Archives of Biochemistry and Biophysics

The inactivation of the electrogenic function of the transmembrane sodium transporter in oxidative stress conditions has been intrinsically linked with the oxidation of its catalytically essential thiols. However, the spatial proximity of these catalytically relevant thiols is yet to be fully elucidated and thus still open. Herein, the influence of a thiol cross-linking [diamide, DA (0.1-2mM)] and a thiol alkylating [iodoacetamide, IA (0.1-5mM)] agent on the activity of the synaptosomal Na+/K+-ATPase were determined. In addition, the ability of dithiothreitol to either prevent or reverse the inhibition imposed by the thiol modifiers on the enzyme activity was also evaluated. The results showed that the thiol cross-linker inactivates the electrogenic function of the synaptosomal Na+/K+-ATPase when exposed to the thiols located at either the nucleotide or cation-binding sites. Conversely, irrespective of the exposed active sites, the thiol alkylating agents have no overt effect on the activity of the pump. Furthermore, dithiothreitol markedly prevented but did not reverse the inactivation of the electrogenic pump caused by cross-linking of its critical thiols. Interestingly, both the thiol cross-linker and alkylating agents markedly oxidize dithiothreitol in a time and concentration-dependent fashion. Consequently, within the limit of the present data, it appears that the catalytically relevant thiols of the transmembrane electrogenic pump located at the cationic and nucleotide binding sites, are in close proximity sufficient enough to allow for their cross-linking. HighlightsO_LIThe presence of Na+/K+-ATPase catalytically important thiols at the nucleotide and cationic sites of the enzyme define its vulnerability to oxidative assault. C_LIO_LIThe spatial location of these thiols at vicinal positions at these domains favour the formation of disulphide linkages under oxidative conditions C_LIO_LIThe disulphide crosslinking of these thiols culminate in enzyme inactivation C_LIO_LIThe inactivation can be prevented but not reversed by exogenous thiol compound C_LI

Erythrocyte death by eryptosis or erythronecrosis may induce erythrocyte shrinking or swelling with increase in osmotic resistance or fragility as indication of cytotoxicity. We investigated heterogeneous cytotoxic outcomes during in vitro exposure of goat erythrocytes to aluminium chloride, lead acetate or mercuric chloride using erythrocyte osmotic fragility (EOF) testing. The metallic salt solution (MSS) was added to 4.0 L of high (100 mosmol/L) and low (250 mosmol/L) hyposmolar sucrose media at 0.3 or 0.4 mosmol/L concentration during testing of the osmotic fragility of 5.0 L of blood from 10 goats. Hemolysis induced in the media (with and without MSS) was estimated in the supernatant with spectrophotometer at 540 nm. Osmotic stabilization or destabilization was calculated with probability for each test. Inducible osmotic resistance (IOR) was the ratio of mean stabilization to destabilization in both high and low hyposmolar media. Each MSS induced both osmotic resistance (stabilization) and fragility (destabilization) in varied media concentrations, with greater likelihood (P) of stabilization (0.93) or destabilization (0.77) in high or low media hyposmolarity, respectively. The EOF outcomes of the goats diverged within the group. High IOR induced by mercuric chloride (2.90) and low IOR by lead acetate (0.07) and aluminium chloride (0.04) reflected high stabilizing and destabilizing outcomes, respectively. In conclusion, MSS induced dual EOF outcomes (stabilization or destabilization) on the fragility domain, suggesting occurrence of both eryptosis (as stabilization) and erythronecrosis (as destabilization) at low exposure level, whereby biphasic, nonmonotonic or hormetic response to MSS toxic action might exist.

Cu/Zn Superoxide Dismutase 1 (SOD1) is a 32-kDa cytosolic dimeric metalloenzyme that neutralizes superoxide anions into harmless oxygen and hydrogen peroxide. Mutations in SOD1 are associated with ALS, a disease causing motor neuron atrophy and subsequent mortality. These mutations exert their harmful effects through a gain of function mechanism, rather than loss of function. Despite extensive research, the specific mechanism causing selective motor neuron death still remains unclear. A defining feature of ALS pathogenesis is protein misfolding and aggregation, evidenced by ubiquitinated protein inclusions containing SOD1 in motor neurons. This work aims to identify compounds countering SOD1(A4V) misfolding and aggregation, potentially aiding ALS treatment. The approach employed is drug repurposing and in vitro screening of a 1280 pharmacologically active compounds library, LOPAC(R). Using Differential Scanning Fluorimetry Technique (DSF), compounds were tested for their impact on SOD1(A4V) thermal stability. Screening revealed one compound raising protein-ligand Tm by 7{degrees}C, eight inducing a higher second Tm, suggesting stabilzation effect, and five reducing Tm up to 18{degrees}C, suggesting possible interactions or non-specific binding.

Misfolding and aggregation of TDP-43 protein are implicated in several proteinopathies like ALS and FTLD. Extracellular TDP-43 is also proposed to propagate in a prion-like pathogenic manner to the neighbouring cells. Here, using turbidity and sedimentation assay, we show that a polyphenol in green tea, epigallocatechin gallate (EGCG), can inhibit the in vitro aggregation of the full-length TDP-43 protein. Furthermore, Alexa-Fluor-labelled TDP-43 protein failed to show aggregates in the presence of EGCG in fluorescence microscopy. Also, AFM imaging revealed that EGCG co-incubation with TDP-43 allows formation of only small oligomers in contrast to the larger TDP-43 aggregates formed otherwise. A physical binding of EGCG with TDP-43 was observed using triphenyl tetrazolium chloride (TTC) staining and isothermal titration calorimetry (ITC). ITC also revealed a high-affinity binding site for EGCG on TDP-43 with a Kd value of 7.8 {micro}M and a binding free energy of -6.9 kcal/mol. Furthermore, in silico molecular docking and molecular dynamic simulation (MDS) studies using different available structures of the N-terminal, RRM1-2 and C-terminal domains of TDP-43, predicted a preferable and stable binding of EGCG to the structure of the aggregation prone C-terminal domain (CTD) (PDB ID:7KWZ). Also, EGCG complexed with CTD of TDP-43 yielded a negative {Delta}G value of -20.29 kcal/mol using MM-PBSA analysis of the MDS data thereby further suggesting a stable complex formation. Also, in MDS, EGCG interacted with the amino acids Phe-313 and Ala-341 of TDP-43, which were previously projected to be important for the recruitment of monomers for the amyloid formation by CTD, thereby suggesting a possible mechanism of EGCGs inhibition of the TDP-43 aggregation. Notably, while the in vitro-made aggregates of full-length TDP-43 caused mild cytotoxicity to the HEK293 cells, the small oligomers of TDP-43 formed in presence of EGCG did not. In totality, EGCG can in vitro interact with TDP-43 and inhibit its aggregation, possibly via interaction with the amyloidogenic domain, thereby preventing it from assuming cytotoxic conformations. As EGCG is a natural molecule, it could be relevant to the therapeutic quest against the TDP-43 proteinopathies.

Age-related neurodegenerative disorders like Alzheimers disease (AD) and Parkinsons disease (PD) are characterized by deposits of protein aggregates, or amyloid, in various regions of the brain. Traditionally, aggregation of a single protein was observed to be correlated with these different pathologies: tau in AD and -synuclein (S) in PD. However, there is increasing evidence that the pathologies of these two diseases overlap, and the individual proteins may promote each others aggregation. Both tau and S are intrinsically disordered proteins (IDPs), lacking stable secondary and tertiary structure under physiological conditions. In this study we used a combination of biochemical and biophysical techniques to interrogate the interaction of tau with both soluble and fibrillar S. Fluorescence correlation spectroscopy (FCS) was used to assess the interactions of specific domains of fluorescently labeled tau with full length and C-terminally truncated S in both monomeric and fibrillar forms. We found that full-length tau as well as individual tau domains interact with monomer S weakly, but this interaction is much more pronounced with S seeds. This interaction does not impact tau aggregation or fibril formation. These findings provide insight into the nature of interactions between tau and S as well as the domains responsible.

The S100 family consists of calcium binding proteins that are largely known for their contribution to the neuroinflammatory processes. They are associated with various cardiac and neurological functions as well as related diseases. A few S100 proteins can form unspecific or amyloid aggregates in neuropathologies and thus play a part in dementia pathogenesis. Among all S100 proteins, S100B and S100A9 aggregation properties are the most investigated, however, there is a lack of studies regarding other S100 members. In particular, S100A1 and S100A8 are also associated with neuropathies, but their interactions or aggregation are poorly understood. Therefore, in this study, we explored whether S100A1 and S100A8 proteins can form heterodimers, interact or co-aggregate. Our results revealed that S100A1 and S100A8 interactions and amyloid aggregation are driven by calcium ions. We observed that while S100A1 remains mostly stable, S100A8 forms various types of spherical or unspecific aggregates. While they do not form stable heterodimers like calprotectin, their transient interactions facilitate the formation of worm-like amyloid fibrils and the process is regulated by different calcium ion concentrations. At calcium ions saturation, both proteins are stabilized leading to inhibition of aggregation. Overall, by employing a diverse range of techniques from amyloid and protein-specific fluorescence detection to electron-electron double resonance spectroscopy, we elucidated interactions between S100 proteins that might otherwise be overlooked, enhancing our understanding of their aggregation behaviour.

BackgroundCytochrome b5 reductase is a flavoprotein that transfers electrons from NADH to multiple electron acceptors, such as cytochrome b5 or ubiquinone. Hysteresis is a phenomenon characterized by a slow transition between active and inactive catalytic states, leading to a lag phase in enzymatic activity. In this study, the effect of the soluble analogue of ubiquinone named 2,3 dimethoxy-5-methyl-1,4 benzoquinone (CoQ0) on the NADH:Cb5 reductase activity of recombinant human soluble Cb5R, using recombinant human soluble Cb5 as a substrate was evaluated. The aim of this study was to determine whether ubiquinone exerts a hysteretic modulation of this activity based on previous studies supporting that microsomal reduction of cytochrome b5 is controlled by redox hysteresis. ResultsThe NADH:cytochrome b5 reductase activity of Cb5R was characterized at different concentrations of Cb5R, cytochrome b5, and CoQ0 by monitoring the reduction of cytochrome b5. The addition of CoQ0 induced the appearance of a lag phase, whose duration increased with the concentration of CoQ0 and decreased with higher concentrations of cytochrome b5 or Cb5R. Additionally, a concentration-dependent decrease in the maximum rate of reduction and the appearance of positive cooperativity was observed in the presence of CoQ0 which resulted in leading to lower KM values for cytochrome b5. This suggests the formation of a CoQ0:Cb5R complex altering the interaction between the reductase and cytochrome b5 which increases the affinity for cytochrome b5. Cyclic voltammetry data support the formation of CoQ0/protein complex that could be responsible for the hysteretic behavior. ConclusionsThese results support the hypothesis that CoQ0 is a hysteretic modulator and inhibitor of the NADH: cytochrome b5 reductase activity of human Cb5R.

Huntingtons disease (HD) is caused by CAG repeat expansion in the huntingtin (HTT) gene. Skeletal muscle wasting alongside central pathology is a well-recognized phenomenon seen in patients with HD and HD mouse models. HD muscle atrophy progresses with disease and affects prognosis and quality of life. Satellite cells, progenitors of mature skeletal muscle fibers, are essential for proliferation, differentiation, and repair of muscle tissue in response to muscle injury or exercise. In this study, we aim to investigate the effect of mutant HTT on the differentiation and regeneration capacity of HD muscle by employing in vitro mononuclear skeletal muscle cell isolation and in vivo acute muscle damage model in R6/2 mice. We found that, similar to R6/2 adult mice, neonatal R6/2 mice also exhibit a significant reduction in myofiber width and morphological changes in gastrocnemius and soleus muscles compared to WT mice. Cardiotoxin (CTX)-induced acute muscle damage in R6/2 and WT mice showed that the Pax7+ satellite cell pool was dampened in R6/2 mice at 4 weeks post-injection, and R6/2 mice exhibited an altered inflammatory profile in response to acute damage. Our results suggest that, in addition to the mutant HTT degenerative effects in mature muscle fibers, expression of mutant HTT in satellite cells might alter developmental and regenerative processes to contribute to the progressive muscle mass loss in HD. Taken together, the results presented here encourage further studies evaluating the underlying mechanisms of satellite cell dysfunction in HD mouse models.

Risperidone is a second-generation antipsychotic widely prescribed for a variety of psychiatric disorders. Despite its widespread use, its subacute effects on oxidative metabolism in brain and liver tissues remain poorly understood. This study aimed to evaluate the impact of risperidone on antioxidant enzyme activity and lipid peroxidation in rats. A total of fifteen male Holtzman albino rats were randomly assigned to a Control group (n=5, no risperidone) and two treatment groups (n=5 per group) receiving 0.4 mg kg-1 day-1 and 4.0 mg kg-1 day-1 risperidone, administered via orogastric gavage for 20 consecutive days. After treatment, brain and liver tissues were collected. The activity of Superoxide Dismutase (SOD), Catalase (CAT), Glutathione Peroxidase (GPx), Glucose-6-Phosphate Dehydrogenase (G6PDH), and Glutathione S-Transferase (GST) was analyzed. Reduced Glutathione (GSH) levels and lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS), were quantified. Findings indicate that in brain tissue, both doses significantly increased CAT activity and decreased the SOD/CAT ratio, and that the high dose significantly reduced TBARS levels. In liver tissue, a significant increase in CAT activity was observed with the high dose. Furthermore, both doses significantly increased G6PDH activity and reduced TBARS levels. These results underscore the influence of risperidone on cerebral and hepatic oxidative metabolism during the subacute phase.

Protein fibrils are pathological hallmarks of many neurodegenerative diseases, including Parkinsons disease. The preparation of -synuclein (Syn) fibrils in vitro is widely used in research relating to these conditions. However, Syn fibrils exhibit substantial structural polymorphism. How fibril morphology evolves during formation, storage, or in the presence of small molecule ligands is poorly understood. Here, the evolution of Syn fibril morphology was investigated using fluorescence assays, circular dichroism, transmission electron microscopy, and ligand profiling. Fibril morphology was found to evolve continuously during both aggregation of Syn and subsequent storage, even at -79 {degrees}C. The inclusion of ligands, such as Thioflavin X, during aggregation affected both the reaction kinetics and the fibril morphologies formed. The addition of ligands to pre-formed fibrils also produced changes in fibril morphology. These results highlight that Syn fibrils are in equilibrium with their chemical environment and transition through a series of transient morphologies. Furthermore, these findings suggest the potential to use ligands to remodel fibril structure, possibly allowing for pathological morphologies to be converted to less pathological forms.

The transmembrane protein responsible for the electrogenic transport of Na+ and K+ across the plasma membrane, the Na+/K+-ATPase, highly vulnerable redox modulations and thiol modifying agents due to the presence of thiol groups at the nucleotide and cationic sites. However, reports have demonstrated a preferential interaction of these protein thiols with oxidizing agents. The reactivity of protein thiols is strongly linked with the nature of the microenvironment of these thiols, hence, the present study sought to experimentally elucidate key features of the microenvironment of the catalytically relevant thiols at the substrate-binding sites of this crucial enzyme. Two thiol modifiers with similar thiol-reactive mechanism, but different molecular properties, iodoacetamide (IA) and N-acetyl-4-phenyliodoacetamide (APIAM), were employed. It was observed that while both compounds demonstrated excellent thiol-oxidizing properties in the chemical model, only APIAM had an inhibitory effect on the activity of the Na+/K+-ATPase. The involvement of the catalytically relevant thiols at the nucleotide and cation-binding sites of the enzyme in APIAM-mediated inhibition was confirmed by the protective effect of preincubating the reaction system with dithiothreitol (DTT). The findings from this study suggest that the catalytically relevant thiols of this enzyme are likely buried in a hydrophobic microenvironment. This could be a part of the protective measure of nature for these vulnerable protein thiols. Further details from our findings can be explored in the therapeutic management of diseases for which a dysfunction in the Na+/K+-ATPase have been identified. HighlightsO_LIThe transmembrane Na+/K+-ATPase has well-defined substrate-binding domains exposed to both aqueous microenvironment and buried within the hydrophobic transmembrane microenvironment C_LIO_LIThese microenvironments influence vulnerability of the critical thiols of the enzyme to oxidative assault C_LIO_LIThese thiols are likely buried in the hydrophobic core of the enzyme, thus selecting its susceptibility to thiol modfying agents C_LI

Three copper(II) complexes containing 1,10-phenanthroline ([CuCl2(phen)]{middle dot}4H2O,1), neocuproine ([CuCl2(neo)]{middle dot}4H2O, 2) and tetramethyl-phenanthroline ([CuCl2(tmp)]{middle dot}4H2O, 3) as the primary ligand and another three copper(II) complexes with the L-Ala-Phe dipeptide as an auxiliary ligand: [Cu(L-Ala-Phe)(phen)]{middle dot}4H2O (4), [Cu(L-Ala-Phe)(neo)]{middle dot}4H2O (5) and [Cu(L-Ala-Phe)(tmp)]{middle dot}4H2O (6), inhibited cell viability in breast cancer MCF-7 cell line, both in the monolayer and spheroid cell culture models. The pair with tetramethyl-phenanthroline displayed a better selectivity index than cisPt and non-cytotoxicity-related ROS induction and apoptosis in the monolayer breast cancer model. Cell proliferation was affected by all compounds in a concentration-dependent manner, with a more substantial effect on the tetramethyl-phenanthroline complexes. Cell viability on multicellular spheroids showed a concentration-dependent reduction from 1 M, with IC50 that were half the one for cisplatin. All copper complexes, except for 1 showed DNA damage, demonstrated by the comet assay at a concentration below the IC50. The role of NHE1 has been linked to many types of cancers. Our study revealed that all compounds inhibited NHE1 activity in MCF-7 cells. However, only complexes containing the dipeptide auxiliary ligand could extend their effect on cell migration (Wound Healing Assay) and MMP-9 activity studied by zimography. Wester Blot analysis showed that expressions of MMP-2, MMP-9, and NHE1 were affected when MCF7 cells were treated with the six compounds as well. Overall, our results reveal an antitumor effect of all copper(II) complexes studied in breast cancer cells and a fundamental role of NHE1 in cell migration.

Mutational analysis of the cellular prion protein (PrPC) has revealed various regions of the protein that modulate prion propagation. However, most approaches involve deletions, insertions, or replacements in the presence of the wild-type cellular protein, which may mask the true phenotype. Here, site-directed alanine mutagenesis of PrPC was conducted to identify sites particularly a surface patch of the protein pertinent to prion propagation in the absence of the wild-type prion protein. Mutations were targeted to the helical, sheet and loop regions of PrPC, or a combination thereof and the mutated proteins expressed in PK1 cells in which endogenous PrPC had been silenced. PK1 cells are a clone of mouse neuroblastoma cells that are highly susceptible to Rocky Mountain Laboratory mouse prions. Using the scrapie cell assay, a highly sensitive cell culture-based bioassay for quantifying infectious titres of mouse prions, we found that all mutations within the structured 121-230 domain, irrespective of secondary structure, severely reduced prion propagation. The reduction was most pronounced for mutations within conformationally variable regions of the protein (G123A.L124A.G125A and V188A.T191A.T192A) and those neighbouring or within helix 1 (S134A.R135A.M153A and H139A.G141A.D146A). While mutations G123A and G125A would likely disrupt the structure of the prion fibril, the other mutations are unlikely to cause disruption. Our data therefore suggests that conformationally variable regions within the structured domain of PrPC are the major determinants of prion propagation efficacy.

With an increasing aging population, neurodegenerative diseases are having an increased impact on society. Typically, these diseases are diagnosed significantly past symptom onset, decreasing the possibility of effective treatment. A non-invasive biomarker and specific target are needed to diagnose and treat the disease before late-stage symptoms. GM1 Gangliosidosis is a lysosomal storage disease where lysosomal enzyme {beta}-galactosidase is missing. As a result, GM1 ganglioside is not broken down and accumulates in the cell, ultimately leading to cell death. One of the main aspects of GM1 Gangliosidosis, and other neurodegenerative diseases, is impaired autophagy: reduced fusion of autophagosomes and lysosomes to degrade cellular waste. In this paper, we show that healthy cells (NSV3) have approximately 13 times more co-localization of lysosomes and autophagosomes than GM1 Gangliosidosis-diseased cells (GM1SV3), as demonstrated via immunofluorescence. GM1SV3 fold normal enzyme activity of {beta}-galactosidase was downregulated while mannosidase, and hexosaminidase A were both upregulated. When inducing impaired autophagy in NSV3 via starvation, co-localization gradually decreases with increased starvation time. Most notably, after 48-hour starvation, healthy cells (NSV3) showed no significant difference in co-localization compared to GM1SV3. NSV3 under starvation conditions showed a significant increase between time starved and fold normal enzyme activity, with a positive correlation being observed. Activities of mannosidase, and hexosaminidase A of starved NSV3 closely resemble, and surpass, GM1SV3 after 12-hour starvation. These observations have the potential to expand the conversation regarding impaired autophagy as a potential biomarker for disease progression and diagnostics and as a treatment target.

Membrane binding and aggregation properties of -synuclein are closely associated with Parkinsons disease and a class of related syndromes named as synucleinopathy. This study explored the potential of SS-31 (Elamipretide), a therapeutic tetrapeptide with alternating cationic and aromatic residues and known properties of mitochondrial inner membrane binding and oxidative stress reduction, in modulating -synuclein interaction with the lipid membranes and mitigating impairment of mitochondrial function induced by -synuclein oligomers. It was demonstrated by both fluorescence correlation spectroscopy and fluorescence anisotropy that SS-31 displaces both wild-type and N-terminus acetylated -synuclein from negatively charged small unilamellar vesicles in a dose-dependent manner. Thioflavin-T assay and transmission electron microscopy (TEM) showed that SS-31 inhibits membrane-induced -synuclein aggregation and alters the morphology of -synuclein fibrils. Moreover, Seahorse Mito Stress Test indicated that SS-31 restores impaired mitochondrial function in -synuclein oligomer-treated neuroblastoma cells. Finally, confocal imaging revealed that SS-31 hinders cellular uptake of -synuclein oligomers, possibly by modifying cell membrane electrostatics. These findings underscore the multifaceted protective role of SS-31 against mitochondrial dysfunction caused by -synuclein aggregation. Consequently, SS-31 emerges as a promising therapeutic candidate to attenuate neurodegeneration pertinent to -synuclein misfolding and aggregation. There is a good potential for further refinement of such peptide against many diseases linked to mitochondrial dysfunction and oxidative stress.

Two alternative architectures have been proposed for PrPSc, the most notorious prion: a parallel in register {beta} stack (PIRIBS) and a 4-rung {beta}-solenoid (4R{beta}S). We challenged these two models by measuring intermolecular 13C-13C dipole-dipole couplings of 13CO-labelled Phe residues in a fully infectious sample of recombinant bank vole PrPSc (recBVPrPSc) using a PITHIRDS-CT solid state NMR (ssNMR) experiment. To our surprise, data strongly support a PIRIBS architecture. However, the mean distance measured ([~]6.5 [A]) suggests that a minimum of two of the three Phe residues are not perfectly stacked at the canonical [~]5 [A] cross-{beta} distance. Additional ssNMR experiments show some local conformational variability of the Phe residues within limits of a relatively high rigidity. The most parsimonious interpretation of our data is that recBVPrPSc is arranged as a PIRIBS, although additional conformers with alternative architectures cannot be excluded, including a mixture of PIRIBS and 4R{beta}S. Author summaryPrPSc is the most notorious prion. It is an infectious protein that cuases fatal neurodegenerative diseases in humans and animals. PrPSc is the aberrant version of a brain protein, PrPC. PrPSc and PrPC have the same prinary structure, but different secondary, tertiaty and quaternary structures. PrPSc is capable of templating PrPC to convert to the PrPSc conformation, which is the basis of its capacity to propagate. Two plausible structural models of PrPSc have been proposed, the four-rung {beta}-solenoid (4R{beta}S) and the parallel in-register {beta} stack (PIRIBS) model. In both cases the driving force of the templating mechanism consists of "sticky" surface {beta}-strands; however, in the PIRIBS model all the {beta}-strands that conform a PrPSc monomer lie flat on a surface whereas in the 4R{beta}S model they wind in a corkscrew fashion. Here, we analyzed fully infectious recombinant PrPSc using a solid state NMR technique, PITHIRDS, that allows probing distances between specific labelled amino acid residues. To our surprise (as we have defended the 4R{beta}S model in the past), results clearly show the presence of a PIRIBS structure in our sample.

Tau undergoes fibrillogenesis in a group of neurodegenerative diseases termed tauopathies. Each tauopathy is characterized by tau fibrils with disease-specific conformations, highlighting the complexity of tau self-assembly. This has led to debate surrounding the precise mechanisms that govern the self-assembly of tau in disease, especially the involvement of disulphide bonding (DSB) between cysteine residues. In this study, we use a truncated form of tau, dGAE, capable of forming filaments identical to those in disease. We reveal the impact of DSB in dGAE assembly and propagation by resolving the global mechanisms that dominate its assembly. We found evidence for surface-mediated secondary nucleation and fragmentation being active in dGAE assembly. The inhibition of DSB during dGAE assembly leads to an enhanced aggregation rate through a reduced lag phase, but with no effect on the global assembly mechanisms. We suggest this is due to the formation a dominant, seed-competent species in the absence of DSB that facilitates elongation and secondary nucleation resulting in enhanced assembly. In vitro seeding assays reveal the recruitment of endogenous tau in a cell model only when using dGAE species formed under conditions that inhibit DSB. Our results further support the use of the in vitro dGAE tau aggregation model for investigating the mechanism of tau assembly, the effect of varying conditions on tau assembly and how these conditions affect the resultant species. Further studies may utilise dGAE and its aggregates to investigate tau seeding, propagation and to highlight or test potential targets for therapies that reduce the spread of pathologic tau throughout the brain.

Cu/Zn superoxide dismutase 1 (SOD1) is essential for maintaining neural health. Its functions include modulating metabolism, maintaining redox balance, regulating transcription, besides eliminating superoxide radicals, which are achieved through various post-translational modifications (PTMs). Consequently, unusual PTMs in SOD1 can impair its functionality and stability, leading to the accumulation of misfolded SOD1 and the increase of oxidative stress markers, hallmarks of Amyotrophic Lateral Sclerosis (ALS). Although SOD1 has been extensively studied, especially regarding its role in ALS, relatively little is known about how aging and mutations affect SOD1 PTMs. This study aimed to evaluate the effect of oxidative stress induced by chronological aging on PTMs of human SOD1: wild-type (WT) and A5V SOD1, a severe ALS-related mutant. To do this, both hSOD1 forms were expressed in Saccharomyces cerevisiae lacking the SOD1 gene, and then purified from extracts of stressed and non-stressed cells. PTMs were analyzed using mass spectrometry, observing the modification of WT and mutant human SOD1 in both conditions. We observed changes in the levels of damage, including oxidation, formylation, and carboxylation, such as oxidized tryptophan 33, associated with prion-like propagation of SOD1 misfolding. Increased levels of this PTM appeared in WT SOD1 after aging and in A5V SOD1. Acetylation and succinylation were also found on lysines. Some of these modifications already have described functions in the literature, while others still lack a defined role. Interestingly, the levels of these physiological PTMs differed between WT and mutant SOD1, providing important information for elucidating the molecular mechanisms of ALS involving SOD1.

Neutrophil extracellular traps (NETs) are chromatin-derived structures decorated with neutrophil enzymes such as elastase and myeloperoxidase. Our group has previously demonstrated that amyloid fibrils (AFs), regardless of their protein composition, induce NET release in vitro in human neutrophils through a process dependent on reactive oxygen species (ROS) generation by NADPH oxidase 2 (NOX-2). Moreover, the proteases embedded in NETs were shown to degrade AFs into smaller, potentially toxic species. The present study aimed to determine whether amyloid fibrils composed of -synuclein (SF) can induce NET formation in vivo and to investigate the role of NETs in modulating amyloid-associated pathology. To this end, we employed gp91phox knockout (KO) mice, which lack NOX-2 activity and are therefore unable to release NETs. SF was instilled into the lungs of both WT and KO mice (males and females), leveraging the lungs robust immune cell recruitment - particularly of neutrophils-as a model system. Eight hours after SF instillation, both WT and KO animals exhibited marked neutrophil infiltration in the lungs causing inflammation. However, NET formation-evidenced by the presence of citrullinated histones and myeloperoxidase - was detected only in WT mice. Interestingly, while Congo red-positive amyloid-like structures persisted in the lungs of KO mice, they were absent in the lungs of WT animals, suggesting that NET-associated proteases facilitate the clearance of AFs from lung tissue. Lung function was assessed by measuring elastance and resistance. Our data showed that, while AFs were still present in the lungs of both WT and KO mice, elastance was impaired. As AFs were cleared from the lungs of WT mice, lung function recovered. In contrast, KO animals, in which AFs persisted, continued to exhibit compromised elastance. Together, our findings demonstrate that AFs impair lung function, and that NETs, induced in response to these fibrils, promote their degradation and thereby protect lung tissue from further damage.

Cytochrome c552 from Wolinella succinogenes is one of the few examples of a low reduction potential class I c-type cytochrome with a mixture of high/low spin state populations observed in its visible spectrum. Analysis of its structural model suggests that the heme is Met/His coordinated and highly solvent-exposed. This supports the hypothesis that it is the solvent accessibility of the propionate groups that controls the reduction potential of small c-type cytochromes. The visible spectra obtained at different pH values reveal the presence of a protonable group with a pKa of 7.3, which also influences the reduction potential of this small cytochrome c552 (Em0 of 97 {+/-} 5 mV, pH 7.0) and can be either an H2O/OH- group distantly coordinating the heme iron, or one of the propionate groups. The thermostability of cytochrome c552 has been studied by circular dichroism and differential scanning calorimetry, indicating a highly stable protein at pH 5-7 (90 {degrees}C to 77 {degrees}C).