Toxic Peptides Research Articles

Unraveling the power of peptides from Cucumaria frondosa coelomic fluid as multitarget therapy of diabetic kidney disease: An in-silico study

Diabetic kidney disease is a condition characterized by persistent albuminuria, diabetic glomerular lesions, and a reduced glomerular filtration rate in people with diabetes. Peptides in Cucumaria frondosa coelomic fluid have been proven to provide antidiabetic and anti-inflammatory activity that can be used as one of the innovations in developing a multitarget therapy, especially in diabetic kidney disease. Therefore, the aim of this study was to unravel the power of peptide-based metabolites from C. frondosa coelomic fluid as multitarget therapy for diabetic kidney disease using an in-silico study. UCSF Chimera software was utilized to construct the three-dimensional structure of coelomic fluid peptides from C. frondosa. The toxicity and allergenicity of peptides were examined using the ToxinPred and AllerTop websites, respectively. From the PDBJ database, the 3D structures of protein kinase B, alpha isoform (AKT1); vascular endothelial growth factor receptor 2 (VEGFR2); epidermal growth factor receptor (EGFR); α-glucosidase; and glucokinase were obtained. Molecular docking was carried out using MOE Software. In this in-silico study, peptide 9 (-10.32 kcal/mol), peptide 1 (-9.41 kcal/mol), and peptide 3 (-9.55 kcal/mol) were shown to act as specific adenosine triphosphate-competitive inhibitors of EGFR, AKT1, and VEGFR2, respectively. Peptide 8 (-11.06 kcal/mol) can specifically inhibit α-glucosidase by binding to its active site. Peptide 1 (-9.80 kcal/mol) is predicted to specifically inhibit glucokinase activity by blocking its active side. Molecular dynamics simulations confirmed stable interactions with receptor proteins. In conclusion, C. frondosa coelomic fluid peptides have been shown not only to alleviate diabetic kidney disease but also to stabilize blood glucose levels and prevent hyperglycemia based on in-silico analysis.

Bioinformatic investigation of Lytechinus variegatus coelomic fluid peptides as multiple oncogenic proteins inhibitors of colorectal cancer

Context: Colorectal cancer (CRC) remains a significant global health challenge despite advances in treatment modalities. The coelomic fluid of Lytechinus variegatus emerges as a rich source of bioactive peptides with the potential as a new therapeutic anticancer agent. Aims: To analyze the toxicity, allergenicity, and potential of L. variegatus coelomic fluid peptides as multitarget inhibitor agents of CRC cancer cells through an in silico study. Methods: Ten peptides from L. variegatus coelomic fluid were processed using UCSF Chimera software to model the three-dimensional structure. ToxinPred and AllerTop web servers were used to analyze the toxicity and allergenicity of peptides, respectively. The 3D structures of EGFR, AKT1, GSK3B, VEGFR2, and JAK3 were retrieved from the PDBJ database. MOE Software was used to perform molecular docking. Results: Peptide 4 binds to the ATP binding pocket of GSK3B protein with the strongest binding affinity value (-8,68 kcal/mol). The docking results between EGFR and peptides showed that peptide 10 binds to the ATP binding pocket with the lowest binding affinity (-9.52 kcal/mol). Peptide 2 binds to the ATP binding pocket of AKT1 with the lowest binding affinity value (-9.16 kcal/mol). Peptide 3 has the lowest binding affinity value of the JAK3 ATP binding pocket (-8,67 kcal/mol). Peptide 7 binds to the ATP binding pocket of VEGFR2 with the strongest binding affinity (-9,67 kcal/mol). Conclusions: The L. variegatus peptides have the potential as multitarget anti-CRC agents by inhibiting the activity of GSK3B, EGFR, AKT1, JAK3, and VEGFR2 proteins through the ATP competitive inhibitor action based on in silico study.

Evaluation of Novel HLM Peptide Activity and Toxicity against Planktonic and Biofilm Bacteria: Comparison to Standard Antibiotics.

Antibiotic resistance is one of the main concerns of public health, and the whole world is trying to overcome such a challenge by finding novel therapeutic modalities and approaches. This study has applied the sequence hybridization approach to the original sequence of two cathelicidin natural parent peptides (BMAP-28 and LL-37) to design a novel HLM peptide with broad antimicrobial activity. The physicochemical characteristics of the newly designed peptide were determined. As well, the new peptide's antimicrobial activity (Minimum Inhibitory Concentration (MIC), Minimum Bacterial Eradication Concentration (MBEC), and antibiofilm activity) was tested on two control (Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922) and two resistant (Methicillin-resistant Staphylococcus aureus (MRSA) ATCC BAA41, New Delhi metallo-beta- lactamase-1 Escherichia coli ATCC BAA-2452) bacterial strains. Furthermore, synergistic studies have been applied to HLM-hybridized peptides with five conventional antibiotics by checkerboard assays. Also, the toxicity of HLM-hybridized peptide was studied on Vero cell lines to obtain the IC50 value. Besides the percentage of hemolysis action, the peptide was tested in freshly heparinized blood. The MIC values for the HLM peptide were obtained as 20, 10, 20, and 20 μM, respectively. Also, the results showed no hemolysis action, with low to slightly moderate toxicity action against mammalian cells, with an IC50 value of 10.06. The Biomatik corporate labs, where HLM was manufactured, determined the stability results of the product by Mass Spectrophotometry (MS) and High-performance Liquid Chromatography (HPLC) methods. The HLM-hybridized peptide exhibited a range of synergistic to additive antimicrobial activities upon combination with five commercially available different antibiotics. It has demonstrated the biofilm-killing effects in the same concentration required to eradicate the control strains. The results indicated that HLM-hybridized peptide displayed a broad-spectrum activity toward different bacterial strains in planktonic and biofilm forms. It showed synergistic or additive antimicrobial activity upon combining with commercially available different antibiotics.

Tumor-Specific Protein Induced in Situ Self-Assembly of Peptide Drugs for Synergistic Mitochondria Disruption.

Mitochondria-targeted cancer therapy is an effective method for controlling tumor growth. However, the presence of repair mechanisms in tumor cells in response to mitochondrial damage poses significant challenges for treatment. By taking advantage of intracellular self-assembly technology, a peptide nanomaterial, RC-K-FX, that enters tumor cells in a monomeric form is designed. After binding to MUC1-C inside the cell membrane, RC-K-FX assembles into a spherical structure that stably encapsulates MUC1-C, inhibiting its dimerization and blocking the repair of stress-induced mitochondrial damage in tumor cells. Moreover, the self-assembled mitochondrial toxic peptide effectively destroys the mitochondria, and the loss of mitochondrial repair significantly increases tumor cytotoxicity by disrupting the redox balance, enhancing reactive oxygen species (ROS), inhibiting the nuclear factor (NF)-κB pathway, and suppressing the epithelial-mesenchymal transition (EMT) process. After intravenous administration, RC-G-FX accumulated at the tumor site, exhibiting improved anti-tumor effects and extending the overall survival of tumor-bearing mice. Therefore, the integration of the in situ self-assembly of peptide drugs and damage to mitochondrial repair mechanisms provides effective therapeutic options for malignancy.

In silico analysis of Arbacia lixula-derived peptides and plasmid construction for recombinant anti-aging therapies.

Skin aging is one of the degenerative processes influenced by tyrosinase, elastase, collagenase, hyaluronidase, and matrix metalloproteinase-9 (MMP9) activity. One promising avenue for discovering antiaging therapeutics is the peptides from the Arbacia lixula spine. The aim of this study was to explore the potential of peptides from A. lixula spine as a multitarget inhibitor for recombinant antiaging therapies through in silico approaches. The crystal structure of peptides previously identified in A. lixula spine was visualized using the UCSF Chimera. The protein data bank (PDB) database was used to obtain the crystal structures of protein targets. The webservers Innovagen, AllerTop, and ToxinPred were utilized to predict the peptide's water solubility, toxicity, and allergenicity. MOE application was used to prepare all ligands and proteins, molecular docking, and visualization. Molecular dynamics simulations were carried out on the protein-ligand complexes on Yasara Dynamics application. The Benchling website was used to perform virtual electrophoresis and reconstruct the recombinant plasmid (Psb1c3). Based on the molecular docking results, peptide REGSPDLLE has the potential as a multitarget inhibitor of tyrosinase (-9.07 kcal/mol), hyaluronidase (-10.57 kcal/mol), elastase (-9.32 kcal/mol), collagenase (-10.57 kcal/mol), and MMP9 (-10.43 kcal/mol). Peptide REGSPDLLE was selected due to its strong binding affinity on the active site of each target protein and exhibits non-toxic, non-allergenic, and good water-soluble as indicated by Support Vector Machine score <0. Molecular dynamics simulations confirmed stable interactions with receptor proteins. Peptide REGSPDLLE was successfully inserted into the recombinant pSB1C3 plasmid, confirmed by virtual electrophoresis with bands at ∼2000bp and ∼150 bp. Further in vitro and in vivo studies are necessary to verify the anti- aging efficacy of peptide REGSPDLLE.

Impact of sodium dodecyl sulfate, cetyltrimethylammonium chloride and octyl glucoside surfactants on Aβ dimer conformations: A multiscale approach with MD simulations

This research investigates the effects of an anionic surfactant, sodium dodecyl sulfate (SDS), a cationic surfactant, cetyltrimethylammonium chloride (CTAC), and a nonionic surfactant, octyl glucoside (OG), on the conformation of beta-amyloid peptide dimer using molecular dynamics simulations to decipher the molecular mechanisms underlying these interactions and their effects on Aβ aggregation and toxicity in Alzheimer’s disease. Four simulation models were crafted, each housing a beta-amyloid peptide dimer, with three models incorporating 60 CTAC, 80 SDS, and 50 OG molecules to surpass the critical micelle concentration. Key findings include significant impacts of SDS, CTAC, and OG on the conformational dynamics of Aβ peptides as evidenced by RMSD and RMSF analyses. SDS notably increased the RMSF of residues 1–10 and had a pronounced effect on the C-termini, disrupting the critical salt bridge between aspartic acid 23 and lysine 28, associated with reduced peptide toxicity. Additionally, SDS disrupted more hydrogen bonds and hydrophobic interactions between the monomers of the Aβ dimer, predominantly in the C-termini region. Free Energy Landscape analysis revealed significant structural changes in the Aβ dimer in the presence of surfactants, with varying distributions of surfactant aggregates. Binding free energy calculations using MM-PBSA demonstrated that SDS exhibited the strongest binding affinity to the Aβ dimer, followed by CTAC and OG, with electrostatic forces playing a pivotal role. These outcomes align with experimental data, suggesting that SDS and CTAC, at concentrations above the CMC, diminish Aβ peptide aggregation and toxicity, whereas OG marginally increases toxicity.

Stereorandomized Oncocins with Preserved Ribosome Binding and Antibacterial Activity.

We recently showed that solid-phase peptide synthesis using racemic amino acids yields stereorandomized peptides comprising all possible diastereomers as homogeneous, single-mass products that can be purified by HPLC and that stereorandomization modulates activity, toxicity, and stability of membrane-disruptive cyclic and linear antimicrobial peptides (AMPs) and dendrimers. Here, we tested if stereorandomization might be compatible with target binding peptides with the example of the proline-rich AMP oncocin, which inhibits the bacterial ribosome. Stereorandomization of up to nine C-terminal residues preserved ribosome binding and antibacterial effects including activities against drug-resistant bacteria and protected against serum degradation. Surprisingly, fully stereorandomized oncocin was as active as L-oncocin in dilute growth media stimulating peptide uptake, although it did not bind the ribosome, indicative of an alternative mechanism of action. These experiments show that stereorandomization can be compatible with target binding peptides and can help understand their mechanism of action.

Machine Learning Framework for Conotoxin Class and Molecular Target Prediction.

Conotoxins are small and highly potent neurotoxic peptides derived from the venom of marine cone snails which have captured the interest of the scientific community due to their pharmacological potential. These toxins display significant sequence and structure diversity, which results in a wide range of specificities for several different ion channels and receptors. Despite the recognized importance of these compounds, our ability to determine their binding targets and toxicities remains a significant challenge. Predicting the target receptors of conotoxins, based solely on their amino acid sequence, remains a challenge due to the intricate relationships between structure, function, target specificity, and the significant conformational heterogeneity observed in conotoxins with the same primary sequence. We have previously demonstrated that the inclusion of post-translational modifications, collisional cross sections values, and other structural features, when added to the standard primary sequence features, improves the prediction accuracy of conotoxins against non-toxic and other toxic peptides across varied datasets and several different commonly used machine learning classifiers. Here, we present the effects of these features on conotoxin class and molecular target predictions, in particular, predicting conotoxins that bind to nicotinic acetylcholine receptors (nAChRs). We also demonstrate the use of the Synthetic Minority Oversampling Technique (SMOTE)-Tomek in balancing the datasets while simultaneously making the different classes more distinct by reducing the number of ambiguous samples which nearly overlap between the classes. In predicting the alpha, mu, and omega conotoxin classes, the SMOTE-Tomek PCA PLR model, using the combination of the SS and P feature sets establishes the best performance with an overall accuracy (OA) of 95.95%, with an average accuracy (AA) of 93.04%, and an f1 score of 0.959. Using this model, we obtained sensitivities of 98.98%, 89.66%, and 90.48% when predicting alpha, mu, and omega conotoxin classes, respectively. Similarly, in predicting conotoxins that bind to nAChRs, the SMOTE-Tomek PCA SVM model, which used the collisional cross sections (CCSs) and the P feature sets, demonstrated the highest performance with 91.3% OA, 91.32% AA, and an f1 score of 0.9131. The sensitivity when predicting conotoxins that bind to nAChRs is 91.46% with a 91.18% sensitivity when predicting conotoxins that do not bind to nAChRs.

The structure of an amyloid precursor protein/talin complex indicates a mechanical basis of Alzheimer's disease.

Misprocessing of amyloid precursor protein (APP) is one of the major causes of Alzheimer's disease. APP comprises a large extracellular region, a single transmembrane helix and a short cytoplasmic tail containing an NPxY motif (normally referred to as the YENPTY motif). Talins are synaptic scaffold proteins that connect the cytoskeletal machinery to the plasma membrane via binding NPxY motifs in the cytoplasmic tail of integrins. Here, we report the crystal structure of an APP/talin1 complex identifying a new way to couple the cytoskeletal machinery to synaptic sites through APP. Proximity ligation assay (PLA) confirmed the close proximity of talin1 and APP in primary neurons, and talin1 depletion had a dramatic effect on APP processing in cells. Structural modelling reveals APP might form an extracellular meshwork that mechanically couples the cytoskeletons of the pre- and post-synaptic compartments. We propose APP processing represents a mechanical signalling pathway whereby under tension, the cleavage sites in APP have varying accessibility to cleavage by secretases. This leads us to propose a new hypothesis for Alzheimer's, where misregulated APP dynamics result in loss of the mechanical integrity of the synapse, corruption and loss of mechanical binary data, and excessive generation of toxic plaque-forming Aβ42 peptide.

Effective combinations of silver nanoparticles and antimicrobial peptides against antibiotic-resistant bacteria

BACKGROUND: The problem of constantly growing resistance of microorganisms to the antibiotics used forces scientists to constantly search for new antimicrobial agents. AIM: To study the antimicrobial activity and toxicity of silver nanoparticles and antimicrobial peptides with a β-hairpin structure, and to characterize their combined antimicrobial action. MATERIALS AND METHODS: The antimicrobial activity of silver nanoparticles and antimicrobial peptides against antibiotic-resistant bacteria was assessed by serial dilutions in a liquid nutrient medium, and the combined antimicrobial activity – by serial dilutions according to the “checkerboard” method. The toxicity of the substances to human cells was determined using a hemolytic test. RESULTS: The studied silver nanoparticles have pronounced antimicrobial activity and low toxicity to human erythrocytes. Silver nanoparticles containing acetylcysteine are more active against gram-negative bacteria than against gram-positive ones. Synergism of the antibacterial action was detected with the combined use of silver nanoparticles stabilized with sodium oleate and protegrin-1. A synergistic antimicrobial effect was also noted for combinations of silver nanoparticles containing acetylcysteine with protegrin-1, ricaecilin and shuchin-4. CONCLUSIONS: Effective combinations of silver nanoparticles and antimicrobial peptides have been identified that act synergistically against antibiotic-resistant bacterial strains, i.e. they multiply the effect of each other. These combinations can be used as prototypes for the development of antibacterial drugs.

Venomous Peptides: Molecular Origin of the Toxicity of Snake Venom PLA2-like Peptides.

Snakebite envenoming claims 81-138 thousand lives annually, with vipers responsible for many of those. Phospholipase A2 (PLA2) enzymes and PLA2-like proteins are among the most important viper venom toxins. The latter are particularly intriguing, as three decades after their discovery, their molecular mechanism of toxicity is still poorly understood at best. PLA2-like proteins destabilize eukaryotic cell membranes through an unknown mechanism, causing an uncontrolled influx of Ca2+ ions and ultimately triggering cell death. It is now clear that the C-terminal segment is fundamental to the toxicity, as 13-mer peptides with the same sequence exhibit most or all of the activities of the complete PLA2-like proteins. To finally clarify the mechanism of toxicity of these venom peptides, we have simulated their interaction with model cell membranes. Molecular dynamics simulations showed that peptides initially dispersed across the cell membrane quickly and spontaneously migrated, aggregated, induced membrane thinning, and formed clear and transient membrane pores. We calculated the potentials of the mean force for Ca2+ transfer across the cell membranes through the transient pores. The pores significantly lower the free energy barrier for Ca2+ translocation, an effect that grows with the size of the peptide aggregates and, thus, with the pore radius. Ca2+ flowed across the membrane through the largest pores with almost no barrier. The permeability of Ca2+ through the largest pores exceeded the permeability of pharmaceutical drugs by 4 orders of magnitude, revealing the easiness by which Ca2+ overflows the intracellular medium. These results elucidate the illusive molecular origin of the toxicity of this famous class of snake venom-derived peptides.

Beta-Amyloid and Its Asp7 Isoform: Morphological and Aggregation Properties and Effects of Intracerebroventricular Administration.

One of the hallmarks of Alzheimer's disease (AD) is the accumulation of aggregated beta-amyloid (Aβ) protein in the form of senile plaques within brain tissue. Senile plaques contain various post-translational modifications of Aβ, including prevalent isomerization of Asp7 residue. The Asp7 isomer has been shown to exhibit increased neurotoxicity and induce amyloidogenesis in brain tissue of transgenic mice. The toxicity of Aβ peptides may be partly mediated by their structure and morphology. In this respect, in this study we analyzed the structural and aggregation characteristics of the Asp7 isoform of Aβ42 and compared them to those of synthetic Aβ42. We also investigated the effects of intracerebroventricular (i.c.v.) administration of these peptides, a method often used to induce AD-like symptoms in rodent models. Atomic force microscopy (AFM) was conducted to compare the morphological and aggregation properties of Aβ42 and Asp7 iso-Aβ42. The effects of i.c.v. stereotaxic administration of the proteins were assessed via behavioral analysis and reactive oxygen species (ROS) estimation in vivo using a scanning ion-conductance microscope with a confocal module. AFM measurements revealed structural differences between the two peptides, most notably in their soluble toxic oligomeric forms. The i.c.v. administration of Asp7 iso-Aβ42 induced spatial memory deficits in rats and elevated oxidative stress levels in vivo, suggesting a potential of ROS in the pathogenic mechanism of the peptide. The findings support the further investigation of Asp7 iso-Aβ42 in translational research on AD and suggest its involvement in neurodegenerative processes.

Phosphorylation as an Effective Tool to Improve Stability and Reduce Toxicity of Antimicrobial Peptides.

Developing a straightforward and effective strategy to modify antimicrobial peptides (AMPs) is crucial in overcoming the challenges posed by their instability and toxicity. Phosphorylation can reduce toxicity and improve the stability of AMPs. Based on these, we designed a series of peptides and their corresponding phosphorylated forms. The results showed that all phosphorylated peptides displayed reduced toxicity and enhanced stability compared to their unphosphorylated counterparts. Among them, W3BipY8-P stood out as the most promising peptide, exhibiting similar antibacterial activity as its unphosphorylated analog W3BipY8 but with significantly reduced hemolytic activity (19-fold decrease), cytotoxicity (3.3-fold decrease), and an extended serum half-life 6.3 times longer than W3BipY8. W3BipY8-P exerted bactericidal effects by disrupting bacterial membranes. Notably, W3BipY8-P significantly prolonged the survival of bacteria-infected animals while its LD50 was 4.2 times higher than that of W3BipY8. These findings highlight phosphorylation as an effective strategy for improving the antimicrobial properties of AMPs.

Segment-Based Peptide Design Reveals the Importance of N-Terminal High Cationicity for Antimicrobial Activity Against Gram-Negative Pathogens.

Host defense antimicrobial peptides (AMPs) are recognized candidates to develop a new generation of peptide antibiotics. While high hydrophobicity can be deployed in peptides for eliminating Gram-positive bacteria, high cationicity is usually observed in AMPs against Gram-negative pathogen. This study investigates how the sequence distribution of basic amino acids affects peptide activity. For this purpose, we utilized human cathelicidin LL-37 as a template and designed four highly selective ultrashort peptides with similar length, net charge, and hydrophobic content. LL-10 + , RK-9 + , KR-8 + , and RIK-10 + showed similar activity against methicillin-resistant Staphylococcus aureus in vitro and comparable antibiofilm efficacy in a murine wound model. However, these peptides showed clear activity differences against Gram-negative pathogens with RIK-10 + (i.e., LL-37mini2) being the strongest and LL-10 + the weakest. To understand this activity difference, we characterized peptide toxicity; the effects of salts, pH, and serum on peptide activity; and the mechanism of action and determined the membrane-bound helical structure for RIK-10 + by two-dimensional NMR spectroscopy. By writing an R program, we generated charge density plots for these peptides and uncovered the importance of the N-terminal high-density basic charges for antimicrobial potency. To validate this finding, we reversed the sequences of two peptides. Interestingly, sequence reversal weakened the activity of RIK-10 + but increased the activity of LL-10 + especially against Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii. Those more active peptides with high cationicity at the N-terminus are also more hydrophobic based on HPLC retention times. A database search found numerous natural sequences that arrange basic amino acids primarily at the N-terminus. Combined, this study not only obtained novel peptide leads but also discovered one useful strategy for designing novel antimicrobials to control drug-resistant Gram-negative pathogens.

ToxGIN: an In silico prediction model for peptide toxicity via graph isomorphism networks integrating peptide sequence and structure information.

Peptide drugs have demonstrated enormous potential in treating a variety of diseases, yet toxicity prediction remains a significant challenge in drug development. Existing models for prediction of peptide toxicity largely rely on sequence information and often neglect the three-dimensional (3D) structures of peptides. This study introduced a novel model for short peptide toxicity prediction, named ToxGIN. The model utilizes Graph Isomorphism Network (GIN), integrating the underlying amino acid sequence composition and the 3D structures of peptides. ToxGIN comprises three primary modules: (i) Sequence processing module, converting peptide 3D structures and sequences into information of nodes and edges; (ii) Feature extraction module, utilizing GIN to learn discriminative features from nodes and edges; (iii) Classification module, employing a fully connected classifier for toxicity prediction. ToxGIN performed well on the independent test set with F1 score = 0.83, AUROC = 0.91, and Matthews correlation coefficient = 0.68, better than existing models for prediction of peptide toxicity. These results validated the effectiveness of integrating 3D structural information with sequence data using GIN for peptide toxicity prediction. The proposed ToxGIN and data can be freely accessible at https://github.com/cihebiyql/ToxGIN.

Host Tropism and Structural Biology of ABC Toxin Complexes.

ABC toxin complexes are a class of protein toxin translocases comprised of a multimeric assembly of protein subunits. Each subunit displays a unique composition, contributing to the formation of a syringe-like nano-machine with natural cargo carrying, targeting, and translocation capabilities. Many of these toxins are insecticidal, drawing increasing interest in agriculture for use as biological pesticides. The A subunit (TcA) is the largest subunit of the complex and contains domains associated with membrane permeation and targeting. The B and C subunits, TcB and TcC, respectively, package into a cocoon-like structure that contains a toxic peptide and are coupled to TcA to form a continuous channel upon final assembly. In this review, we outline the current understanding and gaps in the knowledge pertaining to ABC toxins, highlighting seven published structures of TcAs and how these structures have led to a better understanding of the mechanism of host tropism and toxin translocation. We also highlight similarities and differences between homologues that contribute to variations in host specificity and conformational change. Lastly, we review the biotechnological potential of ABC toxins as both pesticides and cargo-carrying shuttles that enable the transport of peptides into cells.

Molecular Integrative Study on Inhibitory Effects of Pentapeptides on Polymerization and Cell Toxicity of Amyloid-β Peptide (1-42).

Alzheimer's Disease (AD) is a multifaceted neurodegenerative disease predominantly defined by the extracellular accumulation of amyloid-β (Aβ) peptide. In light of this, in the past decade, several clinical approaches have been used aiming at developing peptides for therapeutic use in AD. The use of cationic arginine-rich peptides (CARPs) in targeting protein aggregations has been on the rise. Also, the process of peptide development employing computational approaches has attracted a lot of attention recently. Using a structure database containing pentapeptides made from 20 L-α amino acids, we employed molecular docking to sort pentapeptides that can bind to Aβ42, then performed molecular dynamics (MD) analyses, including analysis of the binding stability, interaction energy, and binding free energy to screen ligands. Transmission electron microscopy (TEM), circular dichroism (CD), thioflavin T (ThT) fluorescence detection of Aβ42 polymerization, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay, and the flow cytometry of reactive oxygen species (ROS) were carried out to evaluate the influence of pentapeptides on the aggregation and cell toxicity of Aβ42. Two pentapeptides (TRRRR and ARRGR) were found to have strong effects on inhibiting the aggregation of Aβ42 and reducing the toxicity of Aβ42 secreted by SH-SY5Y cells, including cell death, reactive oxygen species (ROS) production, and apoptosis.

Autophagy-lysosomal-associated neuronal death in neurodegenerative disease.

Autophagy, the major lysosomal pathway for degrading damaged or obsolete constituents, protects neurons by eliminating toxic organelles and peptides, restoring nutrient and energy homeostasis, and inhibiting apoptosis. These functions are especially vital in neurons, which are postmitotic and must survive for many decades while confronting mounting challenges of cell aging. Autophagy failure, especially related to the declining lysosomal ("phagy") functions, heightens the neuron's vulnerability to genetic and environmental factors underlying Alzheimer's disease (AD) and other late-age onset neurodegenerative diseases. Components of the global autophagy-lysosomal pathway and the closely integrated endolysosomal system are increasingly implicated as primary targets of these disorders. In AD, an imbalance between heightened autophagy induction and diminished lysosomal function in highly vulnerable pyramidal neuron populations yields an intracellular lysosomal build-up of undegraded substrates, including APP-βCTF, an inhibitor of lysosomal acidification, and membrane-damaging Aβ peptide. In the most compromised of these neurons, β-amyloid accumulates intraneuronally in plaque-like aggregates that become extracellular senile plaques when these neurons die, reflecting an "inside-out" origin of amyloid plaques seen in human AD brain and in mouse models of AD pathology. In this review, the author describes the importance of lysosomal-dependent neuronal cell death in AD associated with uniquely extreme autophagy pathology (PANTHOS) which is described as triggered by lysosomal membrane permeability during the earliest "intraneuronal" stage of AD. Effectors of other cell death cascades, notably calcium-activated calpains and protein kinases, contribute to lysosomal injury that induces leakage of cathepsins and activation of additional death cascades. Subsequent events in AD, such as microglial invasion and neuroinflammation, induce further cytotoxicity. In major neurodegenerative disease models, neuronal death and ensuing neuropathologies are substantially remediable by reversing underlying primary lysosomal deficits, thus implicating lysosomal failure and autophagy dysfunction as primary triggers of lysosomal-dependent cell death and AD pathogenesis and as promising therapeutic targets.

Cyanobacterial Cyclic Peptides Can Disrupt Cytoskeleton Organization in Human Astrocytes-A Contribution to the Understanding of the Systemic Toxicity of Cyanotoxins.

The systemic toxicity of cyclic peptides produced by cyanobacteria (CCPs) is not yet completely understood. Apart from the most known damages to the liver and kidneys, symptoms of their neurotoxicity have also been reported. Hepatotoxic CCPs, like microcystins, as well as non-hepatotoxic anabaenopeptins and planktopeptins, all exhibit cytotoxic and cytostatic effects on mammalian cells. However, responses of different cell types to CCPs depend on their specific modes of interaction with cell membranes. This study demonstrates that non-hepatotoxic planktopeptin BL1125 and anabaenopeptins B and F, at concentrations up to 10 µM, affect normal and tumor human astrocytes (NHA and U87-GM) in vitro by their almost immediate insertion into the lipid monolayer. Like microcystin-LR (up to 1 µM), they inhibit Ser/Thr phosphatases and reorganize cytoskeletal elements, with modest effects on their gene expression. Based on the observed effects on intermediate filaments and intermediate filament linkage elements, their direct or indirect influence on tubulin cytoskeletons via post-translational modifications, we conclude that the basic mechanism of CCP toxicities is the induction of inter- and intracellular communication failure. The assessed inhibitory activity on Ser/Thr phosphatases is also crucial since the signal transduction cascades are modulated by phosphorylation/dephosphorylation processes.

Activity of Membrane-Permeabilizing Lpt Peptides.

Herein, we investigated the toxicity and membrane-permeabilizing capabilities of Lpt and Lpt-like peptides, belonging to type I toxin-antitoxin systems carried by plasmid DNA of Lacticaseibacillus strains. These 29 amino acid peptides are predicted to form α-helical structures with a conserved central hydrophobic sequence and differently charged hydrophilic termini. Like Lpt, the expression of Lpt-like in E. coli induced growth arrest, nucleoid condensation, and cell membrane damage, suggesting membrane interaction as the mode of action. The membrane permeabilization activity of both peptides was evaluated by using liposome leakage assays, dynamic light scattering, and CD spectroscopy. Lpt and Lpt-like showed liposome leakage activity, which did not lead to liposome disruption but depended on peptide concentration. Lpt was generally more effective than Lpt-like, probably due to different physical chemical properties. Leakage was significantly reduced in larger liposomes and increased with negatively charged PCPS liposomes, indicating that electrostatic interactions and membrane curvature influence peptide activity. Contrary to most membrane-active peptides, Lpt an Lpt-like progressively lost their α-helical structure upon interaction with liposomes. Our data are inconsistent with the formation of membrane-spanning peptide pores but support a mechanism relying on the transient failure of the membrane permeability barrier possibly through the formation of "lipid pores".