Search

In the present work we have investigated the oligomerization process of Fischer-Tropsch synthesis products - gasoline (C5-C10) and diesel (C11-C18) hydrocarbon fractions with a total olefin content (consisting mainly olefins with a branched isomeric chain) of 79.3 and 31.8 wt.%, respectively. Oligomerization was carried out by radical initiation method using azobisisobutyronitrile, benzoyl peroxide, dicumyl peroxide and methyl ethyl ketone peroxide (Butanox M-50) as initiators. It was established that the yield of the oligomerization process depending on the initiator used decreases in the following order: azobisisobutyronitrile > benzoyl peroxide > dicumyl peroxide > Butanox M-50. It was determined that when the oligomerization is carried out in polar solvents such as acetone and dichloromethane the yield of product increases by ~2.1 and ~1.7 times, respectively, while at the same time adding a non-polar solvent such as tetrachloromethane to the reaction mixture decreases the product yield by ~2.0 times. The optimal technological parameters for carrying out oligomerization process of synthetic gasoline and diesel fractions were determined: where azobisisobutyronitrile, content 0.5 wt.%., is used as an initiator, acetone as solvent, with reaction temperature of 200 °C, and duration of 12 hrs. under inert atmosphere. The product yield from the diesel fraction is 39.5 %, and from the synthetic gasoline fraction - 36.0 %. At the same time, in terms of characteristics, the oligomerization product of the diesel fraction showed properties similar to commercially available Base oil 3cSt (Group III), and the gasoline fraction showed properties on par with the commercially produced PAO-2 (Group IV). [ABSTRACT FROM AUTHOR]

The study of bacterial immune systems has recently gained momentum, revealing a fascinating trend: many systems form large supramolecular assemblies. Here, we examine the potential mechanisms underpinning the evolutionary success of these structures, draw parallels to eukaryotic immunity, and offer fresh perspectives to stimulate future research into bacterial immunity. [ABSTRACT FROM AUTHOR]

The reaction of sodium 2,4‐di‐tert‐butyl‐6‐(diphenylphos‐phino)phenolate (1, NaOArP) with TiIVCl4(THF)2 in a 2 : 1 molar ratio yielded TiIV(OArP)2Cl2 (2). The reduction of 2 with magnesium gave the dimeric titanium(III) compound [TiIII(OArP)2Cl]2 (3). In the presence of magnesium, compound 2 was found to catalyse the cyclotrimerization, acyclic oligomerisation, and hydrogenation of terminal alkynes. The complexes were characterised by single‐crystal X‐ray diffraction, optical spectroscopy, elemental analysis, and NMR or EPR spectroscopy, respectively. [ABSTRACT FROM AUTHOR]

Although the ability of Lewis acids to initiate oligomerisation or polymerisation of pyrroles and indoles is known, no reliable information was available on the structures of the complexes formed therewith. Using 1H NMR spectroscopy, an attempt has now been made to elucidate the structures of the complexes formed by the treatment of pyrroles and indoles with AlCl3. [ABSTRACT FROM AUTHOR]

Plasmodium falciparum heat shock protein 70-1 (PfHsp70-1) and PfHsp70-z are essential cytosol localised chaperones of the malaria parasite. The two chaperones functionally interact to drive folding of several parasite proteins. While PfHsp70-1 is regarded as a canonical Hsp70 chaperone, PfHsp70-z belongs to the Hsp110 subcluster. One of the distinctive features of PfHsp70-z is its unique linker segment which delineates it from canonical Hsp70. In the current study, we elucidated the role of the linker in regulating Hsp70 self-association and client selection. Using recombinant forms of PfHsp70-1, PfHsp70-z and E. coli Hsp70 (DnaK) and their respective linker switch mutants we investigated self-association of the chaperones using surface plasmon resonance (SPR) analysis. The effect of the changes on client selectivity was investigated on DnaK and its mutant through co-affinity chromatography coupled to LC-MS analysis. Our findings demonstrated that the linker is important for both Hsp70 self-association and client binding.

Aims: LysM containing-protein is widely distributed in all domains of life and this kind of protein is essential for various biological activities in living organisms. Rv1288, a LysM containing-protein with esterase, was found in Mycobacterium tuberculosis. Biophysical studies revealed that the protein is responsible for modulating lipid metabolism that enables pathogens to survive under extreme conditions and decrease the permeability of the pathogen's cell wall to drug therapeutic agents. However, recognition and interaction between the protein, lipid and carbohydrate moieties at the molecular level remains largely unknown and must be investigated. Therefore, a production of recombinant protein Rv1288 should be performed to aid the study. Methodology and results: In this study, we cloned the full-length cDNA of Rv1288 from M. tuberculosis strain H37Rv and expressed it in pET-24d- Escherichia coli BL21(DE3) cells. Affinity and size exclusion chromatography methods purified the protein, and its preliminary oligomerisation state was determined based on a calculated apparent molecular weight of the protein. Rv1288 was expressed as a soluble protein at 20 °C, induced with 1 mM of isopropyl β-D-1- thiogalactopyranoside (IPTG). The calculated apparent molecular weight suggested that the Rv1288 protein formed a hexamer in solution. Conclusion, significance and impact of study: All the methods involved in this study to produce the recombinant Rv1288-pET24d and its soluble protein in E. coli cells have been described. Hence, it can be implemented for future studies. [ABSTRACT FROM AUTHOR]

Peroxiredoxins play central roles in the detoxification of reactive oxygen species and have been modelled across multiple organisms using a variety of kinetic methods. However, the peroxiredoxin dimer-to-decamer transition has been underappreciated in these studies despite the 100-fold difference in activity between these forms. This is due to the lack of available kinetics and a theoretical framework for modelling this process. Using published isothermal titration calorimetry data, we obtained association and dissociation rate constants of 0.050 µM−4·s−1 and 0.055 s−1, respectively, for the dimer–decamer transition of human PRDX1. We developed an approach that greatly reduces the number of reactions and species needed to model the peroxiredoxin decamer oxidation cycle. Using these data, we simulated horse radish peroxidase competition and NADPH-oxidation linked assays and found that the dimer–decamer transition had an inhibition-like effect on peroxidase activity. Further, we incorporated this dimer–decamer topology and kinetics into a published and validated in vivo model of PRDX2 in the erythrocyte and found that it almost perfectly reconciled experimental and simulated responses of PRDX2 oxidation state to hydrogen peroxide insult. By accounting for the dimer–decamer transition of peroxiredoxins, we were able to resolve several discrepancies between experimental data and available kinetic models. [ABSTRACT FROM AUTHOR]

Other than triarylamines, which are protonated by strong acids both at their N‐atom and aromatic rings, pyrrole and its N‐substituted derivatives were exclusively protonated at the carbon atoms of their heteroaromatic rings. Whereas with the strong trifluoromethane sulfonic acid (TFS) stable pyrrolium salts were obtained, with the weaker trifluoroacetic acid (TFA) oligomers are formed. E.g. from the N‐(tert‐butyl)pyrrole a dimeric compound could be unambiguously identified and structural characterised by means of 1H NMR measurements. Treatment of N‐aryl substituted pyrroles with deuterated TFS revealed an H/D exchange not only at the pyrrole rings but also at their aryl moieties even. [ABSTRACT FROM AUTHOR]

The human RAD52 protein, which forms an oligomeric ring structure, is involved in DNA double‐strand break repair. The N‐terminal half of RAD52 is primarily responsible for self‐oligomerisation and DNA binding. Crystallographic studies have revealed the detailed structure of the N‐terminal half. However, only low‐resolution structures have been reported for the full‐length protein, and thus the structural role of the C‐terminal half in self‐oligomerisation has remained elusive. In this study, we determined the solution structure of the human RAD52 protein by cryo‐electron microscopy (cryo‐EM), at an average resolution of 3.5 Å. The structure revealed an undecameric ring that is nearly identical to the crystal structures of the N‐terminal half. The cryo‐EM map for the C‐terminal half was poorly defined, indicating that the region is intrinsically disordered. The present cryo‐EM structure provides important insights into the mechanistic roles played by the N‐terminal and C‐terminal halves of RAD52 during DNA double‐strand break repair.

Background: BFSP1 (beaded filament structural protein 1) is a plasma membrane, Aquaporin 0 (AQP0/MIP)-associated intermediate filament protein expressed in the eye lens. BFSP1 is myristoylated, a post-translation modification that requires caspase cleavage at D433. Bioinformatic analyses suggested that the sequences 434–452 were α-helical and amphipathic. Methods and Results: By CD spectroscopy, we show that the addition of trifluoroethanol induced a switch from an intrinsically disordered to a more α-helical conformation for the residues 434–467. Recombinantly produced BFSP1 fragments containing this amphipathic helix bind to lens lipid bilayers as determined by surface plasmon resonance (SPR). Lastly, we demonstrate by transient transfection of non-lens MCF7 cells that these same BFSP1 C-terminal sequences localise to plasma membranes and to cytoplasmic vesicles. These can be co-labelled with the vital dye, lysotracker, but other cell compartments, such as the nuclear and mitochondrial membranes, were negative. The N-terminal myristoylation of the amphipathic helix appeared not to change either the lipid affinity or membrane localisation of the BFSP1 polypeptides or fragments we assessed by SPR and transient transfection, but it did appear to enhance its helical content. Conclusions: These data support the conclusion that C-terminal sequences of human BFSP1 distal to the caspase site at G433 have independent membrane binding properties via an adjacent amphipathic helix. [ABSTRACT FROM AUTHOR]

For many inflammatory cytokines, the response elicited is dependent on the recruitment of the tumour necrosis factor receptor‐associated factor (TRAF) family of adaptor proteins. All TRAF proteins have a trimeric C‐terminal TRAF domain, while at the N‐terminus most TRAFs have a RING domain that forms dimers. The symmetry mismatch of the N‐ and C‐terminal halves of TRAF proteins means that when receptors cluster, it is presumed that RING dimers connect TRAF trimers to form a network. Here, using purified TRAF6 proteins, we provide direct evidence in support of this model, and we show that TRAF6 trimers bind Lys63‐linked ubiquitin chains to promote their processive assembly. This study provides critical evidence in support of TRAF trimers as key players in signalling. [ABSTRACT FROM AUTHOR]

The human RAD52 protein, which forms an oligomeric ring structure, is involved in DNA double‐strand break repair. The N‐terminal half of RAD52 is primarily responsible for self‐oligomerisation and DNA binding. Crystallographic studies have revealed the detailed structure of the N‐terminal half. However, only low‐resolution structures have been reported for the full‐length protein, and thus the structural role of the C‐terminal half in self‐oligomerisation has remained elusive. In this study, we determined the solution structure of the human RAD52 protein by cryo‐electron microscopy (cryo‐EM), at an average resolution of 3.5 Å. The structure revealed an undecameric ring that is nearly identical to the crystal structures of the N‐terminal half. The cryo‐EM map for the C‐terminal half was poorly defined, indicating that the region is intrinsically disordered. The present cryo‐EM structure provides important insights into the mechanistic roles played by the N‐terminal and C‐terminal halves of RAD52 during DNA double‐strand break repair. [ABSTRACT FROM AUTHOR]

Phenolic compounds are widely distributed in nature and industrial environment, and their detoxification or bioactive enhancement is of great value to environmental protection and industrial development. Laccases are multicopper oxidases that catalyse the oligo- or polymerisation of phenolic compounds. Identifying new laccase producers and investigating their application potential are of great importance. In this study, a white-rot fungus, Trametes hirsuta EZ1, with significantly high laccase productivity was isolated. The optimum conditions were studied for the maximum fermentation of extracellular laccase, which was achieved at 150 U/mL with a medium containing 10% strain EZ1, 7% maltodextrin, 1.5% peptone, and 0.5 mM Cu2+, and incubation at initial pH 6.0, 32 °C, and 180 rpm for nine days. Subsequently, a 70-kDa laccase was purified that showed activity over a wide range of temperature and pH, sensitivity to many metal ions and sodium dodecyl sulphate, and high tolerance to organic solvents. Purified laccase showed a significant unreported effect by catalysing catechol or ferulic acid into dimers, trimers, and tetramers or caffeic acid into dimers, trimers, tetramers, and pentamers. The oligomeric mixtures exhibited increased antioxidative capacity compared to that of each parent monomer, except for caffeic acid derivatives. Our study offers a novel strain source for laccase production and broadens its application in the enhancement of bioactive compounds. [Display omitted] • Isolation of a novel strain (Trametes hirsuta EZ1) with high laccase-productivity. • 150 U/mL of maximum yielding was achieved after fermentation optimization. • A 70-kDa single laccase was purified and performed valuable properties. • EZ1-laccase oligomerized three phenolic compounds into unfocused oligomers. • All oligomers performed altered antioxidative capacity and acceptable stability. [ABSTRACT FROM AUTHOR]

Peroxiredoxins play central roles in the detoxification of reactive oxygen species and have been modelled across multiple organisms using a variety of kinetic methods. However, the peroxiredoxin dimer-to-decamer transition has been underappreciated in these studies despite the 100-fold difference in activity between these forms. This is due to the lack of available kinetics and a theoretical framework for modelling this process. Using published isothermal titration calorimetry data, we obtained association and dissociation rate constants of 0.050 µM−4·s−1 and 0.055 s−1, respectively, for the dimer–decamer transition of human PRDX1. We developed an approach that greatly reduces the number of reactions and species needed to model the peroxiredoxin decamer oxidation cycle. Using these data, we simulated horse radish peroxidase competition and NADPH-oxidation linked assays and found that the dimer–decamer transition had an inhibition-like effect on peroxidase activity. Further, we incorporated this dimer–decamer topology and kinetics into a published and validated in vivo model of PRDX2 in the erythrocyte and found that it almost perfectly reconciled experimental and simulated responses of PRDX2 oxidation state to hydrogen peroxide insult. By accounting for the dimer–decamer transition of peroxiredoxins, we were able to resolve several discrepancies between experimental data and available kinetic models.

Alzheimer's disease (AD) is the most common dementia in the elderly and its increasing prevalence presents treatment challenges. Despite a better understanding of the disease, the current mainstay of treatment cannot modify pathogenesis or effectively address the associated cognitive and memory deficits. Emerging evidence suggests adenosine G protein-coupled receptors (GPCRs) are promising therapeutic targets for Alzheimer's disease. The adenosine A1 and A2A receptors are expressed in the human brain and have a proposed involvement in the pathogenesis of dementia. Targeting these receptors preclinically can mitigate pathogenic β-amyloid and tau neurotoxicity whilst improving cognition and memory. In this review, we provide an accessible summary of the literature on Alzheimer's disease and the therapeutic potential of A1 and A2A receptors. Although there are no available medicines targeting these receptors approved for treating dementia, we provide insights into some novel strategies, including allosterism and the targeting of oligomers, which may increase drug discovery success and enhance the therapeutic response. [ABSTRACT FROM AUTHOR]

TAR DNA-binding protein 43 (TDP-43) forms intraneuronal cytoplasmic inclusions associated with amyotrophic lateral sclerosis and ubiquitin-positive frontotemporal lobar degeneration. Its N-terminal domain (NTD) can dimerise/oligomerise with the head-to-tail arrangement, which is essential for function but also favours liquid-liquid phase separation and inclusion formation of full-length TDP-43. Using various biophysical approaches, we identified an alternative conformational state of NTD in the presence of Sulfobetaine 3-10 (SB3-10), with higher content of α-helical structure and tryptophan solvent exposure. NMR shows a highly mobile structure, with partially folded regions and β-sheet content decrease, with a concomitant increase of α-helical structure. It is monomeric and reverts to native oligomeric NTD upon SB3-10 dilution. The equilibrium GdnHCl-induced denaturation shows a cooperative folding and a somewhat lower conformational stability. When the aggregation processes were compared with and without pre-incubation with SB3-10, but at the identical final SB3-10 concentration, a slower aggregation was found in the former case, despite the reversible attainment of the native conformation in both cases. This was attributed to protein monomerization and oligomeric seeds disruption by the conditions promoting the alternative conformation. Overall, the results show a high plasticity of TDP-43 NTD and identify strategies to monomerise TDP-43 NTD for methodological and biomedical applications. [ABSTRACT FROM AUTHOR]

Background: BFSP1 (beaded filament structural protein 1) is a plasma membrane, Aquaporin 0 (AQP0/MIP)-associated intermediate filament protein expressed in the eye lens. BFSP1 is myristoylated, a post-translation modification that requires caspase cleavage at D433. Bioinformatic analyses suggested that the sequences 434–452 were α-helical and amphipathic. Methods and Results: By CD spectroscopy, we show that the addition of trifluoroethanol induced a switch from an intrinsically disordered to a more α-helical conformation for the residues 434–467. Recombinantly produced BFSP1 fragments containing this amphipathic helix bind to lens lipid bilayers as determined by surface plasmon resonance (SPR). Lastly, we demonstrate by transient transfection of non-lens MCF7 cells that these same BFSP1 C-terminal sequences localise to plasma membranes and to cytoplasmic vesicles. These can be co-labelled with the vital dye, lysotracker, but other cell compartments, such as the nuclear and mitochondrial membranes, were negative. The N-terminal myristoylation of the amphipathic helix appeared not to change either the lipid affinity or membrane localisation of the BFSP1 polypeptides or fragments we assessed by SPR and transient transfection, but it did appear to enhance its helical content. Conclusions: These data support the conclusion that C-terminal sequences of human BFSP1 distal to the caspase site at G433 have independent membrane binding properties via an adjacent amphipathic helix.

UV-induced oligomerisation of squalene was undertaken to indicate the potential for squalene-containing biological systems to exhibit rheology changes. DOSY NMR enabled the determination of the molecular weight (MW) range using Stokes–Einstein Gierer–Wirtz Estimation (SEGWE Calculator, University of Manchester). This approach was validated by Atmospheric Solids Analysis Probe Time of Flight Mass Spectrometry (ASAP TOF MS). To demonstrate the principle, both benzoyl peroxide and AIBN were used, separately, to initiate rapid, radical oligomerisation. Subsequent experiments in the absence of initiators compared the influence of UV wavelength and time on the resulting oligomer formation. To further model a relevant biological implication of this potentially chaotic UV oligomerisation, both saturated and unsaturated free fatty acids were added to squalene and exposed to UV at 285 nm and 300 nm to determine if cross oligomerisation could be observed. This representation of sebum evidenced the formation of a distribution of higher MW oligomers. Internal viscosity was normalised using the DMSO solvent, but to confirm that changes in rheology did not affect diffusion, a final experiment where fresh squalene was added to our oligomer mixture, representative of sebum, showed that unchanged squalene possessed the anticipated monomeric diffusion coefficient and hence MW. This work suggests, at least qualitatively, that UV-induced squalene oligomerisation can occur over time and that this may have a role in the behaviour of squalene on the skin. [ABSTRACT FROM AUTHOR]

The generation of diphosphorus molecules P2 under mild conditions in solution is a useful strategy to generate diphosphines via [4+2] cycloadditions. We recently described the release of P2 units from the nickel butterfly complex [{(IMes)Ni(CO)}2(μ2,η2:η2‐P2)] (IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene) upon addition of CO gas. Herein, we developed an alternative protocol for the same process using heterocumulenes. In addition to formation of P4 (the dimerisation product of P2), the reactions afford nickel complexes of novel pincer‐type ligands. Aryl isothiocyanates undergo a trimerisation within the coordination sphere of nickel and afford square planar nickel complexes with S−C−S pincer‐ligand frameworks. Carbon disulfide coordinates to the [(IMes)Ni]‐fragment in an η2‐fashion, affording a dinuclear complex. Similar products are formed when the N‐heterocyclic carbene nickel(0) complex [(IMes)Ni(vtms)2] is used as a precursor (vtms=vinyltrimethylsilane). [ABSTRACT FROM AUTHOR]

Autophagy is a highly conserved catabolic process cells use to maintain their homeostasis by degrading misfolded, damaged and excessive proteins, nonfunctional organelles, foreign pathogens and other cellular components. Hence, autophagy can be nonselective, where bulky portions of the cytoplasm are degraded upon stress, or a highly selective process, where preselected cellular components are degraded. To distinguish between different cellular components, autophagy employs selective autophagy receptors, which will link the cargo to the autophagy machinery, thereby sequestering it in the autophagosome for its subsequent degradation in the lysosome. Autophagy receptors undergo post‐translational and structural modifications to fulfil their role in autophagy, or upon executing their role, for their own degradation. We highlight the four most prominent protein modifications – phosphorylation, ubiquitination, acetylation and oligomerisation – that are essential for autophagy receptor recruitment, function and turnover. Understanding the regulation of selective autophagy receptors will provide deeper insights into the pathway and open up potential therapeutic avenues. [ABSTRACT FROM AUTHOR]

AtSWEET11 and AtSWEET12 are central players in phloem loading and long-distance sucrose translocation. During drought stress, these transporters enhance sucrose transport from shoot to root, increasing root proliferation. Chen et al. have now unravelled novel aspects of sucrose transport regulation, occurring via AtSWEET11 and AtSWEET12 phosphorylation and oligomerisation. [ABSTRACT FROM AUTHOR]

TAR DNA-binding protein 43 (TDP-43) forms intraneuronal cytoplasmic inclusions associated with amyotrophic lateral sclerosis and ubiquitin-positive frontotemporal lobar degeneration. Its N-terminal domain (NTD) can dimerise/oligomerise with the head-to-tail arrangement, which is essential for function but also favours liquid-liquid phase separation and inclusion formation of full-length TDP-43. Using various biophysical approaches, we identified an alternative conformational state of NTD in the presence of Sulfobetaine 3-10 (SB3-10), with higher content of α-helical structure and tryptophan solvent exposure. NMR shows a highly mobile structure, with partially folded regions and β-sheet content decrease, with a concomitant increase of α-helical structure. It is monomeric and reverts to native oligomeric NTD upon SB3-10 dilution. The equilibrium GdnHCl-induced denaturation shows a cooperative folding and a somewhat lower conformational stability. When the aggregation processes were compared with and without pre-incubation with SB3-10, but at the identical final SB3-10 concentration, a slower aggregation was found in the former case, despite the reversible attainment of the native conformation in both cases. This was attributed to protein monomerization and oligomeric seeds disruption by the conditions promoting the alternative conformation. Overall, the results show a high plasticity of TDP-43 NTD and identify strategies to monomerise TDP-43 NTD for methodological and biomedical applications.

UV-induced oligomerisation of squalene was undertaken to indicate the potential for squalene-containing biological systems to exhibit rheology changes. DOSY NMR enabled the determination of the molecular weight (MW) range using Stokes–Einstein Gierer–Wirtz Estimation (SEGWE Calculator, University of Manchester). This approach was validated by Atmospheric Solids Analysis Probe Time of Flight Mass Spectrometry (ASAP TOF MS). To demonstrate the principle, both benzoyl peroxide and AIBN were used, separately, to initiate rapid, radical oligomerisation. Subsequent experiments in the absence of initiators compared the influence of UV wavelength and time on the resulting oligomer formation. To further model a relevant biological implication of this potentially chaotic UV oligomerisation, both saturated and unsaturated free fatty acids were added to squalene and exposed to UV at 285 nm and 300 nm to determine if cross oligomerisation could be observed. This representation of sebum evidenced the formation of a distribution of higher MW oligomers. Internal viscosity was normalised using the DMSO solvent, but to confirm that changes in rheology did not affect diffusion, a final experiment where fresh squalene was added to our oligomer mixture, representative of sebum, showed that unchanged squalene possessed the anticipated monomeric diffusion coefficient and hence MW. This work suggests, at least qualitatively, that UV-induced squalene oligomerisation can occur over time and that this may have a role in the behaviour of squalene on the skin.

Tryptocidine C (TpcC, cyclo[D-Phe1-Pro2-Trp3-D-Trp4-Asn5-Gln6-Trp7-Val8-Orn9-Leu10]) is a broad-spectrum antimicrobial peptide in the tyrothricin complex produced by a soil bacterium, Brevibacillus parabrevis. Electrospray mass spectrometric studies reveal the oligomerisation of TpcC into dimers and higher oligomers, analogous to tyrocidine C (TrcC, Trp7 replaced by Tyr7). Ion mobility mass spectrometry (IMMS) further confirms the formation of stable peptide dimers and tetramers with diameters of 2.7 nm and 3.3 nm, respectively, calculated from collisional cross section (CCS). Molecular dynamic simulations and docking studies support the formation of amphipathic dimers, with a diameter of 2.5 ± 0.07 nm calculated from low energy model CCS. Circular dichroism and IMMS studies point towards dynamic hydrogen-bonded conformational changes up to 28–33 μM after which the structures become more static (or in equilibrium). Fluorescence studies indicate aromatic stacking of Trp residues with a CMC of 18 μM in aqueous solutions. The concentration and time dependent interaction of Trp in oligomers indicate cooperativity in the TpcC oligomerisation that leads to the formation of higher order microscopic structures. Scanning electron microscopy studies unequivocally shows that TpcC forms nanospheres with a mean diameter of 25 nm. Repeated smaller oligomeric units, possibly dimers and tetramers, self-assemble to form these nanospheres. Image 1 • Tryptocidine C (TpcC), an antimicrobial cyclodecapeptide from tyrothricin readily oligomerises into nano-assemblies. • Dimers, trimers, tetramers and higher oligomers of TpcC were observed with electrospray – and ion mobility mass spectrometry. • Circular dichroism and fluorescence studies indicated a H-bond network and cooperative aromatic stacking in TpcC oligomers. • Molecular modelling revealed beta-sheet type TpcC monomers and dimers with CCS values correlating with those determined by IMMS. [ABSTRACT FROM AUTHOR]

Protochlorophyllide oxidoreductase (POR) catalyses reduction of protochlorophyllide (Pchlide) to chlorophyllide, a light‐dependent reaction of chlorophyll biosynthesis. POR is also important in plant development as it is the main constituent of prolamellar bodies in etioplast membranes. Prolamellar bodies are highly organised, paracrystalline structures comprising aggregated oligomeric structures of POR–Pchlide–NADPH complexes. How these oligomeric structures are formed and the role of Pchlide in oligomerisation remains unclear. POR crystal structures highlight two peptide regions that form a 'lid' to the active site, and undergo conformational change on binding Pchlide. Here, we show that Pchlide binding triggers formation of large oligomers of POR using size exclusion chromatography. A POR 'octamer' has been isolated and its structure investigated by cryo‐electron microscopy at 7.7 Å resolution. This structure shows that oligomer formation is most likely driven by the interaction of amino acid residues in the highly conserved lid regions. Computational modelling indicates that Pchlide binding stabilises exposure of hydrophobic surfaces formed by the lid regions, which supports POR dimerisation and ultimately oligomer formation. Studies with variant PORs demonstrate that lid residues are involved in substrate binding and photocatalysis. These highly conserved lid regions therefore have a dual function. The lid residues position Pchlide optimally to enable photocatalysis. Following Pchlide binding, they also enable POR oligomerisation – a process that is reversed through subsequent photocatalysis in the early stages of chloroplast development. [ABSTRACT FROM AUTHOR]

Plasmodium falciparum heat shock protein 70-1 (PfHsp70-1) and PfHsp70-z are essential cytosol localised chaperones of the malaria parasite. The two chaperones functionally interact to drive folding of several parasite proteins. While PfHsp70-1 is regarded as a canonical Hsp70 chaperone, PfHsp70-z belongs to the Hsp110 subcluster. One of the distinctive features of PfHsp70-z is its unique linker segment which delineates it from canonical Hsp70. In the current study, we elucidated the role of the linker in regulating Hsp70 self-association and client selection. Using recombinant forms of PfHsp70-1, PfHsp70-z and E. coli Hsp70 (DnaK) and their respective linker switch mutants we investigated self-association of the chaperones using surface plasmon resonance (SPR) analysis. The effect of the changes on client selectivity was investigated on DnaK and its mutant through co-affinity chromatography coupled to LC-MS analysis. Our findings demonstrated that the linker is important for both Hsp70 self-association and client binding., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

The metazoan endoplasmic reticulum (ER) serves both as a hub for maturation of secreted proteins and as an intracellular calcium storage compartment, facilitating calcium-release-dependent cellular processes. ER calcium depletion robustly activates the unfolded protein response (UPR). However, it is unclear how fluctuations in ER calcium impact organellar proteostasis. Here, we report that calcium selectively affects the dynamics of the abundant metazoan ER Hsp70 chaperone BiP, by enhancing its affinity for ADP. In the calcium-replete ER, ADP rebinding to post-ATP hydrolysis BiP-substrate complexes competes with ATP binding during both spontaneous and co-chaperone-assisted nucleotide exchange, favouring substrate retention. Conversely, in the calcium-depleted ER, relative acceleration of ADP-to-ATP exchange favours substrate release. These findings explain the rapid dissociation of certain substrates from BiP observed in the calcium-depleted ER and suggest a mechanism for tuning ER quality control and coupling UPR activity to signals that mobilise ER calcium in secretory cells.

The study of pseudokinases has uncovered that catalysis‐independent functions play a critical role in cell signalling regulation. However, how pseudokinases dynamically assemble and regulate oncogenic signalling pathways remains, in most cases, unclear due to a limited knowledge of the structural determinants that are critical for their functions. Here, we review the recent progress made to unravel the role of the PEAK family of pseudokinases, which comprises SgK269, SgK223 and the recently identified PEAK3, in assembling specific oncogenic signalling pathways that contribute to the progression of several aggressive cancers. We focus on recent structural advances revealing that SgK269 and SgK223 can homo‐ and heteroassociate via a unique dimerisation domain, comprising conserved regulatory helices directly surrounding the pseudokinase domain, which is also conserved in PEAK3. We also highlight a potential oligomerisation mechanism driven by the pseudokinase domain. While it is likely that homo‐ or heterodimerisation and oligomerisation mechanisms contribute to the assembly of complex signalling hubs and provide a means to spatially and temporally modulate and diversify signalling outputs, the exact role that these oncogenic scaffolds play in regulating cell migration, invasion and morphology remains unclear. Here, we attempt to link their structural characteristics to their cellular functions by providing a thorough analysis of the signalling transduction pathways they are known to modulate. [ABSTRACT FROM AUTHOR]

Linear α-olefins or LAOs are produced by the catalytic oligomerisation of ethylene on a multimillion ton scale annually. A range of LAOs is typically obtained with varying chain lengths which follow a distribution. Depending on the catalyst, various types of distributions have been identified, such as Schulz–Flory, Poisson, alternating and selective oligomerisations such as ethylene trimerisation to 1-hexene and tetramerisation to 1-octene. A comprehensive mathematical analysis for all oligomer distributions is presented, showing the relations between the various distributions and with ethylene polymerisation, as well as providing mechanistic insight into the underlying chemical processes. [ABSTRACT FROM AUTHOR]

Tight junctions regulate paracellular permeability size and charge selectively. Models have been proposed for the molecular architecture of tight junction strands and paracellular channels. However, they are not fully consistent with experimental and structural data. Here, we analysed the architecture of claudin-based tight junction strands and channels by cellular reconstitution of strands, structure-guided mutagenesis, in silico protein docking and oligomer modelling. Prototypic channel- (Cldn10b) and barrier-forming (Cldn3) claudins were analysed. Förster resonance energy transfer (FRET) assays indicated multistep claudin polymerisation, starting with cis -oligomerization specific to the claudin subtype, followed by trans- interaction-triggered cis -polymerisation. Alternative protomer interfaces were modelled in silico and tested by cysteine-mediated crosslinking, confocal- and freeze fracture EM-based analysis of strand formation. The analysed claudin mutants included also mutations causing the HELIX syndrome. The results indicated that protomers in Cldn10b and Cldn3 strands form similar antiparallel double rows, as has been suggested for Cldn15. Mutually stabilising ‐hydrophilic and hydrophobic ‐ cis- and trans- interfaces were identified that contained novel key residues of extracellular segments ECS1 and ECS2. Hydrophobic clustering of the flexible ECS1 β1β2 loops together with ECS2–ECS2 trans- interaction is suggested to be the driving force for conjunction of tetrameric building blocks into claudin polymers. Cldn10b and Cldn3 are indicated to share this polymerisation mechanism. However, in the paracellular centre of tetramers, electrostatic repulsion may lead to formation of pores (Cldn10b) and electrostatic attraction to barriers (Cldn3). Combining in vitro data and in silico modelling, this study improves mechanistic understanding of paracellular permeability regulation by elucidating claudin assembly and its pathologic alteration as in HELIX syndrome. Unlabelled Image • Multistep polymerisation of claudins is driven by mutual stabilisation of cis - and trans -interfaces. • Claudin-3 and -10b differ in oligomerization but share similar face-to-face double-row architecture in strands. • Strand polymerisation occurs independent of channel versus barrier conformation. • Structural keys for claudin assembly determining paracellular permeability were identified. [ABSTRACT FROM AUTHOR]

Despite extensive research carried out on lupin seed γ-conglutin neither its mechanism of action as a hypoglycaemic nutraceutical compound nor its physiological role for the plant has been unveil. This article revealed a pH-dependent reversible association/dissociation equilibrium involving monomer, dimer and hexamer of Lupinus angustifolius γ-conglutin. The interaction between different oligomeric forms of this protein is reversible, and spectroscopic studies showed that the intact structure of γ-conglutin was preserved under the tested environmental conditions tested (pH 4.5–7.5). The obtained results prove that the hexameric form was preferred under basic conditions and was stabilised by a number of bonds formed upon association of individual protomers. The simultaneous occurrence of several oligomeric forms at a given pH value was shown, and their share was strongly driven by protein concentration. The main changes in oligomerisation of γ-conglutin take place in a pH range of 4.5–6.0, correlating with the pKa R values of the amino acid residues of His (6.0), Glu (4.1), and Asp (3.9). Moreover, a structural model of the protein in hexamer assembly was obtained based on small-angle X-ray scattering (SAXS) and negative staining cryo-electron microscopy (cryo-EM) analyses. The presented study provides essential knowledge about the colloidal dynamics and stability of γ-conglutin in solution, improving our understanding of fundamental environmental factors that could affect the health-promoting activity of this lupin seed protein. [Display omitted] • γ-Conglutin undergoes a pH-dependent reversible association/dissociation equilibrium. • The simultaneous occurrence of several oligomeric forms at a given pH value was shown. • The share of particular oligomeric form was strongly driven by protein concentration. • Spectroscopic studies showed that the intact structure of γ-conglutin was preserved. • The main changes in oligomerisation take place in a pH range of 4.5–6.0 [ABSTRACT FROM AUTHOR]

Ketol-acid reductoisomerase (KARI) orchestrates the biosynthesis of branched-chain amino acids, an elementary reaction in prototrophic organisms as well as a valuable process in biotechnology. Bacterial KARIs belonging to class I organise as dimers or dodecamers and were intensively studied to understand their remarkable specificity towards NADH or NADPH, but also to develop antibiotics. Here, we present the first structural study on a KARI natively isolated from a methanogenic archaea. The dodecameric structure of 0.44-MDa was obtained in two different conformations, an open and close state refined to a resolution of 2.2-Å and 2.1-Å, respectively. These structures illustrate the conformational movement required for substrate and coenzyme binding. While the close state presents the complete NADP bound in front of a partially occupied Mg2+-site, the Mg2+-free open state contains a tartrate at the nicotinamide location and a bound NADP with the adenine-nicotinamide protruding out of the active site. Structural comparisons show a very high conservation of the active site environment and detailed analyses point towards few specific residues required for the dodecamerisation. These residues are not conserved in other dodecameric KARIs that stabilise their trimeric interface differently, suggesting that dodecamerisation, the cellular role of which is still unknown, might have occurred several times in the evolution of KARIs.

PB1-F2 is a non-structural protein of influenza A viruses (IAV) that modulates viral pathogenesis in a host-specific manner. In mammals, this protein has been shown to increase IAV virulence by delaying the early immune response and, eventually, exacerbating lung inflammation at the late stage of infection. PB1-F2 is a small protein, but displays very high sequence polymorphism and sequence length disparity depending on viral strain. These features result in strong variations in the cellular activity of PB1-F2. Studies have also reported that the effect of PB1-F2 is cell-type dependent. It has notably been shown that PB1-F2 can promote apoptosis in immune cells, but not in epithelial cells. This phenomenon appears to be partly related to the higher order structure of the protein, given that the presence of PB1-F2 β-aggregated structures in infected immune cells correlates with cell death induction. In this work, we evaluated, by synchrotron Fourier transform infrared spectromicroscopy, the impact of the transient expression of PB1-F2 on the biochemical composition of the human epithelial cell line HEK293T. Two PB1-F2 variants that are closely related to each other but derived from a strain with high [A/BrevigMission/1/1918 (H1N1)] or a low [A/WSN/1933 (H1N1)] virulence were studied here. Infrared spectra analysis revealed no specific enrichment of β-aggregated structures in PB1-F2-expressing cells. Nevertheless, this analysis suggested that there is a higher content of β-sheet secondary structures in the PB1-F2 from A/WSN/1933 than that from A/BrevigMission/1/1918. Our data also showed no change in membrane composition in the presence of PB1-F2, implying that PB1-F2 does not promote apoptosis in HEK293T cells. Finally, we found that the PB1-F2 from A/WSN/1933 interferes with adenosine triphosphate production, suggesting that this PB1-F2 variant may disturb the mitochondrial activity.

The oligomerisation of light olefins, obtainable from fossil/renewable sources and refinery streams, is an attractive route to produce clean synthetic fuels and added‐value chemicals. ZSM‐5 is a type of catalyst used in commercial olefin oligomerisation processes. Using appropriate modification procedures, it was possible to prepare catalysts with improved performances. Various modified versions of commercially available ZSM‐5 were prepared and investigated for 1‐butene oligomerisation under high‐pressure, continuous‐flow operation (30 bar, 200 °C). Simple, up‐scalable top‐down strategies involving base‐acid treatments of ZSM‐5 led to catalysts possessing enlarged pores and the required acidity for converting 1‐butene to higher molar mass products. In targeting diesel type products, the modified catalysts led to up to 86 % butenes conversion, space time yield of 852 mg gcat−1 h−1 and mass ratio diesel:naphtha cuts of 2.2. Characterisation studies and multivariate/principal component analysis helped categorise the differently prepared catalysts, and gain insights into complex interplay of material properties influencing the catalytic reaction. [ABSTRACT FROM AUTHOR]

Abstract The oligomerisation of 1-butene was studied under high-pressure continuous-flow conditions (200–250 °C, 30–40 bar), in the presence of micro/mesoporous zeotypes based on the MFI topology, which were prepared via different non-destructive bottom-up strategies: crystallization of silanized protozeolitic units; co-templating with a dual function (polymeric) template; and using a sole structure directing agent (non-surfactant and non-polymeric) to generate mesoporosity. The synthesis method influenced the material properties and consequently the catalytic performance. In targeting hydrocarbons with boiling point ranges characteristics of diesel, the zeotypes benefited from regular morphology, reduced crystallite size, mesoporosity and enhanced molar ratio of Lewis (L) to Brønsted (B) acid sites (L/B). In general, the zeotypes outperformed commercial zeolite ZSM-5. The best-performing zeotype was prepared according to the Serrano strategy based on the crystallization of silanized zeolitic seeds, and led to 97% conversion and an average space-time yield of liquid products of 1077 mg g cat −1 h−1, at 250 °C, 40 bar. The zeotypes seemed more stable than the commercial zeolite, based on molecular level characterization studies of the used/regenerated catalysts, with some differences in catalytic activity. Graphical abstract Image 1 Highlights • Olefins to diesel type products via oligomerisation over MFI-based catalysts. • Non-destructive synthetic bottom-up approaches to micro/mesoporous nano-zeotypes. • Regular morphology, nanocrystallites, mesoporosity, L/B favour catalytic performance. • Zeotypes outperformed commercial ZSM-5 which possessed greater amount of acid sites. [ABSTRACT FROM AUTHOR]

Synaptobrevin-2 is a key player in signal transmission in neurons. It forms, together with SNAP25 and Syntaxin-1A, the neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex and mediates exocytosis of synaptic vesicles with the pre-synaptic membrane. While Synaptobrevin-2 is part of a four-helix bundle in this SNARE complex, it is natively unstructured in the absence of lipids or other SNARE proteins. Partially folded segments, presumably SNARE complex formation intermediates, as well as formation of Synaptobrevin-2 dimers and oligomers, were identified in previous studies. Here, we employ three Synaptobrevin-2 variants—the full-length protein Syb(1-116), the soluble, cytosolic variant Syb(1-96) as well as a shorter version Syb(49-96) containing structured segments but omitting a trigger site for SNARE complex formation—to study oligomerisation in the absence of interaction partners or when incorporated into the lipid bilayer of liposomes. Combining native mass spectrometry with chemical cross-linking, we find that the truncated versions show increased oligomerisation. Our findings from both techniques agree well and confirm the presence of oligomers in solution while membrane-bound Synaptobrevin-2 is mostly monomeric. Using ion mobility mass spectrometry, we could further show that lower charge states of Syb(49-96) oligomers, which most likely represent solution structures, follow an isotropic growth curve suggesting that they are intrinsically disordered. From a technical point of view, we show that the combination of native ion mobility mass spectrometry with chemical cross-linking is well-suited for the analysis of protein homo-oligomers.ᅟ [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Process conditions have a major effect on the competition between ethylene oligomerisation and ethylene polymerisation. • Optimisation of process conditions drastically reduced solids that were obtained from sulfur-based ligands. • Catalysts that were overlooked due to high solids formation can be improved by simply optimising the process conditions. Abstract Sulfur-based bidentate ligands are active in Cr-catalysed selective ethylene oligomerisation but generally produce large amounts of solids. Through a systematic process condition optimisation study, the amount of solids formed with two P,S-bidentate ligands was reduced from 88% and 57% to 13% and 6% respectively, while maintaining reasonable oligomerisation activities and achieving high liquid product selectivities (>50% 1-octene and >75% 1-hexene and 1-octene combined). The selective suppression of solids formation indicated that ethylene oligomerisation and polymerisation reactions are possibly facilitated by different catalytic species. [ABSTRACT FROM AUTHOR]

Highlights • Endocannabinoid signaling is one of the most extensive systems of the mammalian brain. • Numerous described factors inflect eCB signaling. • Receptors oligomerisation substantially changes signalization they trigger. • The eCB system can be used as therapeutic target. Abstract The endocannabinoid (eCB) signaling system is one of the most extensive of the mammalian brain. Despite the involvement of only few specific ligands and receptors, the system encompasses a vast diversity of triggered mechanisms and driven effects. It mediates a wide range of phenomena, including the regulation of transmitter release, neural excitability, synaptic plasticity, impulse spread, long-term neuronal potentiation, neurogenesis, cell death, lineage segregation, cell migration, inflammation, oxidative stress, nociception and the sleep cycle. It is also known to be involved in the processes of learning and memory formation. This extensive scope of action is attained by combining numerous variables. In a properly functioning brain, the correlations of these variables are kept in a strictly controlled balance; however, this balance is disrupted in many pathological conditions. However, while this balance is known to be disrupted by drugs in the case of addicts, the stimuli and mechanisms influencing the neurodegenerating brain remain elusive. This review examines the multiple factors and phenomena affecting the eCB signaling system in the brain. It evaluates techniques of controlling the eCB system to identify the obstacles in their applications and highlights the crucial interdependent variables that may influence biomedical research outcomes. [ABSTRACT FROM AUTHOR]

Two-component signal transduction systems (TCSs) consist of sensor histidine kinases and response regulators. TCSs mediate adaptation to environmental changes in bacteria, plants, fungi and protists. Histidine kinase 2 (Hik2) is a sensor histidine kinase found in all known cyanobacteria and as chloroplast sensor kinase in eukaryotic algae and plants. Sodium ions have been shown to inhibit the autophosphorylation activity of Hik2 that precedes phosphoryl transfer to response regulators, but the mechanism of inhibition has not been determined. We report on the mechanism of Hik2 activation and inactivation probed by chemical cross-linking and size exclusion chromatography together with direct visualisation of the kinase using negative-stain transmission electron microscopy of single particles. We show that the functional form of Hik2 is a higher-order oligomer such as a hexamer or octamer. Increased NaCl concentration converts the active hexamer into an inactive tetramer. The action of NaCl appears to be confined to the Hik2 kinase domain. [ABSTRACT FROM AUTHOR]

Sequential treatment of a previously-calcined solid oxide support (i.e. SiO2, γ-Al2O3, or mixed SiO2-Al2O3) with solutions of Cr{N(SiMe3)2}3 (0.71 wt% Cr) and a Lewis acidic alkyl aluminium-based co-catalyst (15 molar equivalents) affords initiator systems active for the oligomerisation and/or polymerisation of ethylene. The influence of the oxide support, calcination temperature, co-catalyst, and reaction diluent on both the productivity and selectivity of the immobilised chromium initiator systems have been investigated, with the best performing combination (SiO2−600, modified methyl aluminoxane-12 {MMAO-12}, heptane) producing a mixture of hexenes (61 wt%; 79% 1-hexene), and polyethylene (16 wt%) with an activity of 2403 g gCr−1 h−1. The observed product distribution is rationalised by two competing processes: trimerisation via a supported metallacycle-based mechanism and polymerisation through a classical Cossee-Arlman chain-growth pathway. This is supported by the indirect observation of two distinct chromium environments at the surface of the oxide support by a solid-state 29Si NMR spectroscopic study of the Cr{N(SiMe3)2}x/SiO2−600 pro-initiator. [ABSTRACT FROM AUTHOR]

A series of nickel(II) bromide complexes, [NiBr 2 (SeˆOˆN)] ( Ni1 – Ni4 ), supported by selenium-based tridentate ligands were prepared in good yields by reacting arylselenyl-ether-pyrazolyl ligands ( L1 – L4 ) with NiBr 2 (DME) (DME = 1,2-dimethoxyethane). All complexes were characterised by infrared spectroscopy, elemental analysis and high-resolution mass spectrometry. The crystallisation of Ni2 in THF/Et 2 O leads to the formation of a trimeric nickel complex, Ni2a·THF . X-ray crystallographic analyses of Ni2a·THF confirm the tridentate character of the SeˆOˆN ligand. Upon activation with methylaluminoxane (MAO), Ni1 – Ni4 complexes showed moderate to good activities for ethylene oligomerisation (TOF = 4.3–25.7 × 10 3 (mol ethylene) (mol Ni) −1  h −1 ), giving predominantly 1-butene (89.2–94.3 wt.%) as the main product. The ligand environment, i.e., the substituents on the pyrazolyl unit, as well as the reaction parameters, influence the catalytic activity towards the production of 1-butene. Under optimised reaction conditions (toluene, 500 equiv. of MAO, 30 °C and 20 min), the Ni4 /MAO catalytic system achieved TOF values up to 47.2 × 10 3 (mol ethylene) (mol Ni) −1  h −1 with good selectivity for α-C 4 (83.8 wt.%). [ABSTRACT FROM AUTHOR]