Polyarginine Interacts More Strongly and Cooperatively than Polylysine with Phospholipid Bilayers

Assessing nanoparticle-enabled dsRNA delivery for oral RNAi in two orthopteran pests: Schistocerca gregaria and Melanoplus sanguinipes

Locusts and pest grasshoppers (Orthoptera: Acrididae) cause significant economic losses to agricultural crops and rangeland forage and can even cause humanitarian crises during periodic plagues. Current management methods for these insects rely heavily on broad-spectrum chemical insecticides and growth regulators, which can affect non-target organisms and may eventually develop resistance in the targeted species. Therefore, we assessed the potential of RNA interference (RNAi)-based alternative strategies that could supplement the current management methods. In insects, RNAi efficiency is known to vary with the method of double-stranded RNA (dsRNA) delivery. In this study, we tested two different delivery methods (injection and oral feeding) in the desert locust (Schistocerca gregaria) and the migratory grasshopper (Melanoplus sanguinipes) and showed that both species are sensitive to the injection but not to the oral feeding of dsRNA, likely due to high nuclease activity or poor uptake in the midgut. To address these limitations, we explored the utility of using nanoparticles that are often used for drug delivery in humans as a carrier (poly lactic-co-glycolic acid [PLGA] and poly(L-arginine)-polyethylene glycol [PLA-PEG]) for orally delivering dsRNA to the insect pests. Although the PLGA nanoparticles successfully permeated the digestive system into the hemolymph and the PLA-PEG-dsRNA complexes remained stable in the midgut juice and were detected in the fat body, neither dsRNA-encapsulating nanoparticle elicited gene knockdown upon oral feeding. These results suggest that nanoparticle-based oral delivery improves dsRNA stability and midgut permeation. However, additional barriers must be overcome to achieve efficient oral RNAi in these orthopteran pest species.

Affinity-Based Isolation and One-Pot Analysis of Extracellular Vesicles from Biofluids Using Phase Separated Zwitterionic Coacervates

Extracellular vesicles (EVs) hold promise for liquid biopsy and drug delivery applications. However, their heterogeneous nature poses challenges for efficient and selective isolation from complex biofluids. Here, an isolation method based on phase-separated zwitterionic (ZW) coacervates is developed. These coacervates form over a wide range of pH values and ionic strengths, ensuring compatibility with all biofluids. They exhibit antifouling properties that minimize nonspecific binding, allowing for the selective isolation of EVs from biofluids upon functionalization of the polymer with a suitable affinity probe, as proved here with a membrane-sensing peptide. This strategy is applied to pull down, concentrate, and release EVs from urine samples with high yields while retaining their structural integrity. This approach effectively separates EVs from lipoproteins, a challenging task for conventional separation techniques. The power of the approach is demonstrated as a preparative step for downstream analysis and as a one-pot assay to profile EV biomarkers in complex fluids. The latter application, implemented here with flow cytometry, significantly streamlines pre-analytical workflows. Thus, functionalized ZW coacervates represent an effective strategy for the selective isolation and direct analysis of EVs from complex mixtures, paving the way for advances in large-scale manufacturing and diagnostics.

The acidic latex protein from Hevea brasiliensis serves as an anionic antimicrobial peptide

Background

Hev b5 is a unique acidic protein identified as an allergen in natural latex and latex gloves, known for stimulating histamine release from human basophils sensitized with serum from latex-allergic individuals. It is rich in glutamic acid and proline residues arranged in repeated motifs. The protein's unusual amino acid composition includes 48% negatively charged residues and 13% positively charged residues.

Methods

The recombinant form of Hev b5 (rHev b5) was produced in Escherichia coli. Its chitinase activity, which may provide antifungal properties by breaking down chitin in phytopathogen cell walls, was assessed. Additionally, the antibacterial activity of rHev b5 against Gram-positive and Gram-negative bacteria, including Bacillus cereus, Staphylococcus aureus, E. coli and Salmonella typhi, was evaluated. The potential enhancement of this activity in the presence of calcium or zinc ions was investigated to understand the underlying mechanism involving binding to microbial membranes via metal ion-mediated cationic salt bridges.

Results

rHev b5 exhibited significant chitinase activity and demonstrated substantial antibacterial effects against both Gram-positive and Gram-negative bacteria. The antibacterial activity was notably enhanced in the presence of zinc or calcium ions, suggesting that rHev b5 binds to microbial membranes through metal ion-mediated cationic salt bridges, leading to cell lysis and microbial death.

Conclusion

Antimicrobial properties and chitinase activity of Hev b5 underline its potential as an anionic antimicrobial peptide, offering both antifungal and antibacterial defenses. These findings position Hev b5 as a promising candidate for further research in antimicrobial peptide applications.

Strategies for the design of biomimetic cell-penetrating peptides using AI-driven in silico tools for drug delivery

Cell-penetrating peptides (CPP) have gained rapid attention over the last 25 years; this is attributed to their versatility, customisation, and 'Trojan horse' delivery that evades the immune system. However, the current CPP rational design process is limited, as it requires several rounds of peptide synthesis, prediction and wet-lab validation, which is expensive, time-consuming and requires extensive knowledge in peptide chemistry. Artificial intelligence (AI) has emerged as a promising alternative which can augment the design process, for example by determining physiochemical characteristics, secondary structure, solvent accessibility, disorder and flexibility, as well as predicting in vivo behaviour such as toxicity and peptidase degradation. Other more recent tools utilise supervised machine learning (ML) to predict the penetrative ability of an amino acid sequence. The use of AI in the CPP design process has the potential to reduce development costs and increase the chances of success with respect to delivery. This review provides a survey of in silico tools and AI platforms which can be utilised in the design process, and the key features that should be taken into consideration when designing next generation CPPs.

Low-complexity regions in fungi display functional groups and are depleted in positively charged amino acids

Reports on the diversity and occurrence of low-complexity regions (LCR) in Eukaryota are limited. Some studies have provided a more extensive characterization of LCR proteins in prokaryotes. There is a growing body of knowledge about a plethora of biological functions attributable to LCRs. However, it is hard to determine to what extent observed phenomena apply to fungi since most studies of fungal LCRs were limited to model yeasts. To fill this gap, we performed a survey of LCRs in proteins across all fungal tree of life branches. We show that the abundance of LCRs and the abundance of proteins with LCRs are positively correlated with proteome size. We observed that most LCRs are present in proteins with protein domains but do not overlap with the domain regions. LCRs are associated with many duplicated protein domains. The quantity of particular amino acids in LCRs deviates from the background frequency with a clear over-representation of amino acids with functional groups and a negative charge. Moreover, we discovered that each lineage of fungi favors distinct LCRs expansions. Early diverging fungal lineages differ in LCR abundance and composition pointing at a different evolutionary trajectory of each fungal group.

Polyproline-Polyornithine Diblock Copolymers with Inherent Mitochondria Tropism

Mitochondria play critical roles in regulating cell fate, with dysfunction correlating with the development of multiple diseases, emphasizing the need for engineered nanomedicines that cross biological barriers. Said nanomedicines often target fluctuating mitochondrial properties and/or present inefficient/insufficient cytosolic delivery (resulting in poor overall activity), while many require complex synthetic procedures involving targeting residues (hindering clinical translation). The synthesis/characterization of polypeptide-based cell penetrating diblock copolymers of poly-L-ornithine (PLO) and polyproline (PLP) (PLOn-PLPm, n:m ratio 1:3) are described as mitochondria-targeting nanocarriers. Synthesis involves a simple two-step methodology based on N-carboxyanhydride ring-opening polymerization, with the scale-up optimization using a "design of experiments" approach. The molecular mechanisms behind targetability and therapeutic activity are investigated through physical/biological processes for diblock copolymers themselves or as targeting moieties in a poly-L-glutamic (PGA)-based conjugate. Diblock copolymers prompt rapid cell entry via energy-independent mechanisms and recognize mitochondria through the mitochondria-specific phospholipid cardiolipin (CL). Stimuli-driven conditions and mitochondria polarization dynamics, which decrease efficacy depending on disease type/stage, do not compromise diblock copolymer uptake/targetability. Diblock copolymers exhibit inherent concentration-dependent anti-tumorigenic activity at the mitochondrial level. The diblock copolymer conjugate possesses improved safety, significant cell penetration, and mitochondrial accumulation via cardiolipin recognition. These findings may support the development of efficient and safe mitochondrial-targeting nanomedicines.

Boosting Lipofection Efficiency Through Enhanced Membrane Fusion Mechanisms

Gene transfection is a fundamental technique in the fields of biological research and therapeutic innovation. Due to their biocompatibility and membrane-mimetic properties, lipid vectors serve as essential tools in transfection. The successful delivery of genetic material into the cytoplasm is contingent upon the fusion of the vector and cellular membranes, which enables hydrophilic polynucleic acids to traverse the hydrophobic barriers of two intervening membranes. This review examines the critical role of membrane fusion in lipofection efficiency, with a particular focus on the molecular mechanisms that govern lipoplex-membrane interactions. This analysis will examine the key challenges inherent to the fusion process, from achieving initial membrane proximity to facilitating final content release through membrane remodeling. In contrast to viral vectors, which utilize specialized fusion proteins, lipid vectors necessitate a strategic formulation and environmental optimization to enhance their fusogenicity. This review discusses recent advances in vector design and fusion-promoting strategies, emphasizing their potential to improve gene delivery yield. It highlights the importance of understanding lipoplex-membrane fusion mechanisms for developing next-generation delivery systems and emphasizes the need for continued fundamental research to advance lipid-mediated transfection technology.

Molecular dynamics simulations unveil the aggregation patterns and salting out of polyarginines at zwitterionic POPC bilayers in solutions of various ionic strengths

This study employs molecular dynamics (MD) simulations to investigate the adsorption and aggregation behavior of simple polyarginine cell-penetrating peptides (CPPs), specifically modeled as R9 peptides, at zwitterionic phosphocholine POPC membranes under varying ionic strengths of two peptide concentrations and two concentrations of NaCl and CaCl2. The results reveal an intriguing phenomenon of R9 aggregation at the membrane, which is dependent on the ionic strength, indicating a salting-out effect. As the peptide concentration and ionic strength increase, peptide aggregation also increases, with aggregate lifetimes and sizes showing a corresponding rise, accompanied by the total decrease of adsorbed peptides at the membrane surface. Notably, in high ionic strength environments, large R9 aggregates, such as octamers, are also observed occasionally. The salting-out, typically uncommon for short positively charged peptides, is attributed to the unique properties of arginine amino acid, specifically by its side chain containing amphiphilic guanidinium (Gdm+) ion which makes both intermolecular hydrophobic like-charge Gdm+ - Gdm+ and salt-bridge Gdm+ - C-terminus interactions, where the former are increased with the ionic strength, and the latter decreased due to electrostatic screening. The aggregation behavior of R9 peptides at membranes can also be linked to their CPP translocation properties, suggesting that aggregation may aid in translocation across cellular membranes.

Co-incubation of Short Amphiphilic Peptides with Dicer Substrate RNAs Results in β-Sheet Fibrils for Enhanced Gene Silencing in Cancer Cells

RNA can interact with positively charged, amphiphilic peptides to cooperatively assemble into fibrils that enable RNA transport across cancer cellular membranes. RNA decreases the folding energy barrier imposed by the electrostatic repulsion between these charged peptides, thus partaking in RNA-peptide self-assembly along particular pathways in the energy landscape. Specific amphiphilic peptides capable of protecting and transporting RNA across a membrane have Type II' β-turn hairpin forming motifs in their structures, which aids self-assembly into β-sheet fibrils. We employed a set of such cationic, amphiphilic peptides that have random coiled structures in the absence of folding stimuli, to characterize the (peptides):(RNA) assembly. We subjected these complexes to extensive biophysical characterization in vitro and in cell culture. We show that short RNAs (such as Dicer substrate RNAs) can lead these peptides to self-assemble into β-sheet fibrils that have RNA transport capabilities and can act as non-viral delivery vectors for RNA. Modulation in the peptide sequence implicitly alters the way they bind RNA and influence the peptides' ability to transport nucleic acids across membranes.

CLSTN3B promotes lipid droplet maturation and lipid storage in mouse adipocytes

Interorganelle contacts facilitate material exchanges and sustain the structural and functional integrity of organelles. Lipid droplets (LDs) of adipocytes are responsible for energy storage and mobilization responding to body needs. LD biogenesis defects compromise the lipid-storing capacity of adipocytes, resulting in ectopic lipid deposition and metabolic disorders, yet how the uniquely large LDs in adipocytes attain structural and functional maturation is incompletely understood. Here we show that the mammalian adipocyte-specific protein CLSTN3B is crucial for adipocyte LD maturation. CLSTN3B employs an arginine-rich segment to promote extensive contact and hemifusion-like structure formation between the endoplasmic reticulum (ER) and LD, allowing ER-to-LD phospholipid diffusion during LD expansion. CLSTN3B ablation results in reduced LD surface phospholipid density, increased turnover of LD-surface proteins, and impaired LD functions. Our results establish the central role of CLSTN3B in the adipocyte-specific LD maturation pathway that enhances lipid storage and maintenance of metabolic health under caloric overload in mice of both sexes.

A New Gramicidin S Analogue with Potent Antibacterial Activity and Negligible Hemolytic Toxicity

Antibiotic resistance is an urgent threat to global health, with the decreasing efficacy of conventional drugs underscoring the urgency for innovative therapeutic strategies. Antimicrobial peptides present as promising alternatives to conventional antibiotics. Gramicidin S is one such naturally occurring antimicrobial peptide that is effective against Staphylococcus aureus, with a minimum inhibitory concentration (MIC) of 4 μg/mL (3.6 μM). Despite this potent activity, its significant hemolytic toxicity restricts its clinical use to topical applications. Herein, we present rational modifications to the key β-strand and β-turn regions of gramicidin S to concurrently mitigate hemolytic effects, while maintaining potency. Critically, peptide 9 displayed negligible hemolytic toxicity, while possessing significant antibacterial potency against a panel of methicillin-sensitive and methicillin-resistant S. aureus clinical isolates (MIC of 8 μg/mL, 7.2 μM). Given the substantial antibacterial activity and near absence of cytotoxicity, 9 presents as a potential candidate for systemic administration in the treatment of S. aureus bacteremia/sepsis.

Cellular Uptake of Cell-Penetrating Peptides Activated by Amphiphilic p-Sulfonatocalix[4]arenes

We report the synthesis of a series of amphiphilic p-sulfonatocalix[4]arenes with varying alkyl chain lengths (CX4-Cn) and their application as efficient counterion activators for membrane transport of cell-penetrating peptides (CPPs). The enhanced membrane activity is confirmed with the carboxyfluorescein (CF) assay in vesicles and by the direct cytosolic delivery of CPPs into CHO-K1, HCT 116, and KTC-1 cells enabling excellent cellular uptake of the CPPs into two cancer cell lines. Intracellular delivery was confirmed by fluorescence microscopy after CPP entry into live cells mediated by CX4-Cn, which was also quantified after cell lysis by fluorescence spectroscopy. The results present the first systematic exploration of structure-activity relationships for calixarene-based counterion activators and show that CX4-Cn are exceptionally effective in cellular delivery of CPPs. The dodecyl derivative, CX4-C12, serves as best activator. A first mechanistic insight is provided by efficient CPP uptake at 4 °C and in the presence of the endocytosis inhibitor dynasore, which indicates a direct translocation of the CPP-counterion complexes into the cytosol and highlights the potential benefits of CX4-Cn for efficient and direct translocation of CPPs and CPP-conjugated cargo molecules into the cytosol of live cells.

Anion Binding to Ammonium and Guanidinium Hosts: Implications for the Reverse Hofmeister Effects Induced by Lysine and Arginine Residues

Anions have a profound effect on the properties of soluble proteins. Such Hofmeister effects have implications in biologics stability, protein aggregation, amyloidogenesis, and crystallization. However, the interplay between the important noncovalent interactions (NCIs) responsible for Hofmeister effects is poorly understood. To contribute to improving this state of affairs, we report on the NCIs between anions and ammonium and guanidinium hosts 1 and 2, and the consequences of these. Specifically, we investigate the properties of cavitands designed to mimic two prime residues for anion-protein NCIs─lysines and arginines─and the solubility consequences of complex formation. Thus, we report NMR and ITC affinity studies, X-ray analysis, MD simulations, and anion-induced critical precipitation concentrations. Our findings emphasize the multitude of NCIs that guanidiniums can form and how this repertoire qualitatively surpasses that of ammoniums. Additionally, our studies demonstrate the ease by which anions can dispense with a fraction of their hydration-shell waters, rearrange those that remain, and form direct NCIs with the hosts. This raises many questions concerning how solvent shell plasticity varies as a function of anion, how the energetics of this impact the different NCIs between anions and ammoniums/guanidiniums, and how this affects the aggregation of solutes at high anion concentrations.

CLSTN3B enhances adipocyte lipid droplet structure and function via endoplasmic reticulum contact

Interorganelle contacts facilitate material exchanges and sustain the structural and functional integrity of organelles. Lipid droplets (LDs) of adipocytes are responsible for energy storage and mobilization responding to body needs. LD biogenesis defects compromise the lipid-storing capacity of adipocytes, resulting in ectopic lipid deposition and metabolic disorders, yet how the uniquely large LDs in adipocytes attain structural and functional maturation is incompletely understood. Here we show that the mammalian adipocyte-specific protein CLSTN3B is crucial for adipocyte LD maturation. CLSTN3B employs an arginine-rich segment to promote extensive contact and hemifusion-like structure formation between the endoplasmic reticulum (ER) and LD, allowing ER-to-LD phospholipid diffusion during LD expansion. CLSTN3B ablation results in reduced LD surface phospholipid density, increased turnover of LD-surface proteins, and impaired LD functions. Our results establish the central role of CLSTN3B in the adipocyte-specific LD maturation pathway that enhances lipid storage and maintenance of metabolic health under caloric overload.

All-Inorganic Polyoxometalates Act as Superchaotropic Membrane Carriers

Polyoxometalates (POMs) are known antitumoral, antibacterial, antiviral, and anticancer agents and considered as next-generation metallodrugs. Herein, a new biological functionality in neutral physiological media, where selected mixed-metal POMs are sufficiently stable and able to affect membrane transport of impermeable, hydrophilic, and cationic peptides (heptaarginine, heptalysine, protamine, and polyarginine) is reported. The uptake is observed in both, model membranes as well as cells, and attributed to the superchaotropic properties of the polyoxoanions. In view of the structural diversity of POMs these findings pave the way toward their biomedical application in drug delivery or for cell-biological uptake studies with biological effector molecules or staining agents.

Cell-Surface-Retained Peptide Additives for the Cytosolic Delivery of Functional Proteins

The delivery of functional proteins remains a major challenge in advancing biological and pharmaceutical sciences. Herein, we describe a powerful, simple, and highly effective strategy for the intracellular delivery of functional cargoes. Previously, we demonstrated that cell-penetrating peptide (CPP) additives equipped with electrophilic thiol-reactive moieties temporarily attach to the cellular membrane, thereby facilitating the cellular uptake of protein- and antibody-CPP cargoes through direct membrane transduction at low concentrations. Now, we hypothesize that CPP-additives with an increased retention on the cellular membrane will further enhance intracellular uptake. We discovered that adding a small hydrophobic peptide sequence to an arginine-rich electrophilic CPP-additive further improved the uptake of protein-CPP conjugates, whereas larger hydrophobic anchors showed increased cytotoxicity. Cell viability and membrane integrity measurements, structure-activity relationship studies, and quantitative evaluation of protein-CPP uptake revealed important design principles for cell-surface-retained CPP-additives. These investigations allowed us to identify a nontoxic, thiol-reactive CPP-additive containing the hydrophobic ILFF sequence, which can deliver fluorescent model proteins at low micromolar concentrations. This hydrophobic CPP-additive allowed the addition of protein cargoes for intracellular delivery after initial additive incubation. Time-lapse fluorescence microscopy and membrane tension analysis of cells treated with fluorescent ILFF-CPP-additives supported the claim of increased cell surface retention and suggested that the protein-CPP cargoes enter the cell through a mechanism involving lowered cell membrane tension. Finally, we demonstrated that our newly engineered hydrophobic CPP-additive enabled the uptake of a functional macrocyclic peptidic MDM2-inhibitor and a recombinant genome editing protein. This indicates that the developed hydrophobic CPP-additive holds promise as a tool to enhance the intracellular delivery of peptide and protein cargoes.

Why do polyarginines adsorb at neutral phospholipid bilayers and polylysines do not? An insight from density functional theory calculations and molecular dynamics simulations

Adsorption of cell-penetrating peptides (CPPs) at cellular membranes is the first and necessary step for their subsequent translocation across cellular membranes into the cytosol. It has been experimentally shown that CPPs rich in arginine (Arg) amino acid penetrate across phospholipid bilayers more effectively than their lysine (Lys) rich counterparts. In this work, we aim to understand the differences in the first translocation step, adsorption of Arg9 and Lys9 peptides at fully hydrated neutral phosphatidylcholine (PC) and phosphatidylethanolamine (PE) lipid bilayers and evaluate in detail the energetics of the process using molecular dynamics (MD) simulations and free energy calculations of adsorption of the single peptide. We show that the adsorption of Arg9 is energetically feasible, with the free energy of adsorption being ∼-5.0 kcal mol-1 at PC and ∼-5.5 kcal mol-1 at PE bilayers. In contrast, adsorption of Lys9 is not observed at PC bilayers, and their adsorption at PE bilayers is very weak, being ∼-0.5 kcal mol-1. We show by energy decomposition and analysis of peptide hydration along the membrane that significantly stronger electrostatic interactions of Arg9 with lipid phosphate groups, together with the greater loss of peptide hydration (and in turn stronger hydrophobic interactions) along the membrane translocation path, are the main driving factors governing the adsorption of Arg-rich peptides at neutral lipid bilayers in contrast to Lys-rich peptides. Finally, we also compare the energetics in lipid/bilayer systems with the density functional theory (DFT) calculations of the corresponding model systems in the continuum water model and reveal the energetic differences in different environments.

Neurobiochemical characteristics of arginine-rich peptides explain their potential therapeutic efficacy in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer̕ s disease (AD), Parkinson̕ s disease (PD), Huntington̕ s disease (HD), and Amyotrophic Lateral Sclerosis (ALS) require special attention to find new potential treatment methods. This review aims to summarize the current knowledge of the relationship between the biochemical properties of arginine-rich peptides (ARPs) and their neuroprotective effects to deal with the harmful effects of risk factors. It seems that ARPs have portrayed a promising and fantastic landscape for treating neurodegeneration-associated disorders. With multimodal mechanisms of action, ARPs play various unprecedented roles, including as the novel delivery platforms for entering the central nervous system (CNS), the potent antagonists for calcium influx, the invader molecules for targeting mitochondria, and the protein stabilizers. Interestingly, these peptides inhibit the proteolytic enzymes and block protein aggregation to induce pro-survival signaling pathways. ARPs also serve as the scavengers of toxic molecules and the reducers of oxidative stress agents. They also have anti-inflammatory, antimicrobial, and anti-cancer properties. Moreover, by providing an efficient nucleic acid delivery system, ARPs can play an essential role in developing various fields, including gene vaccines, gene therapy, gene editing, and imaging. ARP agents and ARP/cargo therapeutics can be raised as an emergent class of neurotherapeutics for neurodegeneration. Part of the aim of this review is to present recent advances in treating neurodegenerative diseases using ARPs as an emerging and powerful therapeutic tool. The applications and progress of ARPs-based nucleic acid delivery systems have also been discussed to highlight their usefulness as a broad-acting class of drugs.

Adsorption/Desorption of Cationic-Hydrophobic Peptides on Zwitterionic Lipid Bilayer Is Associated with the Possibility of Proton Transfer

Cell-penetrating peptides (CPPs) are short peptides built up from dominantly cationic and hydrophobic amino acid residues with a distinguished ability to pass through the cell membrane. Due to the possibility of linking and delivering the appropriate cargo at the desired location, CPPs are considered an economic and less invasive alternative to antibiotics. Besides knowing that their membrane passage mechanism is a complex function of CPP chemical composition, the ionic strength of the solution, and the membrane composition, all other details on how they penetrate cell membranes are rather vague. The aim of this study is to elucidate the ad(de)sorption of arginine-/lysine- and phenylalanine-rich peptides on a lipid membrane composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipids. DSC and temperature-dependent UV-Vis measurements confirmed the impact of the adsorbed peptides on thermotropic properties of DPPC, but in an inconclusive way. On the other hand, FTIR spectra acquired at 30 °C and 50 °C (when DPPC lipids are found in the gel and fluid phase, respectively) unambiguously confirmed the proton transfer between particular titratable functional groups of R5F2/K5F2 that highly depend on their immediate surroundings (DPPC or a phosphate buffer). Molecular dynamic simulations showed that both peptides may adsorb onto the bilayer, but K5F2 desorbs more easily and favors the solvent, while R5F2 remains attached. The results obtained in this work highlight the importance of proton transfer in the design of CPPs with their desired cargo, as its charge and composition dictates the possibility of entering the cell.

Metallacarborane Cluster Anions of the Cobalt Bisdicarbollide-Type as Chaotropic Carriers for Transmembrane and Intracellular Delivery of Cationic Peptides

Cobalt bisdicarbollides (COSANs) are inorganic boron-based anions that have been previously reported to permeate by themselves through lipid bilayer membranes, a propensity that is related to their superchaotropic character. We now introduce their use as selective and efficient molecular carriers of otherwise impermeable hydrophilic oligopeptides through both artificial and cellular membranes, without causing membrane lysis or poration at low micromolar carrier concentrations. COSANs transport not only arginine-rich but also lysine-rich peptides, whereas low-molecular-weight analytes such as amino acids as well as neutral and anionic cargos (phalloidin and BSA) are not transported. In addition to the unsubstituted isomers (known as ortho- and meta-COSAN), four derivatives bearing organic substituents or halogen atoms have been evaluated, and all six of them surpass established carriers such as pyrenebutyrate in terms of activity. U-tube experiments and black lipid membrane conductance measurements establish that the transport across model membranes is mediated by a molecular carrier mechanism. Transport experiments in living cells showed that a fluorescent peptide cargo, FITC-Arg8, is delivered into the cytosol.

Biodegradable Cationic and Ionizable Cationic Lipids: A Roadmap for Safer Pharmaceutical Excipients

Cationic and ionizable cationic lipids are broadly applied as auxiliary agents, but their use is associated with adverse effects. If these excipients are rapidly degraded to endogenously occurring metabolites such as amino acids and fatty acids, their toxic potential can be minimized. So far, synthesized and evaluated biodegradable cationic and ionizable cationic lipids already showed promising results in terms of functionality and safety. Within this review, an overview about the different types of such biodegradable lipids, the available building blocks, their synthesis and cleavage by endogenous enzymes is provided. Moreover, the relationship between the structure of the lipids and their toxicity is described. Their application in drug delivery systems is critically discussed and placed in context with the lead compounds used in mRNA vaccines. Moreover, their use as preservatives is reviewed, guidance for their design is provided, and an outlook on future developments is given.

Interaction of guanidinium and ammonium cations with phosphatidylcholine and phosphatidylserine lipid bilayers - Calorimetric, spectroscopic and molecular dynamics simulations study

The ability of arginine-rich peptides to cross the lipid bilayer and enter cytoplasm, unlike their lysine-based analogues, is intensively studied in the context of cell-penetrating peptides. Although the experiments have not yet reconstructed their internalization mechanism, the computational studies have shown that the type or charge of lipid polar groups is one of the crucial factors in their translocation. In order to gain more detailed insight into the interaction of guanidinium (Gdm⁺) and ammonium (NH₄⁺) cations, as important building blocks in arginine and lysine amino acids, with lipid bilayers, we conducted the experimental and computational study that tackles this phenomenon. The adsorption of Gdm⁺ and NH₄⁺ on lipid bilayers prepared from a zwitterionic (DPPC) and an anionic (DPPS) lipid was examined by thermoanalytic and spectroscopic techniques. Using temperature-dependent UV-Vis spectroscopy and DSC calorimetry we determined the impact of Gdm⁺ and NH₄⁺ on the thermotropic properties of lipid bilayers. FTIR data, along with molecular dynamics simulations, unraveled the molecular-level details on the nature of their interactions, showing the proton transfer between NH₄⁺ and DPPS, but not between Gdm⁺ and DPPS. The findings originated from this work imply that Gdm⁺ and NH₄⁺ form qualitatively different interactions with lipids of different charge which is reflected in the physico-chemical interactions that arginine-and lysine-based peptides establish at a complex and chemically heterogeneous environment such as the biological membrane.

Lipid-Specific Direct Translocation of the Cell-Penetrating Peptide NAF-144-67 across Bilayer Membranes

The cell-penetrating peptide NAF-1 has recently emerged as a promising candidate for selective penetration and destruction of cancer cells. It displays numerous membrane-selective behaviors including cell-specific uptake and organelle-specific degradation. In this work, we explore membrane penetration and translocation of NAF-1 in model lipid bilayer vesicles as a function of lipid identity in zwitterionic phosphatidylcholine lipids mixed with anionic phosphatidylserine, phosphatidylglycerol, and phosphatidic acid lipids. By monitoring the digestion of NAF-1 using the protease trypsin located inside but not outside the vesicles, we determined that the translocation of NAF-1 was significantly enhanced by the presence of phosphatidic acid in the membrane compared to the other three anionic or zwitterionic lipids. These findings were correlated to fluorescence measurements of dansyl-labeled NAF-1, which revealed whether noncovalent interactions between NAF-1 and the bilayer were most stable either at the membrane/solution interface or within the membrane interior. Phosphatidic acid promoted interactions with fatty acid tails, while phosphatidylcholine, phosphatidylserine, and phosphatidylglycerol stabilized interactions with polar lipid headgroups. Interfacial vibrational sum frequency spectroscopy experiments revealed that the phosphate moiety on phosphatidic acid headgroups was better hydrated than on the other three lipids, which helped to shuttle NAF-1 into the hydrophobic region. Our findings demonstrate that permeation does not depend on the net charge on phospholipid lipid headgroups in these model vesicles and suggest a model wherein NAF-1 crosses membranes selectively due to lipid-specific interactions at bilayer surfaces.

Effect of phosphorylation of protamine-like cationic peptide on the binding affinity to DNA

Protamines are more arginine-rich and more basic than histones and are responsible for providing a highly compacted shape to the sperm heads in the testis. Phosphorylation and dephosphorylation are two events that occur in the late phase of spermatogenesis before the maturation of sperms. In this work, we have studied the effect of phosphorylation of protamine-like cationic peptides using all-atom molecular dynamics simulations. Through thermodynamic analyses, we found that phosphorylation reduces the binding efficiency of such cationic peptides on DNA duplexes. Peptide phosphorylation leads to a less efficient DNA condensation, due to a competition between DNA-peptide and peptide-peptide interactions. We hypothesize that the decrease of peptide bonds between DNA together with peptide self-assembly might allow an optimal re-organization of chromatin and an efficient condensation through subsequent peptide dephosphorylation. Based on the globular and compact conformations of phosphorylated peptides mediated by arginine-phosphoserine H-bonding, we furthermore postulate that phosphorylated protamines could more easily intrude into chromatin and participate to histone release through disruption of histone-histone and histone-DNA binding during spermatogenesis.

Polypharmacological Cell-Penetrating Peptides from Venomous Marine Animals Based on Immunomodulating, Antimicrobial, and Anticancer Properties

Complex pathological diseases, such as cancer, infection, and Alzheimer's, need to be targeted by multipronged curative. Various omics technologies, with a high rate of data generation, demand artificial intelligence to translate these data into druggable targets. In this study, 82 marine venomous animal species were retrieved, and 3505 cryptic cell-penetrating peptides (CPPs) were identified in their toxins. A total of 279 safe peptides were further analyzed for antimicrobial, anticancer, and immunomodulatory characteristics. Protease-resistant CPPs with endosomal-escape ability in Hydrophis hardwickii, nuclear-localizing peptides in Scorpaena plumieri, and mitochondrial-targeting peptides from Synanceia horrida were suitable for compartmental drug delivery. A broad-spectrum S. horrida-derived antimicrobial peptide with a high binding-affinity to bacterial membranes was an antigen-presenting cell (APC) stimulator that primes cytokine release and naïve T-cell maturation simultaneously. While antibiofilm and wound-healing peptides were detected in Synanceia verrucosa, APC epitopes as universal adjuvants for antiviral vaccination were in Pterois volitans and Conus monile. Conus pennaceus-derived anticancer peptides showed antiangiogenic and IL-2-inducing properties with moderate BBB-permeation and were defined to be a tumor-homing peptide (THP) with the ability to inhibit programmed death ligand-1 (PDL-1). Isoforms of RGD-containing peptides with innate antiangiogenic characteristics were in Conus tessulatus for tumor targeting. Inhibitors of neuropilin-1 in C. pennaceus are proposed for imaging probes or therapeutic delivery. A Conus betulinus cryptic peptide, with BBB-permeation, mitochondrial-targeting, and antioxidant capacity, was a stimulator of anti-inflammatory cytokines and non-inducer of proinflammation proposed for Alzheimer's. Conclusively, we have considered the dynamic interaction of cells, their microenvironment, and proportional-orchestrating-host- immune pathways by multi-target-directed CPPs resembling single-molecule polypharmacology. This strategy might fill the therapeutic gap in complex resistant disorders and increase the candidates' clinical-translation chance.

Molecularly Engineered Protein Glues with Superior Adhesion Performance

Naturally inspired proteins are investigated for the development of bioglues that combine adhesion performance and biocompatibility for biomedical applications. However, engineering such adhesives by rational design of the proteins at the molecular level is rarely reported. Herein, it is shown that a new generation of protein-based glues is generated by supramolecular assembly through de novo designed structural proteins in which arginine triggers robust liquid-liquid phase separation. The encoded arginine moieties significantly strengthen multiple molecular interactions in the complex, leading to ultrastrong adhesion on various surfaces, outperforming many chemically reacted and biomimetic glues. Such adhesive materials enable quick visceral hemostasis in 10 s and outstanding tissue regeneration due to their robust adhesion, good biocompatibility, and superior antibacterial capacity. Remarkably, their minimum inhibitory concentrations are orders of magnitude lower than clinical antibiotics. These advances offer insights into molecular engineering of de novo designed protein glues and outline a general strategy to fabricate mechanically strong protein-based materials for surgical applications.

Charge-based drug delivery to cartilage: Hydrophobic and not electrostatic interactions are the dominant cause of competitive binding of cationic carriers in synovial fluid

Charge-based drug delivery has proven to be effective for targeting negatively charged cartilage for the treatment of osteoarthritis. Cartilage is surrounded by synovial fluid (SF), which is comprised of negatively charged hyaluronic acid and hydrophobic proteins that can competitively bind cationic carriers and prevent their transport into cartilage. Here we investigate the relative contributions of charge and hydrophobic effects on the binding of cationic carriers within healthy and arthritic SF by comparing the transport of arginine-rich cartilage targeting cationic peptide carriers with hydrophilic (CPC +14N) or hydrophobic property (CPC +14A). CPC +14N had significantly greater intra-cartilage uptake in presence of SF compared to CPC +14A in-vitro and in vivo. In presence of individual anionic SF constituents, both CPCs maintained similar high intra-cartilage uptake while in presence of hydrophobic constituents, CPC +14N had greater uptake confirming that hydrophobic and not charge interactions are the dominant cause of competitive binding within SF. Results also demonstrate that short-range effects can synergistically stabilize intra-cartilage charge-based binding - a property that can be utilized for enhancing drug-carrier residence time in arthritic cartilage with diminished negative fixed charge density. The work provides a framework for the rational design of cationic carriers for developing targeted therapies for another complex negatively charged environments. STATEMENT OF SIGNIFICANCE: This work demonstrates that hydrophobic and not charge interactions are the dominant cause of the binding of cationic carriers in synovial fluid. Therefore, cationic carriers can be effectively used for cartilage targeting if they are made hydrophilic. This can facilitate clinical translation of various osteoarthritis drugs for cartilage repair that have failed due to a lack of effective cartilage targeting methods. It also demonstrates that short-range hydrogen bonds can synergistically stabilize electrostatic binding in cartilage offering a method for enhancing the targeting and residence time of cationic carriers within arthritic cartilage with reduced charge density. Finally, the cartilage-synovial fluid unit provides an excellent model of a complex negatively charged environment and allows us to generalize these findings and develop targeted therapies for other charged tissue-systems.

Ionic Strength and Solution Composition Dictate the Adsorption of Cell-Penetrating Peptides onto Phosphatidylcholine Membranes

Adsorption of arginine-rich positively charged peptides onto neutral zwitterionic phosphocholine (PC) bilayers is a key step in the translocation of those potent cell-penetrating peptides into the cell interior. In the past, we have shown both theoretically and experimentally that polyarginines adsorb to the neutral PC-supported lipid bilayers in contrast to polylysines. However, comparing our results with previous studies showed that the results often do not match even at the qualitative level. The adsorption of arginine-rich peptides onto 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) may qualitatively depend on the actual experimental conditions where binding experiments have been performed. In this work, we systematically studied the adsorption of R₉ and K₉ peptides onto the POPC bilayer, aided by molecular dynamics (MD) simulations and fluorescence cross-correlation spectroscopy (FCCS) experiments. Using MD simulations, we tested a series of increasing peptide concentrations, in parallel with increasing Na⁺ and Ca²⁺ salt concentrations, showing that the apparent strength of adsorption of R₉ decreases upon the increase of peptide or salt concentration in the system. The key result from the simulations is that the salt concentrations used experimentally can alter the picture of peptide adsorption qualitatively. Using FCCS experiments with fluorescently labeled R₉ and K₉, we first demonstrated that the binding of R₉ to POPC is tighter by almost 2 orders of magnitude compared to that of K₉. Finally, upon the addition of an excess of either Na⁺ or Ca²⁺ ions with R₉, the total fluorescence correlation signal is lost, which implies the unbinding of R₉ from the PC bilayer, in agreement with our predictions from MD simulations.

A nanoparticle probe for the imaging of autophagic flux in live mice via magnetic resonance and near-infrared fluorescence

Autophagy-the lysosomal degradation of cytoplasmic components via their sequestration into double-membraned autophagosomes-has not been detected non-invasively. Here we show that the flux of autophagosomes can be measured via magnetic resonance imaging or serial near-infrared fluorescence imaging of intravenously injected iron oxide nanoparticles decorated with cathepsin-cleavable arginine-rich peptides functionalized with the near-infrared fluorochrome Cy5.5 (the peptides facilitate the uptake of the nanoparticles by early autophagosomes, and are then cleaved by cathepsins in lysosomes). In the heart tissue of live mice, the nanoparticles enabled quantitative measurements of changes in autophagic flux, upregulated genetically, by ischaemia-reperfusion injury or via starvation, or inhibited via the administration of a chemotherapeutic or the antibiotic bafilomycin. In mice receiving doxorubicin, pre-starvation improved cardiac function and overall survival, suggesting that bursts of increased autophagic flux may have cardioprotective effects during chemotherapy. Autophagy-detecting nanoparticle probes may facilitate the further understanding of the roles of autophagy in disease.

Boron clusters as broadband membrane carriers

The membrane translocation of hydrophilic substances constitutes a challenge for their application as therapeutic compounds and labelling probes^1–4. To remedy this, charged amphiphilic molecules have been classically used as carriers^3,5. However, such amphiphilic carriers may cause aggregation and non-specific membrane lysis^6,7. Here we show that globular dodecaborate clusters, and prominently B₁₂Br₁₂²⁻, can function as anionic inorganic membrane carriers for a broad range of hydrophilic cargo molecules (with molecular mass of 146–4,500 Da). We show that cationic and neutral peptides, amino acids, neurotransmitters, vitamins, antibiotics and drugs can be carried across liposomal membranes. Mechanistic transport studies reveal that the carrier activity is related to the superchaotropic nature of these cluster anions^8–12. We demonstrate that B₁₂Br₁₂²⁻ affects cytosolic uptake of different small bioactive molecules, including the antineoplastic monomethyl auristatin F, the proteolysis targeting chimera dBET1 and the phalloidin toxin, which has been successfully delivered in living cells for cytoskeleton labelling. We anticipate the broad and distinct delivery spectrum of our superchaotropic carriers to be the starting point of conceptually distinct cell-biological, neurobiological, physiological and pharmaceutical studies.

The superchaotropic nature of globular boron cluster anions enables direct passage of a wide range of molecules across lipid membranes.

Voltage-Induced Adsorption of Cationic Nanoparticles on Lipid Membranes

We evaluate the effects of an applied electric potential on the adsorption/desorption mechanism of cationic nanoparticles on lipid membranes. By applying a molecular theory that allows calculating nanoparticle adsorption isotherms and free-energy profiles, we identify the conditions under which the external voltage promotes the adsorption of nanoparticles coated with cell penetrating peptides. We consider symmetric and asymmetric membranes made of neutral and acidic lipids and cover a wide range of environmental conditions (external voltage, pH, salt, and nanoparticles concentration) relevant to both electrochemical experiments and biological systems. For neutral membranes at low concentration of salt, a moderate external voltage (<100 mV) induces spontaneous adsorption of nanoparticles. For membranes containing a small fraction of anionic lipids, the external potential has little effect on the interfacial concentration of nanoparticles, and the membrane surface charge dominates the adsorption behavior. In all cases, the membrane-particle effective interactions, and its dependence on the external bias, are strongly modulated by the concentration of salt. At 100 mM NaCl, the external potential has almost no effect on the adsorption free energy profiles. In general, we provide a theoretical framework to evaluate the conditions under which nanoparticles are thermodynamically adsorbed or kinetically restrained to the vicinity of the membrane, and to assess the impact of the nanoparticles on the interfacial electrostatic properties.

Benefit of a Short Chain Peptide as a Targeting Ligand of Nanocarriers for a Brain-Driven Purpose

Treatment of glioma remains a critical challenge worldwide, since the therapeutic effect is greatly hindered by poor transportation across the blood brain barrier (BBB) and low penetration into tumor cells. In this study, a peptide-conjugated nano-delivery system was explored for the purpose of glioma therapy. A peptide-decorated copolymer was used to prepare nanoparticles (NPs) by a solvent evaporation method. The particle size was in the range of 160.9 ± 3.3–173.5 ± 3.6 nm with monodistribution, and the zeta potentials ranged from −18.6 ± 1.2 to +7.9 ± 0.6 mV showing an increasing trend with R9-peptide. An in vitro cocultured BBB model illustrated the internalization of peptide-conjugated NPs in bEnd.3 cells followed by uptake by U87-MG cells indicating both BBB-crossing and glioma-penetrating abilities. IVIS (In Vivo Imaging System) images revealed that T7-conjugated NPs specifically accumulated in the brain more than peptide-free NPs and had less biodistribution in nontarget tissues than T7/R9 dual-peptide conjugated NPs. The benefit of T7-peptide as a targeting ligand for NPs across the BBB with accumulation in the brain was elucidated.

Cellular uptake of large biomolecules enabled by cell-surface-reactive cell-penetrating peptide additives

Enabling the cellular delivery and cytosolic bioavailability of functional proteins constitutes a major challenge for the life sciences. Here we demonstrate that thiol-reactive arginine-rich peptide additives can enhance the cellular uptake of protein-CPP conjugates in a non-endocytic mode, even at low micromolar concentration. We show that such thiol- or HaloTag-reactive additives can result in covalently anchored CPPs on the cell surface, which are highly effective at co-delivering protein cargoes. Taking advantage of the thiol reactivity of our most effective CPP additive, we show that Cys-containing proteins can be readily delivered into the cytosol by simple co-addition of a slight excess of this CPP. Furthermore, we demonstrate the application of our 'CPP-additive technique' in the delivery of functional enzymes, nanobodies and full-length immunoglobulin-G antibodies. This new cellular uptake protocol greatly simplifies both the accessibility and efficiency of protein and antibody delivery, with minimal chemical or genetic engineering.

Physicochemical Features and Peculiarities of Interaction of AMP with the Membrane

Antimicrobial peptides (AMPs) are anti-infectives that have the potential to be used as a novel and untapped class of biotherapeutics. Modes of action of antimicrobial peptides include interaction with the cell envelope (cell wall, outer- and inner-membrane). A comprehensive understanding of the peculiarities of interaction of antimicrobial peptides with the cell envelope is necessary to perform a rational design of new biotherapeutics, against which working out resistance is hard for microbes. In order to enable de novo design with low cost and high throughput, in silico predictive models have to be invoked. To develop an efficient predictive model, a comprehensive understanding of the sequence-to-function relationship is required. This knowledge will allow us to encode amino acid sequences expressively and to adequately choose the accurate AMP classifier. A shared protective layer of microbial cells is the inner, plasmatic membrane. The interaction of AMP with a biological membrane (native and/or artificial) has been comprehensively studied. We provide a review of mechanisms and results of interactions of AMP with the cell membrane, relying on the survey of physicochemical, aggregative, and structural features of AMPs. The potency and mechanism of AMP action are presented in terms of amino acid compositions and distributions of the polar and apolar residues along the chain, that is, in terms of the physicochemical features of peptides such as hydrophobicity, hydrophilicity, and amphiphilicity. The survey of current data highlights topics that should be taken into account to come up with a comprehensive explanation of the mechanisms of action of AMP and to uncover the physicochemical faces of peptides, essential to perform their function. Many different approaches have been used to classify AMPs, including machine learning. The survey of knowledge on sequences, structures, and modes of actions of AMP allows concluding that only possessing comprehensive information on physicochemical features of AMPs enables us to develop accurate classifiers and create effective methods of prediction. Consequently, this knowledge is necessary for the development of design tools for peptide-based antibiotics.

How arginine derivatives alter the stability of lipid membranes: dissecting the roles of side chains, backbone and termini

Arginine (R)-rich peptides constitute the most relevant class of cell-penetrating peptides and other membrane-active peptides that can translocate across the cell membrane or generate defects in lipid bilayers such as water-filled pores. The mode of action of R-rich peptides remains a topic of controversy, mainly because a quantitative and energetic understanding of arginine effects on membrane stability is lacking. Here, we explore the ability of several oligo-arginines R[Formula: see text] and of an arginine side chain mimic R[Formula: see text] to induce pore formation in lipid bilayers employing MD simulations, free-energy calculations, breakthrough force spectroscopy and leakage assays. Our experiments reveal that R[Formula: see text] but not R[Formula: see text] reduces the line tension of a membrane with anionic lipids. While R[Formula: see text] peptides form a layer on top of a partly negatively charged lipid bilayer, R[Formula: see text] leads to its disintegration. Complementary, our simulations show R[Formula: see text] causes membrane thinning and area per lipid increase beside lowering the pore nucleation free energy. Model polyarginine R[Formula: see text] similarly promoted pore formation in simulations, but without overall bilayer destabilization. We conclude that while the guanidine moiety is intrinsically membrane-disruptive, poly-arginines favor pore formation in negatively charged membranes via a different mechanism. Pore formation by R-rich peptides seems to be counteracted by lipids with PC headgroups. We found that long R[Formula: see text] and R[Formula: see text] but not short R[Formula: see text] reduce the free energy of nucleating a pore. In short R[Formula: see text], the substantial effect of the charged termini prevent their membrane activity, rationalizing why only longer [Formula: see text] are membrane-active.

Minireview: Mas-related G protein-coupled receptor X2 activation by therapeutic drugs

Symptoms that resemble allergic reactions, such as pruritus, flushing, and hypotension, are common side effects of therapeutic drugs. In a true allergic reaction, Immunoglobulin E (IgE) antibodies recognize the drug and trigger mediator release from mast cells through cross-linking of IgE receptors. However, many drugs can bypass this pathway and can activate mast cells directly through MRGPRX2, a G protein-coupled receptor that responds to a wide range of small molecules, peptides, and proteins that have little in common except for a net positive charge. This review will provide an overview of MRGPRX2, including its expression pattern, studies of its pharmacology, and its orthologs. It also will review evidence for MRGPRX2 activation by many drugs closely associated with these reactions.

Antimicrobial Peptides and Copper(II) Ions: Novel Therapeutic Opportunities

The emergence of new pathogens and multidrug resistant bacteria is an important public health issue that requires the development of novel classes of antibiotics. Antimicrobial peptides (AMPs) are a promising platform with great potential for the identification of new lead compounds that can combat the aforementioned pathogens due to their broad-spectrum antimicrobial activity and relatively low rate of resistance emergence. AMPs of multicellular organisms made their debut four decades ago thanks to ingenious researchers who asked simple questions about the resistance to bacterial infections of insects. Questions such as "Do fruit flies ever get sick?", combined with pioneering studies, have led to an understanding of AMPs as universal weapons of the immune system. This review focuses on a subclass of AMPs that feature a metal binding motif known as the amino terminal copper and nickel (ATCUN) motif. One of the metal-based strategies of hosts facing a pathogen, it includes wielding the inherent toxicity of copper and deliberately trafficking this metal ion into sites of infection. The sudden increase in the concentration of copper ions in the presence of ATCUN-containing AMPs (ATCUN-AMPs) likely results in a synergistic interaction. Herein, we examine common structural features in ATCUN-AMPs that exist across species, and we highlight unique features that deserve additional attention. We also present the current state of knowledge about the molecular mechanisms behind their antimicrobial activity and the methods available to study this promising class of AMPs.

Brain penetrating peptides and peptide-drug conjugates to overcome the blood-brain barrier and target CNS diseases

Nearly one in six people worldwide suffer from disorders of the central nervous system (CNS). There is an urgent need for effective strategies to improve the success rates in CNS drug discovery and development. The lack of effective technologies for delivering drugs and genes to the brain due to the blood-brain barrier (BBB), a structural barrier that effectively blocks most neurotherapeutic agents from reaching the brain, has posed a formidable hurdle for CNS drug development. Brain-homing and brain-penetrating molecular transport vectors, such as brain permeable peptides or BBB shuttle peptides, have shown promise in overcoming the BBB and ferrying the drug molecules to the brain. The BBB shuttle peptides are discovered by phage display technology or derived from natural neurotropic proteins or certain viruses and harness the receptor-mediated transcytosis molecular machinery for crossing the BBB. Brain permeable peptide-drug conjugates (PDCs), composed of BBB shuttle peptides, linkers, and drug molecules, have emerged as a promising CNS drug delivery system by taking advantage of the endogenous transcytosis mechanism and tricking the brain into allowing these bioactive molecules to pass the BBB. Here, we examine the latest development of brain-penetrating peptide shuttles and brain-permeable PDCs as molecular vectors to deliver small molecule drug payloads across the BBB to reach brain parenchyma. Emerging knowledge of the contribution of the peptides and their specific receptors expressed on the brain endothelial cells, choice of drug payloads, the design of PDCs, brain entry mechanisms, and delivery efficiency to the brain are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

The Thiouronium Group for Ultrastrong Pairing Interactions between Polyelectrolytes

Various charged groups may be used as a repeat unit in polyelectrolytes to provide physical interactions between oppositely charged polymers leading to phase separation. The materials formed thus are termed polyelectrolyte complexes or coacervates (PECs). The strength of pairing between positive, Pol⁺, and negative, Pol^-, repeat units depends on the specific identity of the monomer repeat unit. In this work, the pairing strength of the thiouronium group, a cation closely related to guanidinium, is evaluated using a polythiouronium polyelectrolyte. Polymers containing guanidinium, notably polyarginine, a peptide, are known for their unusual behavior, such as the formation of like-charge ion pairs and hydrogen bonding. It is shown here that some of this behavior is carried over to polythiouroniums, which results in exceptionally strong interactions with polyanions such as polysulfonates and polycarboxylates. The resilience of the polythiouronium/Pol^- interaction was evaluated using the buildup of polyelectrolyte multilayers at various salt concentrations and by breaking up preformed PECs with high concentrations of added salt. The thiouronium group even interacts strongly enough with polymeric zwitterions to enable complexation with this nominally weakly interacting, net-neutral polymer.

Surface charge density and fatty acids enhance the membrane permeation rate of CPP-cargo complexes

The CPP-effect makes reference to the process by which the membrane translocation rate of a cargo is enhanced by chemical functionalization with cell-penetrating peptides (CPPs). In this work we combine a simple kinetic model with free-energy calculations to explore the energetic basis of the CPP-effect. Two polyglicines are selected as model hydrophilic cargoes, and nona-arginine as a prototypical CPP. We assess the cargo carrying efficiency of nona-arginine by comparing the adsorption and insertion energies of the cargoes, the cargo-free CPPs, and the CPP-cargo complexes, into lipid membranes of varying composition. We also analyze the effect of modifying the type and concentration of anionic lipids, and the implication of these factors on the translocation rate of the CPP-cargo complex. Of particular interest is the evaluation of the catalytic role of palmitic acid (palmitate) as a promoter of the CPP-effect. We also analyse the influence of the size of the cargo on the membrane adsorption and insertion energies. Our results show that the efficiency of nona-arginine as a transmembrane carrier of simple hydrophilic molecules is modulated by the size of the cargo, and is strongly enhanced by increasing the concentration of anionic lipids and of ionized fatty acids in the membrane.

PlaToLoCo: the first web meta-server for visualization and annotation of low complexity regions in proteins

Low complexity regions (LCRs) in protein sequences are characterized by a less diverse amino acid composition compared to typically observed sequence diversity. Recent studies have shown that LCRs may co-occur with intrinsically disordered regions, are highly conserved in many organisms, and often play important roles in protein functions and in diseases. In previous decades, several methods have been developed to identify regions with LCRs or amino acid bias, but most of them as stand-alone applications and currently there is no web-based tool which allows users to explore LCRs in protein sequences with additional functional annotations. We aim to fill this gap by providing PlaToLoCo - PLAtform of TOols for LOw COmplexity-a meta-server that integrates and collects the output of five different state-of-the-art tools for discovering LCRs and provides functional annotations such as domain detection, transmembrane segment prediction, and calculation of amino acid frequencies. In addition, the union or intersection of the results of the search on a query sequence can be obtained. By developing the PlaToLoCo meta-server, we provide the community with a fast and easily accessible tool for the analysis of LCRs with additional information included to aid the interpretation of the results. The PlaToLoCo platform is available at: http://platoloco.aei.polsl.pl/.

Effect of Disulfide Cyclization of Ultrashort Cationic Lipopeptides on Antimicrobial Activity and Cytotoxicity

Ultrashort cationic lipopeptides (USCLs) are considered to be a promising class of antimicrobials with high activity against a broad-spectrum of microorganisms. However, the majority of these compounds are characterized by significant toxicity toward human cells, which hinders their potential application. To overcome those limitations, several approaches have been advanced. One of these is disulfide cyclization that has been shown to improve drug-like characteristics of peptides. In this article the effect of disulfide cyclization of the polar head of N-palmitoylated USCLs on in vitro biological activity has been studied. Lipopeptides used in this study consisted of three or four basic amino acids (lysine and arginine) and cystine in a cyclic peptide. In general, disulfide cyclization of the lipopeptides resulted in peptides with reduced cytotoxicity. Disulfide-cyclized USCLs exhibited improved selectivity between Candida sp., Gram-positive strains and normal cells in contrast to their linear counterparts. Interactions between selected USCLs and membranes were studied by molecular dynamics simulations using a coarse-grained force field. Moreover, membrane permeabilization properties and kinetics were examined. Fluorescence and transmission electron microscopy revealed damage to Candida cell membrane and organelles. Concluding, USCLs are strong membrane disruptors and disulfide cyclization of polar head can have a beneficial effect on its in vitro selectivity between Candida sp. and normal human cells.

Altering the Solubility of the Antibiotic Candidate Nisin-A Computational Study

The growing bacterial resistance to available antibiotics makes it necessary to look for new drug candidates. An example is the lanthionine-containing nisin, which has a broad spectrum of antimicrobial activity. While nisin is widely utilized as a food preservative, its poor solubility and low stability at physiological pH hinder its use as an antibiotic. As the solubility of nisin is controlled by the residues of the hinge region, we have performed molecular dynamics simulations of various mutants and studied their effects on nisin's solubility. These simulations are complicated by the presence of two uncommon residues (dehydroalanine and dehydrobutyrine) in the peptide. The primary goal of the present study is to derive rules for designing new mutants that will be more soluble at physiological pH and, therefore, may serve as a basis for the future antibiotic design. Another aim of our study is to evaluate whether existing force fields can model the solubility of these amino acids accurately in order to motivate further developments of force fields to account for solubility information.

Effect of tetracaine on dynamic reorganization of lipid membranes

To understand the intrinsic influence of a drug on lipid membranes is of critical importance in pharmacological science. Herein, we report fluorescence microscopy analysis of the interaction between the local anesthetic tetracaine (TTC) and planar supported lipid bilayers (SLBs), as model membranes. Our results show that TTC increases lipid chain mobility, destabilizes the SLBs and remarkably induces membrane disruption and solubilization. Upon TTC binding, a local curvature change in the bilayer was observed, which led to the subsequent formation of up to 20-μm-long flexible lipid tubules as well as the formation of micron-size holes. Quantitative analysis revealed that membrane solubilization process can be divided into two distinct different stages as a function of TTC concentration. In the first stage (<800 μM), the bilayer disruption profiles fit well to a Langmuir isotherm, while in the second stage (800 μM-25 mM), TTC solubilizes the membrane in a detergent-like manner. Notably, the onset of membrane solubilization occurred below the critical micelle concentration (cmc) of TTC, indicating a local accumulation of the drug in the membrane. Additionally, cholesterol increases the insertion of TTC into the membrane and thus promotes the solubilization effect of TTC on lipid bilayers. These findings may help to elucidate the possible mechanisms of TTC interaction with lipid membranes, the dose dependent toxicity attributed to local anesthetics, as well as provide valuable information for drug development and modification.