Conformational dynamics of superoxide dismutase (SOD1) in osmolytes: a molecular dynamics simulation study

Copper toxicity and deficiency: the vicious cycle at the core of protein aggregation in ALS

The pathophysiology of ALS involves many signs of a disruption in copper homeostasis, with both excess free levels and functional deficiency likely occurring simultaneously. This is crucial, as many important physiological functions are performed by cuproenzymes. While it is unsurprising that many ALS symptoms are related to signs of copper deficiency, resulting in vascular, antioxidant system and mitochondrial oxidative respiration deficiencies, there are also signs of copper toxicity such as ROS generation and enhanced protein aggregation. We discuss how copper also plays a key role in proteostasis and interacts either directly or indirectly with many of the key aggregate-prone proteins implicated in ALS, such as TDP-43, C9ORF72, SOD1 and FUS as well as the effect of their aggregation on copper homeostasis. We suggest that loss of cuproprotein function is at the core of ALS pathology, a condition that is driven by a combination of unbound copper and ROS that can either initiate and/or accelerate protein aggregation. This could trigger a positive feedback cycle whereby protein aggregates trigger the aggregation of other proteins in a chain reaction that eventually captures elements of the proteostatic mechanisms in place to counteract them. The end result is an abundance of aggregated non-functional cuproproteins and chaperones alongside depleted intracellular copper stores, resulting in a general lack of cuproenzyme function. We then discuss the possible aetiology of ALS and illustrate how strong risk factors including environmental toxins such as BMAA and heavy metals can functionally behave to promote protein aggregation and disturb copper metabolism that likely drives this vicious cycle in sporadic ALS. From this synthesis, we propose restoration of copper balance using copper delivery agents in combination with chaperones/chaperone mimetics, perhaps in conjunction with the neuroprotective amino acid serine, as a promising strategy in the treatment of this incurable disease.

Inhibitors against New Delhi metallo-betalactamase-1 (NDM-1) and its variants endemic in Indian settings along with the laboratory functional gain mutant of NDM-1

PURPOSE

The emergence of NDM-1 producing bacteria has become common in both hospital and community settings, but no inhibitor has yet been available for clinical treatment. Hence, demanding the urgent need of NDM-1 inhibitors, we initiated to screen broad spectrum inhibitors against NDM natural variants and laboratory mutant.

METHODS

We used docking and molecular dynamics simulations, in silico pharmacokinetic investigations, and density functional theory calculation to characterize molecules. Furthermore, an in vitro study, including MIC, kinetics, and fluorescence study were carried out to confirm the efficacies of the selected compounds.

RESULTS

According to the findings of the computational studies, three compounds were effective against NDM variants. Fourfold reduction in MIC of imipenem and meropenem was observed when combined with inhibitors (D2573, D2148, and D63) against blaNDM-1, blaNDM-4, blaNDM-6, and blaNDM-1Q123A, while twofold reduction in MIC of imipenem and meropenem was observed against blaNDM-5 and blaNDM-7. Similarly in the presence of inhibitors (D2573, D2148, and D63) the efficiency of nitrocefin hydrolysis by NDM-4, NDM-6, and Q123A decreases to much more extent as compared to NDM-5 and NDM-7. These results showed that the efficacy of these broad spectrum inhibitors decreases with increasing resistance of NDM variants.

CONCLUSION

This is the first time inhibitors were tested against different NDM natural variants which are endemic in Indian settings. Moreover, a functional gain laboratory mutant was also checked for their efficacies. We may propose these molecules for the pre-clinical trial to further translate.

Implications of ALS-Associated Mutations on Biochemical and Biophysical Features of hSOD1 and Aggregation Formation

One of the recognized motor neuron degenerative disorders is amyotrophic lateral sclerosis (ALS). By now, several mutations have been reported and linked to ALS patients, some of which are induced by mutations in the human superoxide dismutase (hSOD1) gene. The ALS-provoking mutations are located throughout the structure of hSOD1 and promote the propensity to aggregate. Despite numerous investigations, the underlying mechanism related to the toxicity of mutant hSOD1 through the gain of a toxic function is still vague. We surveyed two mutant forms of hSOD1 by removing and adding cysteine at positions 146 and 72, respectively, to investigate the biochemical characterization and amyloid formation. Our findings predicted the harmful and destabilizing impact of two SOD1 mutants using multiple programs. The specific activity of the wild-type form was about 1.42- and 1.92-fold higher than that of C146R and G72C mutants, respectively. Comparative structural studies using CD spectropolarimetry, and intrinsic and ANS fluorescence showed alterations in secondary structure content, exposure of hydrophobic patches, and structural compactness of WT-hSOD1 vs. mutants. We demonstrated that two mutants were able to promote amyloid-like aggregates under amyloid induction circumstances (50-mM Tris-HCl pH 7.4, 0.2-M KSCN, 50-mM DTT, 37 °C, 190 rpm). Monitoring aggregates were done using an enhancement in thioflavin T fluorescence and alterations in Congo red absorption. The mutants accelerated fibrillation with subsequently greater fluorescence amplitude and a shorter lag time compared to WT-SOD1. These findings support the aggregation of ALS-associated SOD1 mutants as an integral part of ALS pathology.

Unveiling local and global conformational changes and allosteric communications in SOD1 systems using molecular dynamics simulation and network analyses

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a serious neurodegenerative disorder affecting nerve cells in the brain and spinal cord that is caused by mutations in the superoxide dismutase 1 (SOD1) enzyme. ALS-related mutations cause misfolding, dimerisation instability, and increased formation of aggregates. The underlying allosteric mechanisms, however, remain obscure as far as details of their fundamental atomistic structure are concerned. Hence, this gap in knowledge limits the development of novel SOD1 inhibitors and the understanding of how disease-associated mutations in distal sites affect enzyme activity.

METHODS

We combined microsecond-scale based unbiased molecular dynamics (MD) simulation with network analysis to elucidate the local and global conformational changes and allosteric communications in SOD1 Apo (unmetallated form), Holo, Apo_CallA (mutant and unmetallated form), and Holo_CallA (mutant form) systems. To identify hotspot residues involved in SOD1 signalling and allosteric communications, we performed network centrality, community network, and path analyses.

RESULTS

Structural analyses showed that unmetallated SOD1 systems and cysteine mutations displayed large structural variations in the catalytic sites, affecting structural stability. Inter- and intra H-bond analyses identified several important residues crucial for maintaining interfacial stability, structural stability, and enzyme catalysis. Dynamic motion analysis demonstrated more balanced atomic displacement and highly correlated motions in the Holo system. The rationale for structural disparity observed in the disulfide bond formation and R143 configuration in Apo and Holo systems were elucidated using distance and dihedral probability distribution analyses.

CONCLUSION

Our study highlights the efficiency of combining extensive MD simulations with network analyses to unravel the features of protein allostery.

Rational design and synthesis of novel triazole- and tetrazole-fused iminosugars as potential inhibitors of amyotrophic lateral sclerosis (ALS) linked SOD1 aggregation

In this manuscript we report the first example of an iminosugar that inhibits superoxide dismutase fibrillation associated with the amyotrophic lateral sclerosis (ALS). The present work involves synthesis of novel triazole and tetrazole embedded iminosugars, synthesized in 11-13 high yielding steps starting from readily available tri-O-benzyl-D-glucal and proceeding through a concomitant azidation - thermal intramolecular [3 + 2] cycloaddition reaction as the key step. One of these pre-designed iminosugars was found to inhibit fibrillation of SOD1 and also has shown propensity to break pre-formed fibrils. Docking and MD simulation studies suggest that the most probable interaction of this compound is a hydrogen bonding with Arg69, a loop IV residue of SOD1, which has a crucial role in stabilizing the native conformation of SOD1.

Repurposing FDA approved drug molecules against A B C classes of β-lactamases: a computational biology and molecular dynamics simulations study

β-lactamase are the main resistance factor for β-lactam antibiotics in Gram-negative bacteria. Since β-lactam antibiotics are being utilised as an antimicrobial agents extensively for the past 70 years, a large number of β-lactam-inactivating β-lactamases have been produced by bacteria. Here, we employed a structure-based drug discovery approach to identify and assess the efficacy of a potential medication that might block the β-lactamases which hydrolyse antibiotics. The FDA-approved medications were subjected to virtual screening, molecular docking, molecular dynamics simulations, density functional theory, and covalent docking against the β-lactamases. We identified diosmin, hidrosmin, monoxuritin and solasulfone as β-lactamase inhibitors which are authorised for therapeutic use in humans. These medications interact in a remarkable variety of non-covalent ways with the conserved residues in the substrate-binding pocket of the β-lactamases. Diosmin has been identified as an inhibitor that binds covalently to the NDM-1 a class B metallo-betalactamase. After experimental validation and clinical demonstration, this study offers adequate evidence for the therapeutic use of these drugs for controlling multidrug resistance.Communicated by Ramaswamy H. Sarma.

Computational modelling of potential Zn-sensitive non-β-lactam inhibitors of imipenemase-1 (IMP-1)

Antibiotic resistance (AR) remains one of the leading global health challenges, mostly implicated in disease-related deaths. The Enterobacteriaceae-producing metallo-β-lactamases (MBLs) are critically involved in AR pathogenesis through Zn-dependent catalytic destruction of β-lactam antibiotics, yet with limited successful clinical inhibitors. The efficacy of relevant broad-spectrum β-lactams including imipenem and meropenem are seriously challenged by their susceptibility to the Zn-dependent carbapenemase hydrolysis, as such, searching for alternatives remains imperative. In this study, computational molecular modelling and virtual screening methods were extensively applied to identify new putative Zn-sensitive broad-spectrum inhibitors of MBLs, specifically imipenemase-1 (IMP-1) from the IBScreen database. Three ligands, STOCK3S-30154, STOCK3S-30418 and STOCK3S-30514 selectively displayed stronger binding interactions with the enzymes compared to reference inhibitors, imipenem and meropenem. For instance, the ligands showed molecular docking scores of -9.450, -8.005 and -10.159 kcal/mol, and MM-GBSA values of -40.404, -31.902 and -33.680 kcal/mol respectively against the IMP-1. Whereas, imipenem and meropenem showed docking scores of -9.038 and -10.875 kcal/mol, and MM-GBSA of -31.184 and -32.330 kcal/mol respectively against the enzyme. The ligands demonstrated good thermodynamic stability and compactness in complexes with IMP-1 throughout the 100 ns molecular dynamics (MD) trajectories. Interestingly, their binding affinities and stabilities were significantly affected in contacts with the remodelled Zn-deficient IMP-1, indicating sensitivity to the carbapenemase active Zn site, however, with non-β-lactam scaffolds, tenable to resist catalytic hydrolysis. They displayed ideal drug-like ADMET properties, thus, representing putative Zn-sensitive non-β-lactam inhibitors of IMP-1 amenable for further experimental studies.

Elucidation of kinetic and structural properties of eye lens ζ-crystallin: an in vitro and in silico approach

The Arabian Camelus dromedarius contains significant concentration of eye lens ζ-crystallin. This enzyme is also present in other life forms including humans, however in lower catalytic amounts. The recombinant camel ζ-crystallin was expressed in the E. coli BL21 (DE3) pLysS strain and purified using HisTrap column. The K_m of the enzyme for 9,10-phenanthrenequinone (9,10-PQ) substrate and NADPH cofactor was determined to be 11.66 and 50.93 µM, respectively. The V_max for 9,10-PQ and NADPH was obtained as 23.19 and 19.98 μM min^-1, respectively. The optimum activity of the purified enzyme was found to be at pH 6.0 and at 55 °C. Different physico-chemical parameters were analysed including instability index (II), aliphatic index (AI) and the GRAVY index to establish proper characterization. The sequence of the recombinant ζ-crystallin was subjected to homology modelling using SWISS-MODEL webserver followed by validation of the modelled target structure. The evaluation of the modelled ζ-crystallin was performed by several parameters including Ramachandran plot, Z-score values followed by molecular dynamics (MD) simulation. The cumulative analysis of the physico-chemical, quantitative, qualitative and the essential dynamics of simulation of ζ-crystallin and its complexes with 9,10-PQ and NADPH helped in verifying the acceptable quality and stability of the ζ-crystallin structure.Communicated by Ramaswamy H. Sarma.

Computational insight into in silico analysis and molecular dynamics simulation of the dimer interface residues of ALS-linked hSOD1 forms in apo/holo states: a combined experimental and bioinformatic perspective

The aggregation of misfolded SOD1 proteins in neurodegenerative illnesses is a key pathological hallmark in amyotrophic lateral sclerosis (ALS). SOD1 is stabilized and enzymatically activated after binding to Cu/Zn and forming intramolecular disulfide. SOD1 aggregation/oligomerization is triggered by the dissociation of Cu and/or Zn ions. Therefore, we compared the possible effects of ALS-associated point mutations of the holo/apo forms of WT/I149T/V148G SOD1 variants located at the dimer interface to determine structural characterization using spectroscopic methods, computational approaches as well as molecular dynamics (MD) simulations. Predictive results of computational analysis of single-nucleotide polymorphisms (SNPs) suggested that mutant SOD1 has a deleterious effect on activity and structure destabilization. MD data analysis indicated that changes in flexibility, stability, hydrophobicity of the protein as well as increased intramolecular interactions of apo-SOD1 were more than holo-SOD1. Furthermore, a decrease in enzymatic activity in apo-SOD1 was observed compared to holo-SOD1. Comparative intrinsic and ANS fluorescence results of holo/apo-WT-hSOD1 and mutants indicated structural alterations in the local environment of tryptophan residue and hydrophobic patches, respectively. Experimental and MD data supported that substitution effect and metal deficiency of mutants (apo forms) in the dimer interface may promote the tendency to protein mis-folding and aggregation, consequently disrupting the dimer-monomer equilibrium and increased propensity to dissociation dimer into SOD-monomer ultimately leading to loss of stability and function. Overall, data analysis of apo/holo SOD1 forms on protein structure and function using computational and experimental studies will contribute to a better understanding of ALS pathogenicity.

A computational strategy for therapeutic development against superoxide dismutase (SOD1) amyloid formation: effect of polyphenols on the various events in the aggregation pathway

Pathology of superoxide dismutase 1 (SOD1) aggregation is linked to a neurodegenerative disease known as amyotrophic lateral sclerosis (ALS). Without suitable post-translational modifications (PTMs), the protein structure tends to become aggregation-prone. Understanding the role of PTMs and targeting the aggregation-prone SOD1 with small molecules can be used to design a strategy to inhibit its aggregation. Microsecond long molecular dynamics (MD) simulations followed by free energy surface (FES) analyses show that the loss of structure in the apo monomer happens locally and stepwise. Removing the disulfide bond from apoprotein leads to further instability in the zinc-binding loop, giving rise to non-native protein conformations. Further, it was found that these non-native conformations have a higher propensity to form a non-native dimer. We chose three structurally similar polyphenols based on their binding energies and investigated their impact on SOD1 aggregation kinetics. MD simulations of apo-SOD1^SH/corkscrew fibril-polyphenol complexes were also carried out. The effect of polyphenols was seen on fibril elongation as well. Based on the experiments and MD simulation results, it can be inferred that the choice of inhibitors is influenced not only by the binding energy but also by dimer interface stabilization, the proclivity to form non-native dimers, the propensity to break fibrils, and the propensity to decrease the rate of elongation. The polyphenols with 3' and 4' hydroxyl groups are better inhibitors of SOD1 aggregation.

Febrile temperatures modulate the formation of immune complexes relevant for autoimmune diseases

BACKGROUND

Autoimmune disorders encompass a diverse subset of diseases whose common symptoms include, among others, fever. Fever of unknown origins, once an infectious or tumor agent have been ruled out as possible causes, may originate with an autoimmune disease.

OBJECTIVE

To determine the role of febrile temperatures on the stability of antigens pertinent to autoimmunity, and on the immune complexes they form with commercial therapeutic monoclonal antibodies.

METHODS

Using molecular dynamics simulations, the binding between four antigens belonging to a set of autoimmune diseases and their individual monoclonal antibodies was investigated under different febrile temperatures.

RESULTS

It was determined that at febrile temperatures, monoclonal antibodies used in the therapy of autoimmune diseases bind with higher binding free energy to pertinent antigens, once the autoimmune condition has been established and treatment is warranted.

CONCLUSION

Performing molecular dynamics simulations at fever temperatures may be important for delineating the role antibodies may play in other diseases, including in cancers and infections.

Combined molecular docking and dynamics simulations studies of natural compounds as potent inhibitors against SARS-CoV-2 main protease

Main protease (Mpro) of SARS-CoV-2 is a key CoV enzyme that plays a pivotal role in mediating viral replication and transcription, making it an attractive drug target for SARS-CoV-2 the new strain of coronavirus. In this study, we evaluated biologically active compounds present in medicinal plants as potential SARS-CoV-2 Mpro inhibitors, using a molecular docking study with Autodock Vina software. Top seven compounds Afzelin, Phloroglucinol, Myricetin-3-O- rutinosid Tricin 7-neohesperidoside, Silybin, Kaempferol and Silychristin among 50 molecules of natural Origin (Algerian Medicinal plants) were selected which had better and significantly low binding energy as compared to the reference molecule with binding affinities of -9.3, -9.3, -9, -8.9, -8.5, 8.3 and -8.3 kcal mol^-1 respectively. Then, we analyzed the ADME properties of the best 7 ligands using the Web server SwissADME. Two of small molecules have been shown to be the ideal candidates for further drug development. Finally, the stability of the both compounds complexed with Mpro was validated through molecular dynamics (MD) simulation, they displayed stable trajectory (RMSD, RMSF) and molecular properties with consistent interaction profile in molecular dynamics simulations, moreover, Silybin could form more stable complex with Mpro than Silychristin.Communicated by Ramaswamy H. Sarma.

Amyloid fibrillation of the glaucoma associated myocilin protein is inhibited by epicatechin gallate (ECG)

Inherited glaucoma is a recent addition to the inventory of diseases arising due to protein misfolding. Mutations in the olfactomedin (OLF) domain of myocilin are the most common genetic cause behind this disease. Disease associated variants of m-OLF are predisposed to misfold and aggregate in the trabecular meshwork (TM) tissue of the eye. In recent years, the nature of these aggregates was revealed to exhibit the hallmarks of amyloids. Amyloid aggregates are highly stable structures that are formed, often with toxic consequences in a number of debilitating diseases. In spite of its clinical relevance the amyloidogenic nature of m-OLF has not been studied adequately. Here we have studied the amyloid fibrillation of m-OLF and report ECG as an inhibitor against it. Using biophysical and biochemical assays, coupled with advanced microscopic evaluations we show that ECG binds and stabilizes native m-OLF and thus prevents its aggregation into amyloid fibrils. Furthermore, we have used REMD simulations to delineate the stabilizing effects of ECG on the structure of m-OLF. Collectively, we report ECG as a molecular scaffold for designing and testing of novel inhibitors against m-OLF amyloid fibrillation.

Computer analysis of the relation between hydrogen bond stability in SOD1 mutants and the survival time of amyotrophic lateral sclerosis patients

BACKGROUND AND OBJECTIVE

Mutations in the SOD1 protein can lead to the death of motor neurons, which, in turn, causes an incurable disease called amyotrophic lateral sclerosis (ALS). At the same time, the mechanism of the onset and development of this disease is not fully understood and is often contradictory.

METHODS

Accelerated Molecular Dynamics as implemented in the OpenMM library, principal component analysis, regression analysis, random forest method.

RESULTS

The stability of hydrogen bonds in 72 mutants of the SOD1 protein was calculated. Principal component analysis was carried out. Based on ten principal components acting as predictors, a multiple linear regression model was constructed. An analysis of the correlation of these ten principal components with the initial values of the stability of hydrogen bonds made it possible to characterize the contribution of known structurally and functionally important sites in the SOD1 to the scatter of ALS patients' survival time.

CONCLUSION

Such an analysis made it possible to put forward hypotheses about the relationship between the stabilizing and destabilizing effects of mutations in different structurally and functionally important regions of SOD1 with the patients's survival time.

Effect of TMAO on the Structure and Phase Transition of Lipid Membranes: Potential Role of TMAO in Stabilizing Cell Membranes under Osmotic Stress

Extremophiles adopt strategies to deal with different environmental stresses, some of which are severely damaging to their cell membrane. To combat high osmotic stress, deep-sea organisms synthesize osmolytes, small polar organic molecules, like trimethylamine-N-oxide (TMAO), and incorporate them in the cell. TMAO is known to protect cells from high osmotic or hydrostatic pressure. Several experimental and simulation studies have revealed the roles of such osmolytes on stabilizing proteins. In contrast, the effect of osmolytes on the lipid membrane is poorly understood and broadly debated. A recent experiment has found strong evidence of the possible role of TMAO in stabilizing lipid membranes. Using the molecular dynamics (MD) simulation technique, we have demonstrated the effect of TMAO on two saturated fully hydrated lipid membranes in their fluid and gel phases. We have captured the impact of TMAO's concentration on the membrane's structural properties along with the fluid/gel phase transition temperatures. On increasing the concentration of TMAO, we see a substantial increase in the packing density of the membrane (estimated by area, thickness, and volume) and enhancement in the orientational order of lipid molecules. Having repulsive interaction with the lipid head group, the TMAO molecules are expelled away from the membrane surface, which induces dehydration of the lipid head groups, increasing the packing density. The addition of TMAO also increases the fluid/gel phase transition temperature of the membrane. All of these results are in close agreement with the experimental observations. This study, therefore, provides a molecular-level understanding of how TMAO can influence the cell membrane of deep-sea organisms and help in combating the osmotic stress condition.