To bridge this knowledge gap, we present dimer models for human GBP1 (hGBP1) and murine GBP2 and 7 (mGBP2 and mGBP7) using an integrative approach, incorporating the crystal structure of hGBP1's GTPase domain dimer, crosslinking mass spectrometry, small‐angle X‐ray scattering, protein–protein docking, and molecular dynamics simulations. Our investigation begins by comparing the protein dynamics of hGBP1, mGBP2, and mGBP7. We observe that the M/E domain in all three proteins exhibits significant mobility and hinge motion, with mGBP7 displaying a slightly less pronounced motion but greater flexibility in its GTPase domain. These dynamic distinctions can be attributed to variations in the sequences of mGBP7 and hGBP1/mGBP2, resulting in different dimerization modes. Unlike hGBP1 and its close ortholog mGBP2, which exclusively dimerize through their GTPase domains, we find that mGBP7 exhibits three equally probable alternative dimer structures. The GTPase domain of mGBP7 is only partially involved in its dimerization, primarily due to an accumulation of negative charge, allowing mGBP7 to dimerize independently of GTP. Instead, mGBP7 exhibits a strong tendency to dimerize in an antiparallel arrangement across its stalks. The results of this work go beyond the sequence–structure–function relationship, as the sequence differences in mGBP7 and mGBP2/hGBP1 do not lead to different structures, but to different protein dynamics and dimerization. The distinct GBP dimer structures are expected to encode specific functions crucial for disrupting pathogen membranes. [ABSTRACT FROM AUTHOR]

The alignment of anisotropic nanoparticles in flow has been used for a range of applications such as the preparation of strong fibres and the assembly of in‐plane aligned 1D‐nanoobjects that are used for electronic devices, sensors, energy and biological application. Important is also the flow behaviour of nanoparticles that were designed for nanomedical applications such as drug delivery. It is widely observed that non‐spherical nanoparticles have longer circulation times and a more favourable biodistribution. To be able to understand this behaviour, researchers have turned to analyzing the flow of non‐spherical nanoparticles in the blood stream. In this review, an overview of microfluidic techniques that are used to monitor the alignment of anisotropic nanoparticles in solution will be provided, which includes analysis by small angle X‐ray scattering (SAXS) and polarized light microscopy. The flow of these nanoparticles in blood is then discussed as the presence of red blood cells causes margination of some nanoparticles. Using fluorescence microscopy, the extent of margination can be identified, which coincides with the ability of nanoparticles to adhere to the cells grown along the wall. While these studies are mainly carried out in vitro using blood, initial investigations in vivo were able to confirm the unusual flow of anisotropic nanoparticles. [ABSTRACT FROM AUTHOR]

Tyrosyl DNA phosphodiesterase 1 (TDP1) and DNA Ligase IIIα (LigIIIα) are key enzymes in single-strand break (SSB) repair. TDP1 removes 3'-tyrosine residues remaining after degradation of DNA topoisomerase (TOP) 1 cleavage complexes trapped by either DNA lesions or TOP1 inhibitors. It is not known how TDP1 is linked to subsequent processing and LigIIIα-catalyzed joining of the SSB. Here we define a direct interaction between the TDP1 catalytic domain and the LigIII DNA-binding domain (DBD) regulated by conformational changes in the unstructured TDP1 N-terminal region induced by phosphorylation and/or alterations in amino acid sequence. Full-length and N-terminally truncated TDP1 are more effective at correcting SSB repair defects in TDP1 null cells compared with full-length TDP1 with amino acid substitutions of an N-terminal serine residue phosphorylated in response to DNA damage. TDP1 forms a stable complex with LigIII170-755, as well as full-length LigIIIα alone or in complex with the DNA repair scaffold protein XRCC1. Small-angle X-ray scattering and negative stain electron microscopy combined with mapping of the interacting regions identified a TDP1/LigIIIα compact dimer of heterodimers in which the two LigIII catalytic cores are positioned in the center, whereas the two TDP1 molecules are located at the edges of the core complex flanked by highly flexible regions that can interact with other repair proteins and SSBs. As TDP1and LigIIIα together repair adducts caused by TOP1 cancer chemotherapy inhibitors, the defined interaction architecture and regulation of this enzyme complex provide insights into a key repair pathway in nonmalignant and cancer cells.

Bacteria have evolved elaborate mechanisms to thrive in stressful environments. F-like plasmids in gram-negative bacteria encode for a multi-protein Type IV Secretion System (T4SSF) that is functional for bacterial proliferation and adaptation through the process of conjugation. The periplasmic protein TrbB is believed to have a stabilizing chaperone role in the T4SSF assembly, with TrbB exhibiting disulfide isomerase (DI) activity. In the current report, we demonstrate that the deletion of the disordered N-terminus of TrbBWT, resulting in a truncation construct TrbB37-161, does not affect its catalytic in vitro activity compared to the wild-type protein (p = 0.76). Residues W37–K161, which include the active thioredoxin motif, are sufficient for DI activity. The N-terminus of TrbBWT is disordered as indicated by a structural model of GST-TrbBWT based on ColabFold-AlphaFold2 and Small Angle X-Ray Scattering data and 1H–15N Heteronuclear Single Quantum Correlation (HSQC) spectroscopy of the untagged protein. This disordered region likely contributes to the protein's dynamicity; removal of this region results in a more stable protein based on 1H–15N HSQC and Circular Dichroism Spectroscopies. Lastly, size exclusion chromatography analysis of TrbBWT in the presence of TraW, a T4SSF assembly protein predicted to interact with TrbBWT, does not support the inference of a stable complex forming in vitro. This work advances our understanding of TrbB's structure and function, explores the role of structural disorder in protein dynamics in the context of a T4SSF accessory protein, and highlights the importance of redox-assisted protein folding in the T4SSF.

Abstract The alignment of anisotropic nanoparticles in flow has been used for a range of applications such as the preparation of strong fibres and the assembly of in‐plane aligned 1D‐nanoobjects that are used for electronic devices, sensors, energy and biological application. Important is also the flow behaviour of nanoparticles that were designed for nanomedical applications such as drug delivery. It is widely observed that non‐spherical nanoparticles have longer circulation times and a more favourable biodistribution. To be able to understand this behaviour, researchers have turned to analyzing the flow of non‐spherical nanoparticles in the blood stream. In this review, an overview of microfluidic techniques that are used to monitor the alignment of anisotropic nanoparticles in solution will be provided, which includes analysis by small angle X‐ray scattering (SAXS) and polarized light microscopy. The flow of these nanoparticles in blood is then discussed as the presence of red blood cells causes margination of some nanoparticles. Using fluorescence microscopy, the extent of margination can be identified, which coincides with the ability of nanoparticles to adhere to the cells grown along the wall. While these studies are mainly carried out in vitro using blood, initial investigations in vivo were able to confirm the unusual flow of anisotropic nanoparticles.

[Display omitted] The iridescent optical properties of films made of cellulose nanocrystals (CNC) are controlled by the pitch and range of the chiral nematic structures. These are further tuned with the addition of electrolyte. Electrolyte type, valency and concentration were varied. The bulk CNC suspension properties were investigated by combining rheology, polarised optical photography and microscopy, while the spacing between crystals was determined using SAXS. The addition of electrolyte to a CNC suspension containing chiral nematic structures first causes the nematic pitch to increase indicating the suspension has a weaker structure. Further increases in electrolyte concentration cause aggregation and complete breakdown of the chiral nematic structures. The univalent species cause larger changes to the chiral nematic structure with the onset and magnitude of structure breakdown occurring at lower ionic strengths compared with the divalent species. Cation size influences the chiral nematic structure with the order of influence being K+ > Na+ ≈ Ca2+ > Mg2+, which corresponds from the largest to smallest cation. This work demonstrates that both ion valency, concentration and species play a significant role in controlling the chiral nematic structures of CNC suspensions and will be a vital step in the development of CNC liquid crystals, optical materials and sensors. [ABSTRACT FROM AUTHOR]

Calcific degeneration is the most frequent type of heart valve failure, with rising incidence due to the ageing population. The gold standard treatment to date is valve replacement. Unfortunately, calcification oftentimes re-occurs in bioprosthetic substitutes, with the governing processes remaining poorly understood. Here, we present a multiscale, multimodal analysis of disturbances and extensive mineralisation of the collagen network in failed bioprosthetic bovine pericardium valve explants with full histoanatomical context. In addition to highly abundant mineralized collagen fibres and fibrils, calcified micron-sized particles previously discovered in native valves were also prevalent on the aortic as well as the ventricular surface of bioprosthetic valves. The two mineral types (fibres and particles) were detectable even in early-stage mineralisation, prior to any macroscopic calcification. Based on multiscale multimodal characterisation and high-fidelity simulations, we demonstrate that mineral occurrence coincides with regions exposed to high haemodynamic and biomechanical indicators. These insights obtained by multiscale analysis of failed bioprosthetic valves serve as groundwork for the evidence-based development of more durable alternatives. Bioprosthetic valve calcification is a well-known clinically significant phenomenon, leading to valve failure. The nanoanalytical characterisation of bioprosthetic valves gives insights into the highly abundant, extensive calcification and disorganization of the collagen network and the presence of calcium phosphate particles previously reported in native cardiovascular tissues. While the collagen matrix mineralisation can be primarily attributed to a combination of chemical and mechanical alterations, the calcified particles are likely of host cellular origin. This work presents a straightforward route to mineral identification and characterization at high resolution and sensitivity, and with full histoanatomical context and correlation to hemodynamic and biomechanical indicators, hence providing design cues for improved bioprosthetic valve alternatives. [Display omitted] [ABSTRACT FROM AUTHOR]

Small‐Angle Scattering (SAS) techniques are essential tools for the characterization of catalysts before, during and after catalytic reactions. Either based on X‐Rays (SAXS) or neutrons (SANS), they provide unique structural information that helps to understand catalytic processes at the nanoscale level, allowing a rational improvement of the catalysts design. In this review, we present the key aspects involved in the use of these techniques in the catalysis field. Firstly, we introduce some of the fundamentals of the techniques and describe their main features and their impact in the catalyst design. Then, we analyze key examples of the use of SAS to study catalysts' structure through ex situ analysis, focusing on examples involving different porous materials and metallic nanoparticles. Afterwards, we discuss in situ and operando approaches for studying catalytical processes monitored using SAS. Finally, we present perspectives and challenges for the future use of SAS in the catalysis field. [ABSTRACT FROM AUTHOR]

Concentrated cellulose nanocrystal (CNC) suspensions are known to self-assemble into liquid crystalline cholesteric phase. However, the origin of this chirality transfer is still matter of discussion. In this work, we used a tailor-made biopolymer, xyloglucan (XG), at a very small molar mass (20,000 g/mol) that adsorb flat on the cellulose surface. We showed that the addition to a dispersion of CNCs at 60 g/L of XG up to 10 g/L decreased the anisotropic volume fraction, increased the cholesteric pitch, and kept constant the inter-CNC distance implying a change in the twist angle and a lower chiral strength. These results indicate that a very limited modification of CNCs on surface can induce important variation of the cholesteric order. Above 10 g/L XG, XG-covered CNCs decreased the cholesteric pitch and preferentially concentrated in the isotropic phase, decreasing the global cholesteric liquid crystalline (CLC) order. [ABSTRACT FROM AUTHOR]

[Display omitted] The forces that govern lipid self-assembly ionic liquids are similar to water, but their different balance can result in unexpected behaviour. The self-assembly behaviour and phase equilibria of two phospholipids, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), in the most common protic ionic liquid, ethylammonium nitrate (EAN) have been investigated as function of composition and temperature by small- and wide-angle X-ray scattering (SAXS/WAXS) and small-angle neutron scattering (SANS). Both lipids form unusual self-assembly structures and show complex and unexpected phase behaviour unlike that seen in water; DSPC undergoes a gel L β to crystalline L c phase transition on warming, while POPC forms worm-like micelles L 1 upon dilution. This surprising phase behaviour is attributed to the large size of the EAN ions that solvate the lipid headgroup compared to water changing amphiphile packing. Weaker H-bonding between EAN and lipid headgroups also contributes. These results provide new insight for the design of lipid based nanostructured materials in ionic liquids with atypical properties. [ABSTRACT FROM AUTHOR]

Human aromatic amino acid decarboxylase (AADC) is a pyridoxal 5′‐phosphate‐dependent enzyme responsible for the biosynthesis of dopamine and serotonin, essential neurotransmitters involved in motor and cognitive abilities. Mutations in its gene lead to AADC deficiency, a monogenic rare neurometabolic childhood parkinsonism characterized by severe motor and neurodevelopmental symptoms. Here, for the first time, we solved the crystal structure of human holoAADC in the internal aldimine (1.9 Å) and in the external aldimine (2.4 Å) of the substrate analog L‐Dopa methylester. In this intermediate, the highly flexible AADC catalytic loop (CL) is captured in a closed state contacting all protein domains. In addition, each active site, composed by residues of both subunits, is connected to the other through weak interactions and a central cavity. By combining crystallographic analyses with all‐atom and coarse‐grained molecular dynamics simulations, SAXS investigations and limited proteolysis experiments, we realized that the functionally obligate homodimeric AADC enzyme in solution is an elongated, asymmetric molecule, where the fluctuations of the CL are coupled to flexibility at the edge between the N‐terminal and C‐terminal domains. The structural integrity of this peripheral protein region is essential to catalysis, as assessed by both artificial and 37 AADC deficiency pathogenic variants leading to the interpretation that structural dynamics in protein regions far from the active site is essential for CL flexibility and the acquirement of a correct catalytically competent structure. This could represent the molecular basis for pathogenicity prediction in AADC deficiency. [ABSTRACT FROM AUTHOR]

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Soil derived dissolved organic matter (DOM) is an important component of the carbon cycle and influences numerous biogeochemical processes, including the formation of mineral-organic associations. DOM ranges in size from small organic molecules to macromolecules and colloidal aggregates. In this study we have used small angle neutron (SANS) and X-ray (SAXS) scattering to characterize the colloidal DOM fraction from the organic layer of a boreal forest soil, and its interactions with hematite (α-Fe2O3) mineral nanoparticles. Comparison between SAXS and contrast variation SANS patterns revealed that the scattering form factor of the colloidal DOM aggregates was essentially independent of the scattering contrast, implying that the colloidal aggregates have an essentially homogeneous chemical composition, down to the nanometre length scale. Variation of the D2O/H2O ratio of the solvent yielded a SANS intensity minimum at ca. 40 ​vol % D2O, which was consistent with colloids composed of mainly polysaccharides. At pH 5.5 the pure hematite nanoparticles were colloidally stable in water and characterized by a ζ-potential of +25 ​mV and a hydrodynamic radius of ca. 70 ​nm. In the presence of DOM, the hematite nanoparticles lost the colloidal stability and aggregated into larger clusters, displaying a negative ζ-potential of ca. −25 ​mV. The charge reversal suggested that negatively charged polyanions of DOM adsorbed onto the hematite particles, possibly leading to bridging flocculation. Our results suggested that mainly low molecular weight components induced hematite aggregation because no or very limited interactions between DOM colloids and hematite were detected.

NifL is a conformationally dynamic flavoprotein responsible for regulating the activity of the σ54-dependent activator NifA to control the transcription of nitrogen fixation (nif) genes in response to intracellular oxygen, cellular energy, or nitrogen availability. The NifL-NifA two-component system is the master regulatory system for nitrogen fixation. NifL serves as a sensory protein, undergoing signal-dependent conformational changes that modulate its interaction with NifA, forming the NifL–NifA complex, which inhibits NifA activity in conditions unsuitable for nitrogen fixation. While NifL-NifA regulation is well understood, these conformationally flexible proteins have eluded previous attempts at structure determination. In work described here, we advance a structural model of the NifL dimer supported by a combination of scattering techniques and mass spectrometry (MS)-coupled structural analyses that report on the average structure in solution. Using a combination of small angle X-ray scattering-derived electron density maps and MS-coupled surface labeling, we investigate the conformational dynamics responsible for NifL oxygen and energy responses. Our results reveal conformational differences in the structure of NifL under reduced and oxidized conditions that provide the basis for a model for modulating NifLA complex formation in the regulation of nitrogen fixation in response to oxygen in the model diazotroph, Azotobacter vinelandii. [ABSTRACT FROM AUTHOR]