Arresting amyloid with coulomb's law: acetylation of ALS-linked SOD1 by aspirin impedes aggregation

Variability in SOD1-associated amyotrophic lateral sclerosis: geographic patterns, clinical heterogeneity, molecular alterations, and therapeutic implications

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of motor neurons, resulting in global health burden and limited post-diagnosis life expectancy. Although primarily sporadic, familial ALS (fALS) cases suggest a genetic basis. This review focuses on SOD1, the first gene found to be associated with fALS, which has been more recently confirmed by genome sequencing. While informative, databases such as ALSoD and STRENGTH exhibit regional biases. Through a systematic global examination of SOD1 mutations from 1993 to 2023, we found different geographic distributions and clinical presentations. Even though different SOD1 variants are expressed at different protein levels and have different half-lives and dismutase activities, these alterations lead to loss of function that is not consistently correlated with disease severity. Gain of function of toxic aggregates of SOD1 resulting from mutated SOD1 has emerged as one of the key contributors to ALS. Therapeutic interventions specifically targeting toxic gain of function of mutant SOD1, including RNA interference and antibodies, show promise, but a cure remains elusive. This review provides a comprehensive perspective on SOD1-associated ALS and describes molecular features and the complex genetic landscape of SOD1, highlighting its importance in determining diverse clinical manifestations observed in ALS patients and emphasizing the need for personalized therapeutic strategies.

Abnormal protein post-translational modifications induces aggregation and abnormal deposition of protein, mediating neurodegenerative diseases

Protein post-translational modifications (PPTMs) refer to a series of chemical modifications that occur after the synthesis of protein. Proteins undergo different modifications such as phosphorylation, acetylation, ubiquitination, and so on. These modifications can alter the protein's structure, function, and interaction, thereby regulating its biological activity. In neurodegenerative diseases, several proteins undergo abnormal post-translational modifications, which leads to aggregation and abnormal deposition of protein, thus resulting in neuronal death and related diseases. For example, the main pathological features of Alzheimer's disease are the aggregation of beta-amyloid protein and abnormal phosphorylation of tau protein. The abnormal ubiquitination and loss of α-synuclein are related to the onset of Parkinson's disease. Other neurodegenerative diseases such as Huntington's disease, amyotrophic lateral sclerosis, and so on are also connected with abnormal PPTMs. Therefore, studying the abnormal PPTMs in neurodegenerative diseases is critical for understanding the mechanism of these diseases and the development of significant therapeutic strategies. This work reviews the implications of PPTMs in neurodegenerative diseases and discusses the relevant therapeutic strategies.

Site Identification by Ligand Competitive Saturation-Biologics Approach for Structure-Based Protein Charge Prediction

Protein-based therapeutics typically require high concentrations of the active protein, which can lead to protein aggregation and high solution viscosity. Such solution behaviors can limit the stability, bioavailability, and manufacturability of protein-based therapeutics and are directly influenced by the charge of a protein. Protein charge is a system property affected by its environment, including the buffer composition, pH, and temperature. Thus, the charge calculated by summing the charges of each residue in a protein, as is commonly done in computational methods, may significantly differ from the effective charge of the protein as these calculations do not account for contributions from bound ions. Here, we present an extension of the structure-based approach termed site identification by ligand competitive saturation-biologics (SILCS-Biologics) to predict the effective charge of proteins. The SILCS-Biologics approach was applied on a range of protein targets in different salt environments for which membrane-confined electrophoresis-determined charges were previously reported. SILCS-Biologics maps the 3D distribution and predicted occupancy of ions, buffer molecules, and excipient molecules bound to the protein surface in a given salt environment. Using this information, the effective charge of the protein is predicted such that the concentrations of the ions and the presence of excipients or buffers are accounted for. Additionally, SILCS-Biologics also produces 3D structures of the binding sites of ions on the proteins, which enable further analyses such as the characterization of protein surface charge distribution and dipole moments in different environments. Notable is the capability of the method to account for competition between salts, excipients, and buffers on the calculated electrostatic properties in different protein formulations. Our study demonstrates the ability of the SILCS-Biologics approach to predict the effective charge of proteins and its applicability in uncovering protein-ion interactions and their contributions to protein solubility and function.

Electrostatic interactions mediate the nucleation and growth of a bacterial functional amyloid

Bacterial biofilm formation can have severe impacts on human and environmental health. Enteric bacteria produce functional amyloid fibers called curli that aid in biofilm formation and host colonization. CsgA is the major proteinaceous component of curli amyloid fibers and is conserved in many gram-negative enteric bacteria. The CsgA amyloid core consists of five imperfect repeats (R1-R5). R2, R3, and R4 have aspartic acid (D) and glycine (G) residues that serve as "gatekeeper" residues by modulating the intrinsic aggregation propensity of CsgA. Here, using mutagenesis, salt-mediated charge screening, and by varying pH conditions, we show that the ability of CsgA variants to nucleate and form amyloid fibers is dictated by the charge state of the gatekeeper residues. We report that in Citrobacter youngae CsgA, certain arginine (R) and lysine (K) residues also act as gatekeeper residues. A mechanism of gatekeeping is proposed wherein R and K residues electrostatically interact with negatively charged D residues, tempering CsgA fiber formation.

A method for quantifying how the activity of an enzyme is affected by the net charge of its nearest crowded neighbor

The electrostatic effects of protein crowding have not been systematically explored. Rather, protein crowding is generally studied with co‐solvents or crowders that are electrostatically neutral, with no methods to measure how the net charge (Z) of a crowder affects protein function. For example, can the activity of an enzyme be affected electrostatically by the net charge of its neighbor in crowded milieu? This paper reports a method for crowding proteins of different net charge to an enzyme via semi‐random chemical crosslinking. As a proof of concept, RNase A was crowded (at distances ≤ the Debye length) via crosslinking to different heme proteins with Z = +8.50 ± 0.04, Z = +6.39 ± 0.12, or Z = −10.30 ± 1.32. Crosslinking did not disrupt the structure of proteins, according to amide H/D exchange, and did not inhibit RNase A activity. For RNase A, we found that the electrostatic environment of each crowded neighbor had significant effects on rates of RNA hydrolysis. Crowding with cationic cytochrome c led to increases in activity, while crowding with anionic “supercharged” cytochrome c or myoglobin diminished activity. Surprisingly, electrostatic crowding effects were amplified at high ionic strength (I = 0.201 M) and attenuated at low ionic strength (I = 0.011 M). This salt dependence might be caused by a unique set of electric double layers at the dimer interspace (maximum distance of 8 Å, which cannot accommodate four layers). This new method of crowding via crosslinking can be used to search for electrostatic effects in protein crowding.

Altered SOD1 maturation and post-translational modification in amyotrophic lateral sclerosis spinal cord

Aberrant self-assembly and toxicity of wild-type and mutant superoxide dismutase 1 (SOD1) has been widely examined in silico, in vitro, and in transgenic animal models of amyotrophic lateral sclerosis (ALS). Detailed examination of the protein in disease-affected tissues from ALS patients, however, remains scarce. We employed histological, biochemical and analytical techniques to profile alterations to SOD1 protein deposition, subcellular localization, maturation and post-translational modification in post-mortem spinal cord tissues from ALS cases and controls. Tissues were dissected into ventral and dorsal spinal cord grey matter to assess the specificity of alterations within regions of motor neuron degeneration. We provide evidence of the mislocalization and accumulation of structurally-disordered, immature SOD1 protein conformers in spinal cord motor neurons of SOD1-linked and non-SOD1-linked familial ALS cases, and sporadic ALS cases, compared with control motor neurons. These changes were collectively associated with instability and mismetallation of enzymatically-active SOD1 dimers, as well as alterations to SOD1 post-translational modifications and molecular chaperones governing SOD1 maturation. Atypical changes to SOD1 protein were largely restricted to regions of neurodegeneration in ALS cases, and clearly differentiated all forms of ALS from controls. Substantial heterogeneity in the presence of these changes was also observed between ALS cases. Our data demonstrates that varying forms of SOD1 proteinopathy are a common feature of all forms of ALS, and support the presence of one or more convergent biochemical pathways leading to SOD1 proteinopathy in ALS. The majority of these alterations are specific to regions of neurodegeneration, and may therefore constitute valid targets for therapeutic development.

Clinical Applications of Aspirin as a Multi-potent Drug Beyond Cardiovascular Implications: A Proof of Concept for Anesthesiologists- A Narrative Review

To the best of our knowledge, aspirin (ASA) is known as a commonly used medication worldwide. Although the cardiovascular aspects of ASA are well-established, recently, it has been identified that ASA can yield multiple extra-cardiovascular therapeutic potencies in facing neurodegenerative disorders, various cancers, inflammatory responses, and the COVID-19 pandemic. In this review, we aimed to highlight the proven role of ASA administration in the variety of non-cardiovascular diseases, particularly in the field of anesthesiology.

Supercharging Prions via Amyloid-Selective Lysine Acetylation

Repulsive electrostatic forces between prion-like proteins are a barrier against aggregation. In neuropharmacology, however, a prion's net charge (Z) is not a targeted parameter. Compounds that selectively boost prion Z remain unreported. Here, we synthesized compounds that amplified the negative charge of misfolded superoxide dismutase-1 (SOD1) by acetylating lysine-NH₃ ⁺ in amyloid-SOD1, without acetylating native-SOD1. Compounds resembled a "ball and chain" mace: a rigid amyloid-binding "handle" (benzothiazole, stilbene, or styrylpyridine); an aryl ester "ball"; and a triethylene glycol chain connecting ball to handle. At stoichiometric excess, compounds acetylated up to 9 of 11 lysine per misfolded subunit (ΔZ_fibril =-8100 per 10³ subunits). Acetylated amyloid-SOD1 seeded aggregation more slowly than unacetylated amyloid-SOD1 in vitro and organotypic spinal cord (these effects were partially due to compound binding). Compounds exhibited reactivity with other amyloid and non-amyloid proteins (e.g., fibrillar α-synuclein was peracetylated; serum albumin was partially acetylated; carbonic anhydrase was largely unacetylated).

Amyotrophic Lateral Sclerosis: Proteins, Proteostasis, Prions, and Promises

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of the motor neurons that innervate muscle, resulting in gradual paralysis and culminating in the inability to breathe or swallow. This neuronal degeneration occurs in a spatiotemporal manner from a point of onset in the central nervous system (CNS), suggesting that there is a molecule that spreads from cell-to-cell. There is strong evidence that the onset and progression of ALS pathology is a consequence of protein misfolding and aggregation. In line with this, a hallmark pathology of ALS is protein deposition and inclusion formation within motor neurons and surrounding glia of the proteins TAR DNA-binding protein 43, superoxide dismutase-1, or fused in sarcoma. Collectively, the observed protein aggregation, in conjunction with the spatiotemporal spread of symptoms, strongly suggests a prion-like propagation of protein aggregation occurs in ALS. In this review, we discuss the role of protein aggregation in ALS concerning protein homeostasis (proteostasis) mechanisms and prion-like propagation. Furthermore, we examine the experimental models used to investigate these processes, including in vitro assays, cultured cells, invertebrate models, and murine models. Finally, we evaluate the therapeutics that may best prevent the onset or spread of pathology in ALS and discuss what lies on the horizon for treating this currently incurable disease.

Regulation of Functional Protein Aggregation by Multiple Factors: Implications for the Amyloidogenic Behavior of the CAP Superfamily Proteins

The idea that amyloid fibrils and other types of protein aggregates are toxic for cells has been challenged by the discovery of a variety of functional aggregates. However, an identification of crucial differences between pathological and functional aggregation remains to be explored. Functional protein aggregation is often reversible by nature in order to respond properly to changing physiological conditions of the cell. In addition, increasing evidence indicates that fast fibril growth is a feature of functional amyloids, providing protection against the long-term existence of potentially toxic oligomeric intermediates. It is becoming clear that functional protein aggregation is a complexly organized process that can be mediated by a multitude of biomolecular factors. In this overview, we discuss the roles of diverse biomolecules, such as lipids/membranes, glycosaminoglycans, nucleic acids and metal ions, in regulating functional protein aggregation. Our studies on the protein GAPR-1 revealed that several of these factors influence the amyloidogenic properties of this protein. These observations suggest that GAPR-1, as well as the cysteine-rich secretory proteins, antigen 5 and pathogenesis-related proteins group 1 (CAP) superfamily of proteins that it belongs to, require the assembly into an amyloid state to exert several of their functions. A better understanding of functional aggregate formation may also help in the prevention and treatment of amyloid-related diseases.

Lipid aldehyde hydrophobicity affects apo-SOD1 modification and aggregation

Unsaturated lipids are oxidized by reactive oxygen species and enzymes, leading to the increased formation of lipid hydroperoxides and several electrophilic products. Lipid-derived electrophiles can modify macromolecules, such as proteins, resulting in the loss of function and/or aggregation. The accumulation of Cu,Zn-superoxide dismutase (SOD1) aggregates has been associated with familial cases of amyotrophic lateral sclerosis (ALS). The protein aggregation mechanisms in motor neurons remain unclear, although recent studies have shown that lipids and oxidized lipid derivatives may play roles in this process. Here, we aimed to compare the effects of different lipid aldehydes on the induction of SOD1 modifications and aggregation, in vitro. Human recombinant apo-SOD1 was incubated with 4-hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE), 2-hexen-1-al (HEX), 2,4-nonadienal (NON), 2,4-decadienal (DEC), or secosterol aldehydes (SECO-A or SECO-B). High-molecular-weight apo-SOD1 aggregates dramatically increased in the presence of highly hydrophobic aldehydes (LogP_calc > 3). Notably, several Lys residues were modified by exposure to all aldehydes. The observed modifications were primarily observed on Lys residues located near the dimer interface (K3 and K9) and at the electrostatic loop (K122, K128, and K136). Moreover, HHE and HNE induced extensive apo-SOD1 modifications, by forming Schiff bases or Michael adducts with Lys, His, and Cys residues. However, these aldehydes were unable to induce large protein aggregates. Overall, our data shed light on the importance of lipid aldehyde hydrophobicity on the induction of apo-SOD1 aggregation and identified preferential sites of lipid aldehyde-induced modifications.

Analyzing structural alterations of mitochondrial intermembrane space superoxide scavengers cytochrome-c and SOD1 after methylglyoxal treatment

Mitochondria are quantitatively the most important sources of reactive oxygen species (ROS) which are formed as by-products during cellular respiration. ROS generation occurs when single electrons are transferred to molecular oxygen. This leads to a number of different ROS types, among them superoxide. Although most studies focus on ROS generation in the mitochondrial matrix, the intermembrane space (IMS) is also important in this regard. The main scavengers for the detoxification of superoxide in the IMS are Cu, Zn superoxide dismutase (SOD1) and cytochrome-c. Similar to ROS, certain reactive carbonyl species are known for their high reactivity. The consequences are deleterious modifications to essential components compromising cellular functions and contributing to the etiology of severe pathological conditions like cancer, diabetes and neurodegeneration. In this study, we investigated the susceptibility of SOD1 and cytochrome-c to in vitro glycation by the dicarbonyl methylglyoxal (MGO) and the resulting effects on their structure. We utilized experimental techniques like immunodetection of the MGO-mediated modification 5-hydro-5-methylimidazolone, differential scanning calorimetry, fluorescence emission and circular dichroism measurements. We found that glycation of cytochrome-c leads to monomer aggregation, an altered secondary structure (increase in alpha helical content) and slightly more compact folding. In addition to structural changes, glycated cytochrome-c displays an altered thermal unfolding behavior. Subjecting SOD1 to MGO does not influence its secondary structure. However, similar to cytochrome-c, subunit aggregation is observed under denaturating conditions. Furthermore, the appearance of a second peak in the calorimetry diagram indirectly suggests de-metallation of SOD1 when high MGO levels are used. In conclusion, our data demonstrate that MGO has the potential to alter several structural parameters in important proteins of energy metabolism (cytochrome-c) and antioxidant defense (cytochrome-c, SOD1).

Kinetic Variability in Seeded Formation of ALS-Linked SOD1 Fibrils Across Multiple Generations

The unseeded aggregation of superoxide dismutase-1 (SOD1) into amyloid-like fibrils occurs stochastically in vitro and in vivo, that is, isolated populations of SOD1 proteins (within microplate wells or living cells) self-assemble into amyloid at rates that span a probability distribution. This stochasticity has been attributed to variable degrees of monomer depletion by competing pathways of amorphous and fibrillar aggregation (inter alia). Here, microplate-based thioflavin-T (ThT) fluorescence assays were performed at high iteration (∼300) to establish whether this observed stochasticity persists when progenitor ("parent") SOD1 fibrils are used to seed the formation of multiple generations of progeny fibrils (daughter, granddaughter, and great-granddaughter fibrils). Populations of progenitor fibrils formed stochastically at different rates and fluorescence intensity, however, progeny fibrils formed at more similar rates regardless of the formation rate of the progenitor fibril. For example, populations of progenitor fibrils that formed with a lag time of ∼30 h or ∼15 h both produced progeny fibrils with lag times of ∼8 h. Likewise, populations of progenitor fibrils with high or low maximum fluorescence (e.g., ∼450 or ∼75 A.U.) both produced progeny fibrils with more similar maximum fluorescence (∼125 A.U.). The rate of propagation was found to be more dependent on monomer concentration than seed concentration. These results can be rationalized by classical rate laws for primary nucleation and monomer-dependent secondary nucleation. We also find that the seeding propensity of some "families" of in vitro grown fibrils exhibit a finite lifetime (similar to that observed in the seeding of small molecule crystals and colloids). The single biological takeaway of this study is that the concentration of native SOD1 in a cell can have a stronger effect on rates of seeded aggregation than the concentration of prion-like seed that infected the cell.

Tryptophan residue 32 in human Cu-Zn superoxide dismutase modulates prion-like propagation and strain selection

Mutations in Cu/Zn superoxide dismutase 1 (SOD1) associated with familial amyotrophic lateral sclerosis cause the protein to aggregate via a prion-like process in which soluble molecules are recruited to aggregates by conformational templating. These misfolded SOD1 proteins can propagate aggregation-inducing conformations across cellular membranes. Prior studies demonstrated that mutation of a Trp (W) residue at position 32 to Ser (S) suppresses the propagation of misfolded conformations between cells, whereas other studies have shown that mutation of Trp 32 to Phe (F), or Cys 111 to Ser, can act in cis to attenuate aggregation of mutant SOD1. By expressing mutant SOD1 fused with yellow fluorescent protein (YFP), we compared the relative ability of these mutations to modulate the formation of inclusions by ALS-mutant SOD1 (G93A and G85R). Only mutation of Trp 32 to Ser persistently reduced the formation of the amorphous inclusions that form in these cells, consistent with the idea that a Ser at position 32 inhibits templated propagation of aggregation prone conformations. To further test this idea, we produced aggregated fibrils of recombinant SOD1-W32S in vitro and injected them into the spinal cords of newborn mice expressing G85R-SOD1: YFP. The injected mice developed an earlier onset paralysis with a frequency similar to mice injected with WT SOD1 fibrils, generating a strain of misfolded SOD1 that produced highly fibrillar inclusion pathology. These findings suggest that the effect of Trp 32 in modulating the propagation of misfolded SOD1 conformations may be dependent upon the “strain” of the conformer that is propagating.

Aspirin Reshapes Acetylomes in Inflammatory and Cancer Cells via CoA-Dependent and CoA-Independent Pathways

Aspirin, or acetylsalicylic acid (ASA), is the most widely used medication to relieve pain, fever, and inflammation. Recent studies have revealed new benefits of aspirin, including reduction of heart attack and stroke, anticancer, and life extension. Despite the profound effects of aspirin, the mechanism of its action remains to be elucidated. Here, we used deuterium-labeled aspirin (D-aspirin) together with mass spectrometry-based acetylomic analysis, termed DAcMS, to investigate the landscape of protein acetylation induced by aspirin. The DAcMS revealed the acetylomes of lipopolysaccharide-induced inflammatory BV2 cells and colon cancer HCT116 cells. The acetylation level was substantially induced upon aspirin treatment in both cell lines. In total, we identified 17,003 acetylation sites on 4623 proteins in BV2 cells and 16,366 acetylated sites corresponding to 4702 acetylated proteins in HCT116 cells. Importantly, functional analyses of these aspirin-induced acetylated proteins suggested that they were highly enriched in many key biological categories, which function importantly in inflammatory response. We further demonstrated that aspirin acetylates proteins through both acetyl-CoA-dependent and acetyl-CoA-independent pathways, and the accessible lysine residues at the protein surface are major acetylation targets of aspirin. Hence, our study provides the comprehensive atlas of aspirin-induced acetylome under disease conditions. This knowledge proffers new insight into the aspirin-directed acetylome and perhaps new drug target sites relevant to human cancer and inflammatory diseases. The MS data of this study have been deposited under the accession number IPX0001923000 at iProX.

Acetylation of Aβ40 Alters Aggregation in the Presence and Absence of Lipid Membranes

A hallmark of Alzheimer's disease (AD) is the formation of senile plaques comprised of the β-amyloid (Aβ) peptide. Aβ fibrillization is a complex nucleation-dependent process involving a variety of metastable intermediate aggregates and features the formation of inter- and intramolecular salt bridges involving lysine residues, K16 and K28. Cationic lysine residues also mediate protein-lipid interactions via association with anionic lipid headgroups. As several toxic mechanisms attributed to Aβ involve membrane interactions, the impact of acetylation on Aβ₄₀ aggregation in the presence and absence of membranes was determined. Using chemical acetylation, varying mixtures of acetylated and nonacetylated Aβ₄₀ were produced. With increasing acetylation, fibril and oligomer formation decreased, eventually completely arresting fibrillization. In the presence of total brain lipid extract (TBLE) vesicles, acetylation reduced the interaction of Aβ₄₀ with membranes; however, fibrils still formed at near complete levels of acetylation. Additionally, the combination of TBLE and acetylated Aβ promoted annular aggregates. Finally, toxicity associated with Aβ₄₀ was reduced with increasing acetylation in a cell culture assay. These results suggest that in the absence of membranes that the cationic character of lysine plays a major role in fibril formation. However, acetylation promotes unique aggregation pathways in the presence of lipid membranes.

Structural Insights Into TDP-43 and Effects of Post-translational Modifications

Transactive response DNA binding protein (TDP-43) is a key player in neurodegenerative diseases. In this review, we have gathered and presented structural information on the different regions of TDP-43 with high resolution structures available. A thorough understanding of TDP-43 structure, effect of modifications, aggregation and sites of localization is necessary as we develop therapeutic strategies targeting TDP-43 for neurodegenerative diseases. We discuss how different domains as well as post-translational modification may influence TDP-43 overall structure, aggregation and droplet formation. The primary aim of the review is to utilize structural insights as we develop an understanding of the deleterious behavior of TDP-43 and highlight locations of established and proposed post-translation modifications. TDP-43 structure and effect on localization is paralleled by many RNA-binding proteins and this review serves as an example of how structure may be modulated by numerous compounding elements.

The biophysics of superoxide dismutase-1 and amyotrophic lateral sclerosis

Few proteins have come under such intense scrutiny as superoxide dismutase-1 (SOD1). For almost a century, scientists have dissected its form, function and then later its malfunction in the neurodegenerative disease amyotrophic lateral sclerosis (ALS). We now know SOD1 is a zinc and copper metalloenzyme that clears superoxide as part of our antioxidant defence and respiratory regulation systems. The possibility of reduced structural integrity was suggested by the first crystal structures of human SOD1 even before deleterious mutations in the sod1 gene were linked to the ALS. This concept evolved in the intervening years as an impressive array of biophysical studies examined the characteristics of mutant SOD1 in great detail. We now recognise how ALS-related mutations perturb the SOD1 maturation processes, reduce its ability to fold and reduce its thermal stability and half-life. Mutant SOD1 is therefore predisposed to monomerisation, non-canonical self-interactions, the formation of small misfolded oligomers and ultimately accumulation in the tell-tale insoluble inclusions found within the neurons of ALS patients. We have also seen that several post-translational modifications could push wild-type SOD1 down this toxic pathway. Recently we have come to view ALS as a prion-like disease where both the symptoms, and indeed SOD1 misfolding itself, are transmitted to neighbouring cells. This raises the possibility of intervention after the initial disease presentation. Several small-molecule and biologic-based strategies have been devised which directly target the SOD1 molecule to change the behaviour thought to be responsible for ALS. Here we provide a comprehensive review of the many biophysical advances that sculpted our view of SOD1 biology and the recent work that aims to apply this knowledge for therapeutic outcomes in ALS.

Species-specific consequences of an E40K missense mutation in superoxide dismutase 1 (SOD1)

A glutamic acid to lysine (E40K) residue substitution in superoxide dismutase 1 (SOD1) is associated with canine degenerative myelopathy: the only naturally occurring large animal model of amyotrophic lateral sclerosis (ALS). The E40 residue is highly conserved across mammals, except the horse, which naturally carries the (dog mutant) K40 residue. Here we hypothesized that in vitro expression of mutant dog SOD1 would recapitulate features of human ALS (ie, SOD1 protein aggregation, reduced cell viability, perturbations in mitochondrial morphology and membrane potential, reduced ATP production, and increased superoxide ion levels); further, we hypothesized that an equivalent equine SOD1 variant would share similar perturbations in vitro, thereby explain horses' susceptibility to certain neurodegenerative diseases. As in human ALS, expression of mutant dog SOD1 was associated with statistically significant increased aggregate formation, raised superoxide levels (ROS), and altered mitochondrial morphology (increased branching (form factor)), when compared to wild-type dog SOD1-expressing cells. Similar deficits were not detected in cells expressing the equivalent horse SOD1 variant. Our data helps explain the ALS-associated cellular phenotype of dogs expressing the mutant SOD1 protein and reveals that species-specific sequence conservation does not necessarily predict pathogenicity. The work improves understanding of the etiopathogenesis of canine degenerative myelopathy.

Mechanisms of SOD1 regulation by post-translational modifications

SOD1 is commonly known for its ROS scavenging activity, but recent work has uncovered additional roles in modulating metabolism, maintaining redox balance, and regulating transcription. This new paradigm of expanded SOD1 function raises questions regarding the regulation of SOD1 and the cellular partitioning of its biological roles. Despite decades of research on SOD1, much of which focuses on its pathogenic role in amyotrophic lateral sclerosis, relatively little is known about its regulation by post-translational modifications (PTMs). However, over the last decade, advancements in mass spectrometry have led to a boom in PTM discovery across the proteome, which has also revealed new mechanisms of SOD1 regulation by PTMs and an array of SOD1 PTMs with high likelihood of biological function. In this review, we address emerging mechanisms of SOD1 regulation by post-translational modifications, many of which begin to shed light on how the various functions of SOD1 are regulated within the cell.

SOD1 in amyotrophic lateral sclerosis development - in silico analysis and molecular dynamics of A4F and A4V variants

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that is characterized by the selective loss of motor neurons. Approximately 5% to 10% of patients with ALS have a family history of the disease, and approximately 20% of familial amyotrophic lateral sclerosis (fALS) cases are associated with mutations in Cu/Zn superoxide dismutase (SOD1). In this study, we evaluated the structural and functional effects of human A4F and A4V SOD1 protein mutations. We performed an in silico analysis using prediction algorithms of nonsynonymous single-nucleotide polymorphisms (nsSNPs) associated with the fALS development. Our structural conservation results show that the mutations analyzed (A4V and A4F) were in a highly conserved region. Molecular dynamics simulations using the Linux GROMACS package revealed how these mutations affect protein structure, protein stability, and aggregation. These results suggest that there might be an effect on the SOD1 function. Understanding the molecular basis of disease provides new insights useful for rational drug design and advancing our understanding of the ALS development.

What Are We Missing by Not Measuring the Net Charge of Proteins?

The net electrostatic charge (Z) of a folded protein in solution represents a bird's eye view of its surface potentials-including contributions from tightly bound metal, solvent, buffer, and cosolvent ions-and remains one of its most enigmatic properties. Few tools are available to the average biochemist to rapidly and accurately measure Z at pH≠pI. Tools that have been developed more recently seem to go unnoticed. Most scientists are content with this void and estimate the net charge of a protein from its amino acid sequence, using textbook values of pK_a . Thus, Z remains unmeasured for nearly all folded proteins at pH≠pI. When marveling at all that has been learned from accurately measuring the other fundamental property of a protein-its mass-one wonders: what are we missing by not measuring the net charge of folded, solvated proteins? A few big questions immediately emerge in bioinorganic chemistry. When a single electron is transferred to a metalloprotein, does the net charge of the protein change by approximately one elementary unit of charge or does charge regulation dominate, that is, do the pK_a values of most ionizable residues (or just a few residues) adjust in response to (or in concert with) electron transfer? Would the free energy of charge regulation (ΔΔG_z ) account for most of the outer sphere reorganization energy associated with electron transfer? Or would ΔΔG_z contribute more to the redox potential? And what about metal binding itself? When an apo-metalloprotein, bearing minimal net negative charge (e.g., Z=-2.0) binds one or more metal cations, is the net charge abolished or inverted to positive? Or do metalloproteins regulate net charge when coordinating metal ions? The author's group has recently dusted off a relatively obscure tool-the "protein charge ladder"-and used it to begin to answer these basic questions.

Experimental Mutations in Superoxide Dismutase 1 Provide Insight into Potential Mechanisms Involved in Aberrant Aggregation in Familial Amyotrophic Lateral Sclerosis

Mutations in more than 80 different positions in superoxide dismutase 1 (SOD1) have been associated with amyotrophic lateral sclerosis (fALS). There is substantial evidence that a common consequence of these mutations is to induce the protein to misfold and aggregate. How these mutations perturb native structure to heighten the propensity to misfold and aggregate is unclear. In the present study, we have mutagenized Glu residues at positions 40 and 133 that are involved in stabilizing the β-barrel structure of the native protein and a critical Zn binding domain, respectively, to examine how specific mutations may cause SOD1 misfolding and aggregation. Mutations associated with ALS as well as experimental mutations were introduced into these positions. We used an assay in which mutant SOD1 was fused to yellow fluorescent protein (SOD1:YFP) to visualize the formation of cytosolic inclusions by mutant SOD1. We then used existing structural data on SOD1, to predict how different mutations might alter local 3D conformation. Our findings reveal an association between mutant SOD1 aggregation and amino acid substitutions that are predicted to introduce steric strain, sometimes subtly, in the 3D conformation of the peptide backbone.

Molecular Mechanisms of TDP-43 Misfolding and Pathology in Amyotrophic Lateral Sclerosis

TAR DNA binding protein 43 (TDP-43) is a versatile RNA/DNA binding protein involved in RNA-related metabolism. Hyper-phosphorylated and ubiquitinated TDP-43 deposits act as inclusion bodies in the brain and spinal cord of patients with the motor neuron diseases: amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). While the majority of ALS cases (90-95%) are sporadic (sALS), among familial ALS cases 5-10% involve the inheritance of mutations in the TARDBP gene and the remaining (90-95%) are due to mutations in other genes such as: C9ORF72, SOD1, FUS, and NEK1 etc. Strikingly however, the majority of sporadic ALS patients (up to 97%) also contain the TDP-43 protein deposited in the neuronal inclusions, which suggests of its pivotal role in the ALS pathology. Thus, unraveling the molecular mechanisms of the TDP-43 pathology seems central to the ALS therapeutics, hence, we comprehensively review the current understanding of the TDP-43's pathology in ALS. We discuss the roles of TDP-43's mutations, its cytoplasmic mis-localization and aberrant post-translational modifications in ALS. Also, we evaluate TDP-43's amyloid-like in vitro aggregation, its physiological vs. pathological oligomerization in vivo, liquid-liquid phase separation (LLPS), and potential prion-like propagation propensity of the TDP-43 inclusions. Finally, we describe the various evolving TDP-43-induced toxicity mechanisms, such as the impairment of endocytosis and mitotoxicity etc. and also discuss the emerging strategies toward TDP-43 disaggregation and ALS therapeutics.

Glycerolipid Headgroups Control Rate and Mechanism of Superoxide Dismutase-1 Aggregation and Accelerate Fibrillization of Slowly Aggregating Amyotrophic Lateral Sclerosis Mutants

Interactions between superoxide dismutase-1 (SOD1) and lipid membranes might be directly involved in the toxicity and intercellular propagation of aggregated SOD1 in amyotrophic lateral sclerosis (ALS), but the chemical details of lipid-SOD1 interactions and their effects on SOD1 aggregation remain unclear. This paper determined the rate and mechanism of nucleation of fibrillar apo-SOD1 catalyzed by liposomal surfaces with identical hydrophobic chains (RCH₂(O₂C₁₈H₃₃)₂), but headgroups of different net charge and hydrophobicity (i.e., R(CH₂)N⁺(CH₃)₃, RPO₄^-(CH₂)₂N⁺(CH₃)₃, and RPO₄^-). Under semiquiescent conditions (within a 96 well microplate, without a gyrating bead), the aggregation of apo-SOD1 into thioflavin-T-positive (ThT(+)) amyloid fibrils did not occur over 120 h in the absence of liposomal surfaces. Anionic liposomes triggered aggregation of apo-SOD1 into ThT(+) amyloid fibrils; cationic liposomes catalyzed fibrillization but at slower rates and across a narrower lipid concentration; zwitterionic liposomes produced nonfibrillar (amorphous) aggregates. The inability of zwitterionic liposomes to catalyze fibrillization and the dependence of fibrillization rate on anionic lipid concentration suggests that membranes catalyze SOD1 fibrillization by a primary nucleation mechanism. Membrane-catalyzed fibrillization was also examined for eight ALS variants of apo-SOD1, including G37R, G93R, D90A, and E100G apo-SOD1 that nucleate slower than or equal to WT SOD1 in lipid-free, nonquiescent amyloid assays. All ALS variants (with one exception) nucleated faster than WT SOD1 in the presence of anionic liposomes, wherein the greatest acceleratory effects were observed among variants with lower net negative surface charge (G37R, G93R, D90A, E100G). The exception was H46R apo-SOD1, which did not form ThT(+) species.

The amyloidogenicity of a C-terminal region of TDP-43 implicated in Amyotrophic Lateral Sclerosis can be affected by anions, acetylation and homodimerization

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease associated with accumulation of hyper-phosphorylated, and ubiquitinated TAR DNA-binding protein-43 (TDP-43) as inclusion deposits in neuronal cells. Recently, amyloid-like fibrillar aggregates of TDP-43 have been reported from several ALS patients. The C-terminal region of TDP-43 is central to TDP-43's pathological aggregation and most of the familial ALS mutations in the encoding TARDBP gene are located in this domain. Also, aberrant proteolytic cleavages of TDP-43 produce cytotoxic C-terminal fragments of ∼15-35 kDa. The C-terminal end harbours a glycine-rich region and a Q/N rich prion-like aggregation-prone domain which has been shown to form amyloid-like fibrillar aggregates in vitro. Previously, TDP-43 protein has also been shown to undergo several other post-translational modifications such as acetylation and dimerization, however, their effects on TDP-43's amyloid-like in vitro aggregation have not been examined. Towards this, we have here examined effects of anions, acetylation and homodimerization on the in vitro aggregation of a C-terminal fragment (amino acid: 193-414) of TDP-43 termed TDP-43^2C. We find that kosmotropic anions greatly accelerate whereas chaotropic anions impede its aggregation. Also, we show that acetylation of certain lysines in C-terminal fragments significantly reduces the TDP-43^2C's amyloid-like aggregation. Furthermore, we separated spontaneously formed cysteine-linked homodimers of the recombinantly purified TDP-43^2C using size-exclusion chromatography and found that these dimers retain amyloidogenicity. These findings would be of significance to the TDP-43 aggregation-induced pathology in ALS.

Paclitaxel inhibited lysozyme fibrillation by increasing colloidal stability through formation of "off-pathway" oligomers

Protein fibrillation is a challenging issue in medicine, causing many diseases, and an impediment to pharmaceutics and protein industry. Many chemicals, especially polyphenol compounds and aromatic small molecules, have been widely used as an effective strategy to combat protein fibril formation. Hence, understanding mechanisms of fibrillation inhibition and contributing forces in this process are significant. In this study, the inhibitory effect of paclitaxel on lysozyme fibrillation was investigated with respect to thermal and colloidal stability. Fibrillation was monitored with ThT fluorescence, circular dichroism, and AFM; paclitaxel-lysozyme interaction with isothermal titration calorimetry and docking; thermal and colloidal stability with differential scanning calorimetry and zeta-pulse, respectively. Paclitaxel inhibited lysozyme fibrillation, and interacted with lysozyme through hydrogen bonds and van der Waals' interactions. The viability of PC12 cells retrieved as a result of fibrillation inhibition by paclitaxel. Hydrophobic forces dominantly shielded the aggregation-prone region of lysozyme and suppressed the effective interactions between lysozyme monomers. Although paclitaxel did not affect lysozyme's thermal stability, it increased lysozyme's colloidal stability by either increasing the surface charge density or charge distribution on lysozyme. In conclusion, our results suggest a model for paclitaxel's inhibitory role through two complementary steps driving to "off-pathway" oligomer formation and attenuation of fibril formation.

Aspirin-Mediated Acetylation Protects Against Multiple Neurodegenerative Pathologies by Impeding Protein Aggregation

AIMS

Many progressive neurological disorders, including Alzheimer's disease (AD), Huntington's disease, and Parkinson's disease (PD), are characterized by accumulation of insoluble protein aggregates. In prospective trials, the cyclooxygenase inhibitor aspirin (acetylsalicylic acid) reduced the risk of AD and PD, as well as cardiovascular events and many late-onset cancers. Considering the role played by protein hyperphosphorylation in aggregation and neurodegenerative diseases, and aspirin's known ability to donate acetyl groups, we asked whether aspirin might reduce both phosphorylation and aggregation by acetylating protein targets.

RESULTS

Aspirin was substantially more effective than salicylate in reducing or delaying aggregation in human neuroblastoma cells grown in vitro, and in Caenorhabditis elegans models of human neurodegenerative diseases in vivo. Aspirin acetylates many proteins, while reducing phosphorylation, suggesting that acetylation may oppose phosphorylation. Surprisingly, acetylated proteins were largely excluded from compact aggregates. Molecular-dynamic simulations indicate that acetylation of amyloid peptide energetically disfavors its association into dimers and octamers, and oligomers that do form are less compact and stable than those comprising unacetylated peptides.

INNOVATION

Hyperphosphorylation predisposes certain proteins to aggregate (e.g., tau, α-synuclein, and transactive response DNA-binding protein 43 [TDP-43]), and it is a critical pathogenic marker in both cardiovascular and neurodegenerative diseases. We present novel evidence that acetylated proteins are underrepresented in protein aggregates, and that aggregation varies inversely with acetylation propensity after diverse genetic and pharmacologic interventions.

CONCLUSIONS

These results are consistent with the hypothesis that aspirin inhibits protein aggregation and the ensuing toxicity of aggregates through its acetyl-donating activity. This mechanism may contribute to the neuro-protective, cardio-protective, and life-prolonging effects of aspirin. Antioxid. Redox Signal. 27, 1383-1396.

Mellitate: A multivalent anion with extreme charge density causes rapid aggregation and misfolding of wild type lysozyme at neutral pH

Due to its symmetric structure and abundance of carboxyl groups, mellitic acid (MA–benzenehexacarboxylic acid) has an uncommon capacity to form highly ordered molecular networks. Dissolved in water, MA dissociates to yield various mellitate anions with pronounced tendencies to form complexes with cations including protonated amines. Deprotonation of MA at physiological pH produces anions with high charge densities (MA^5- and MA^6-) whose influence on co-dissolved proteins has not been thoroughly studied. As electrostatic attraction between highly symmetric MA^6- anions and positively charged low-symmetry globular proteins could lead to interesting self-assembly patterns we have chosen hen egg white lysozyme (HEWL), a basic stably folded globular protein as a cationic partner for mellitate anions to form such hypothetical nanostructures. Indeed, mixing of neutral HEWL and MA solutions does result in precipitation of electrostatic complexes with the stoichiometry dependent on pH. We have studied the self-assembly of HEWL-MA structures using vibrational spectroscopy (infrared absorption and Raman scattering), circular dichroism (CD), atomic force microscopy (AFM). Possible HEWL-MA^6- molecular docking scenarios were analyzed using computational tools. Our results indicate that even at equimolar ratios (in respect to HEWL), MA^5- and MA^6- anions are capable of inducing misfolding and aggregation of the protein upon mild heating which results in non-native intermolecular beta-sheet appearing in the amide I’ region of the corresponding infrared spectra. The association process leads to aggregates with compacted morphologies entrapping mellitate anions. The capacity of extremely diluted mellitate anions (i.e. at sub-millimolar concentration range) to trigger aggregation of proteins is discussed in the context of mechanisms of misfolding.

Lysine acylation in superoxide dismutase-1 electrostatically inhibits formation of fibrils with prion-like seeding

The acylation of lysine residues in superoxide dismutase-1 (SOD1) has been previously shown to decrease its rate of nucleation and elongation into amyloid-like fibrils linked to amyotrophic lateral sclerosis. The chemical mechanism underlying this effect is unclear, i.e. hydrophobic/steric effects versus electrostatic effects. Moreover, the degree to which the acylation might alter the prion-like seeding of SOD1 in vivo has not been addressed. Here, we acylated a fraction of lysine residues in SOD1 with groups of variable hydrophobicity, charge, and conformational entropy. The effect of each acyl group on the rate of SOD1 fibril nucleation and elongation were quantified in vitro with thioflavin-T (ThT) fluorescence, and we performed 594 iterate aggregation assays to obtain statistically significant rates. The effect of the lysine acylation on the prion-like seeding of SOD1 was assayed in spinal cord extracts of transgenic mice expressing a G85R SOD1-yellow fluorescent protein construct. Acyl groups with >2 carboxylic acids diminished self-assembly into ThT-positive fibrils and instead promoted the self-assembly of ThT-negative fibrils and amorphous complexes. The addition of ThT-negative, acylated SOD1 fibrils to organotypic spinal cord failed to produce the SOD1 inclusion pathology that typically results from the addition of ThT-positive SOD1 fibrils. These results suggest that chemically increasing the net negative surface charge of SOD1 via acylation can block the prion-like propagation of oligomeric SOD1 in spinal cord.

Acylation of Superoxide Dismutase 1 (SOD1) at K122 Governs SOD1-Mediated Inhibition of Mitochondrial Respiration

In this study, we employed proteomics to identify mechanisms of posttranslational regulation on cell survival signaling proteins. We focused on Cu-Zn superoxide dismutase (SOD1), which protects cells from oxidative stress. We found that acylation of K122 on SOD1, while not impacting SOD1 catalytic activity, suppressed the ability of SOD1 to inhibit mitochondrial metabolism at respiratory complex I. We found that deacylase depletion increased K122 acylation on SOD1, which blocked the suppression of respiration in a K122-dependent manner. In addition, we found that acyl-mimicking mutations at K122 decreased SOD1 accumulation in mitochondria, initially hinting that SOD1 may inhibit respiration directly within the intermembrane space (IMS). However, surprisingly, we found that forcing the K122 acyl mutants into the mitochondria with an IMS-targeting tag did not recover their ability to suppress respiration. Moreover, we found that suppressing or boosting respiration levels toggled SOD1 in or out of the mitochondria, respectively. These findings place SOD1-mediated inhibition of respiration upstream of its mitochondrial localization. Lastly, deletion-rescue experiments show that a respiration-defective mutant of SOD1 is also impaired in its ability to rescue cells from toxicity caused by SOD1 deletion. Together, these data suggest a previously unknown interplay between SOD1 acylation, metabolic regulation, and SOD1-mediated cell survival.

Kaplan-Meier Meets Chemical Kinetics: Intrinsic Rate of SOD1 Amyloidogenesis Decreased by Subset of ALS Mutations and Cannot Fully Explain Age of Disease Onset

Over 150 mutations in SOD1 (superoxide dismutase-1) cause amyotrophic lateral sclerosis (ALS), presumably by accelerating SOD1 amyloidogenesis. Like many nucleation processes, SOD1 fibrillization is stochastic (in vitro), which inhibits the determination of aggregation rates (and obscures whether rates correlate with patient phenotypes). Here, we diverged from classical chemical kinetics and used Kaplan-Meier estimators to quantify the probability of apo-SOD1 fibrillization (in vitro) from ∼10³ replicate amyloid assays of wild-type (WT) SOD1 and nine ALS variants. The probability of apo-SOD1 fibrillization (expressed as a Hazard ratio) is increased by certain ALS-linked SOD1 mutations but is decreased or remains unchanged by other mutations. Despite this diversity, Hazard ratios of fibrillization correlated linearly with (and for three mutants, approximately equaled) Hazard ratios of patient survival (R² = 0.67; Pearson's r = 0.82). No correlation exists between Hazard ratios of fibrillization and age of initial onset of ALS (R² = 0.09). Thus, Hazard ratios of fibrillization might explain rates of disease progression but not onset. Classical kinetic metrics of fibrillization, i.e., mean lag time and propagation rate, did not correlate as strongly with phenotype (and ALS mutations did not uniformly accelerate mean rate of nucleation or propagation). A strong correlation was found, however, between mean ThT fluorescence at lag time and patient survival (R² = 0.93); oligomers of SOD1 with weaker fluorescence correlated with shorter survival. This study suggests that SOD1 mutations trigger ALS by altering a property of SOD1 or its oligomers other than the intrinsic rate of amyloid nucleation (e.g., oligomer stability; rates of intercellular propagation; affinity for membrane surfaces; and maturation rate).

Peptide Conjugates of Benzene Carboxylic Acids as Agonists and Antagonists of Amylin Aggregation

Human islet amyloid polypeptide (hIAPP), also known as amylin, is a 37 residue peptide hormone that is stored and co-secreted with insulin. hIAPP plays a pivotal role in type 2 diabetes and is the major component of amyloid deposits found in the pancreas of patients afflicted with the disease. The self-assembly of hIAPP and the formation of amyloid is linked to the death of insulin producing β-cells. Recent findings suggest that soluble hIAPP oligomers are the cytotoxic species responsible for β-cell loss whereas amyloid fibrils themselves may indeed be innocuous. Potential avenues of therapeutic intervention include the development of compounds that prevent hIAPP self-assembly as well as those that reduce or eliminate lag time and rapidly accelerate the formation of amyloid fibrils. Both of these approaches minimize temporal exposure to soluble cytotoxic hIAPP oligomers. Toward this end our laboratory has pursued an electrostatic repulsion approach to the development of potential inhibitors and modulators of hIAPP self-assembly. Peptide conjugates were constructed in which benzene carboxylic acids of varying charge were employed as electrostatic disrupting elements and appended to the N-terminal of the hIAPP_22-29 (NFGAILSS) self-recognition sequence. The self-assembly kinetics of conjugates were characterized by turbidity measurements and the structure of aggregates probed by Raman and CD spectroscopy while the morphology was assessed using transmission electron microscopy. Several benzene carboxylic acid peptide conjugates failed to self-assemble and some were found to inhibit the aggregation of full-length amylin while others served to enhance the rate of amyloid formation and/or increase the yield of amyloid produced. Studies reveal that the geometric display of free carboxylates on the benzene ring of the conjugates plays an important role in the activity of conjugates. In addition, a number of free benzene carboxylic acids were found to modulate amylin self-assembly on their own. The results of these investigations confirm the viability of the electrostatic repulsion approach to the modulation of amyloid formation and may aid the design and development of potential therapeutic agents.

How Do Gyrating Beads Accelerate Amyloid Fibrillization?

The chemical and physical mechanisms by which gyrating beads accelerate amyloid fibrillization in microtiter plate assays are unclear. Identifying these mechanisms will help optimize high-throughput screening assays for molecules and mutations that modulate aggregation and might explain why different research groups report different rates of aggregation for identical proteins. This article investigates how the rate of superoxide dismutase-1 (SOD1) fibrillization is affected by 12 different beads with a wide range of hydrophobicity, mass, stiffness, and topology but identical diameter. All assays were performed on D90A apo-SOD1, which is a stable and wild-type-like variant of SOD1. The most significant and uniform correlation between any material property of each bead and that bead's effect on SOD1 fibrillization rate was with regard to bead mass. A linear correlation existed between bead mass and rate of fibril elongation (R2 = 0.7): heavier beads produced faster rates and shorter fibrils. Nucleation rates (lag time) also correlated with bead mass, but only for non-polymeric beads (i.e., glass, ceramic, metallic). The effect of bead mass on fibrillization correlated (R2 = 0.96) with variations in buoyant forces and contact forces (between bead and microplate well), and was not an artifact of residual momentum during intermittent gyration. Hydrophobic effects were observed, but only for polymeric beads: lag times correlated negatively with contact angle of water and degree of protein adhesion (surface adhesion and hydrophobic effects were negligible for non-polymeric beads). These results demonstrate that contact forces (alone) explain kinetic variation among non-polymeric beads, whereas surface hydrophobicity and contact forces explain kinetic variation among polymeric beads. This study also establishes conditions for high-throughput amyloid assays of SOD1 that enable the control over fibril morphologies and produce eightfold faster lag times and fourfold less stochasticity than in previous studies.

Effect of a small dose of aspirin on quantitative test of 24-h urinary protein in patients with hypertension in pregnancy

The aim of the present study was to determine the effect of a small dose of aspirin on a quantitative test of 24-h urinary protein in patients with hypertension in pregnancy. In total, 224 patients with hypertension in pregnancy were continuously selected and were randomly divided into the control group (50 cases with conventional therapy), aspirin 50 mg/day group (60 cases), aspirin 75 mg/day group (58 cases), and aspirin 100 mg/day group (56 cases). Clinical effects were compared from 16 gestational weeks to childbirth. According to the comparison in the four groups, there was no statistical difference in the mean arterial pressure, pre-eclampsia rate, gestational weeks, and caesarean section rate (p>0.05). The 24-h urinary protein and endothelin-1 (ET-1) level were significantly decreased following treatment, and were less than the control and 50 mg/day groups. The superoxide dismutase (SOD) level was significantly increased, and higher than the control and 50 mg/day groups. In terms of the 75 and 100 mg/day, control and 50 mg/day groups, there was no statistical difference (p>0.05). A comparison of the complication rate in the four groups of fetuses during the perinatal period, no statistical difference was observed (p>0.05). Thus, the results show that, regarding patients with hypertension in pregnancy, 75 mg/day aspirin can decrease the 24-h urinary protein, SOD, and ET-1 level. However, the results remain to be confirmed to improve maternal and infant outcome in delivery.

From the Evolution of Protein Sequences Able to Resist Self-Assembly to the Prediction of Aggregation Propensity

Folding of polypeptide chains into biologically active entities is an astonishingly complex process, determined by the nature and the sequence of residues emerging from ribosomes. While it has been long believed that evolution has pressed genomes so that specific sequences could adopt unique, functional three-dimensional folds, it is now clear that complex protein machineries act as quality control system and supervise folding. Notwithstanding that, events such as erroneous folding, partial folding, or misfolding are frequent during the life of a cell or a whole organism, and they can escape controls. One of the possible outcomes of this misbehavior is cross-β aggregation, a super secondary structure which represents the hallmark of self-assembled, well organized, and extremely ordered structures termed amyloid fibrils. What if evolution would have not taken into account such possibilities? Twenty years of research point toward the idea that, in fact, evolution has constantly supervised the risk of errors and minimized their impact. In this review we tried to survey the major findings in the amyloid field, trying to describe what the real pitfalls of protein folding are-from an evolutionary perspective-and how sequence and structural features have evolved to balance the need for perfect, dynamic, functionally efficient structures, and the detrimental effects implicit in the dangerous process of folding. We will discuss how the knowledge obtained from these studies has been employed to produce computational methods able to assess, predict, and discriminate the aggregation properties of protein sequences.

Stochastic Formation of Fibrillar and Amorphous Superoxide Dismutase Oligomers Linked to Amyotrophic Lateral Sclerosis

Recent reports suggest that the nucleation and propagation of oligomeric superoxide dismutase-1 (SOD1) is effectively stochastic in vivo and in vitro. This perplexing kinetic variability-observed for other proteins and frequently attributed to experimental error-plagues attempts to discern how SOD1 mutations and post-translational modifications linked to amyotrophic lateral sclerosis (ALS) affect SOD1 aggregation. This study used microplate fluorescence spectroscopy and dynamic light scattering to measure rates of fibrillar and amorphous SOD1 aggregation at high iteration (ntotal = 1.2 × 10(3)). Rates of oligomerization were intrinsically irreproducible and populated continuous probability distributions. Modifying reaction conditions to mimic random and systematic experimental error could not account for kinetic outliers in standard assays, suggesting that stochasticity is not an experimental artifact, rather an intrinsic property of SOD1 oligomerization (presumably caused by competing pathways of oligomerization). Moreover, mean rates of fibrillar and amorphous nucleation were not uniformly increased by mutations that cause ALS; however, mutations did increase kinetic noise (variation) associated with nucleation and propagation. The stochastic aggregation of SOD1 provides a plausible statistical framework to rationalize how a pathogenic mutation can increase the probability of oligomer nucleation within a single cell, without increasing the mean rate of nucleation across an entire population of cells.

Electrostatically-guided inhibition of Curli amyloid nucleation by the CsgC-like family of chaperones

Polypeptide aggregation into amyloid is linked with several debilitating human diseases. Despite the inherent risk of aggregation-induced cytotoxicity, bacteria control the export of amyloid-prone subunits and assemble adhesive amyloid fibres during biofilm formation. An Escherichia protein, CsgC potently inhibits amyloid formation of curli amyloid proteins. Here we unlock its mechanism of action, and show that CsgC strongly inhibits primary nucleation via electrostatically-guided molecular encounters, which expands the conformational distribution of disordered curli subunits. This delays the formation of higher order intermediates and maintains amyloidogenic subunits in a secretion-competent form. New structural insight also reveal that CsgC is part of diverse family of bacterial amyloid inhibitors. Curli assembly is therefore not only arrested in the periplasm, but the preservation of conformational flexibility also enables efficient secretion to the cell surface. Understanding how bacteria safely handle amyloidogenic polypeptides contribute towards efforts to control aggregation in disease-causing amyloids and amyloid-based biotechnological applications.

Voltage-Induced Misfolding of Zinc-Replete ALS Mutant Superoxide Dismutase-1

The monomerization of Cu, Zn superoxide dismutase (SOD1) is an early step along pathways of misfolding linked to amyotrophic lateral sclerosis (ALS). Monomerization requires the reversal of two post-translational modifications that are thermodynamically favorable: (i) dissociation of active-site metal ions and (ii) reduction of intramolecular disulfide bonds. This study found, using amide hydrogen/deuterium (H/D) exchange, capillary electrophoresis, and lysine-acetyl protein charge ladders, that ALS-linked A4V SOD1 rapidly monomerizes and partially unfolds in an external electric field (of physiological strength), without loss of metal ions, exposure to disulfide-reducing agents, or Joule heating. Voltage-induced monomerization was not observed for metal-free A4V SOD1, metal-free WT SOD1, or metal-loaded WT SOD1. Computational modeling suggested a mechanism for this counterintuitive effect: subunit macrodipoles of dimeric SOD1 are antiparallel and amplified 2-fold by metal coordination, which increases torque at the dimer interface as subunits rotate to align with the electric field.