Molecular dynamics simulation of the membrane binding and disruption mechanisms by antimicrobial scorpion venom-derived peptides

A Critical Review of Short Antimicrobial Peptides from Scorpion Venoms, Their Physicochemical Attributes, and Potential for the Development of New Drugs

Scorpion venoms have proven to be excellent sources of antimicrobial agents. However, although many of them have been functionally characterized, they remain underutilized as pharmacological agents, despite their evident therapeutic potential. In this review, we discuss the physicochemical properties of short scorpion venom antimicrobial peptides (ssAMPs). Being generally short (13-25 aa) and amidated, their proven antimicrobial activity is generally explained by parameters such as their net charge, the hydrophobic moment, or the degree of helicity. However, for a complete understanding of their biological activities, also considering the properties of the target membranes is of great relevance. Here, with an extensive analysis of the physicochemical, structural, and thermodynamic parameters associated with these biomolecules, we propose a theoretical framework for the rational design of new antimicrobial drugs. Through a comparison of these physicochemical properties with the bioactivity of ssAMPs in pathogenic bacteria such as Staphylococcus aureus or Acinetobacter baumannii, it is evident that in addition to the net charge, the hydrophobic moment, electrostatic energy, or intrinsic flexibility are determining parameters to understand their performance. Although the correlation between these parameters is very complex, the consensus of our analysis suggests that there is a delicate balance between them and that modifying one affects the rest. Understanding the contribution of lipid composition to their bioactivities is also underestimated, which suggests that for each peptide, there is a physiological context to consider for the rational design of new drugs.

Lauric arginate ethyl ester: An update on the antimicrobial potential and application in the food systems

Lauric arginate ethyl ester (LAE), a cationic surfactant with low toxicity, displays excellent antimicrobial activity against a broad range of microorganisms. LAE has been approved as generally recognized as safe (GRAS) for widespread application in certain foods at a maximum concentration of 200 ppm. In this context, extensive research has been carried out on the application of LAE in food preservation for improving the microbiological safety and quality characteristics of various food products. This study aims to present a general review of recent research progress on the antimicrobial efficacy of LAE and its application in the food industry. It covers the physicochemical properties, antimicrobial efficacy of LAE, and the underlying mechanism of its action. This review also summarizes the application of LAE in various foods products as well as its influence on the nutritional and sensory properties of such foods. Additionally, the main factors influencing the antimicrobial efficacy of LAE are reviewed in this work, and combination strategies are provided to enhance the antimicrobial potency of LAE. Finally, the concluding remarks and possible recommendations for the future research are also presented in this review. In summary, LAE has the great potential application in the food industry. Overall, the present review intends to improve the application of LAE in food preservation.

Interaction mechanism of three egg protein derived ACE inhibitory tri-peptides and DPPC membrane using FS, FTIR, and DSC studies

Understanding the interaction of food derived angiotensin converting enzyme (ACE) inhibitory peptides and intestinal epithelial cell membrane may help to improve their absorption. This research aimed to study the molecular interaction of ACE inhibitory tri-peptides ADF, FGR, and MIR with DPPC membrane during absorption process. The DPPC liposome was prepared and characterized, then used as a model membrane. The permeability of tri-peptides across the membrane was investigated using Fluorescence spectroscopy. The effect of tri-peptides on the structure and dynamics of DPPC bilayers was determined using Fourier transform infrared spectroscopy. The effect of tri-peptides on the phase transition temperature in the DPPC membrane was also analyzed using Differential scanning calorimetry. The results showed that ACE inhibitory tri-peptides ADF, FGR, and MIR can penetrate into both the membrane-water interface and hydrophobic region of DPPC bilayer, and the tri-peptide FGR have higher permeability across the membrane.

Assessment of New Strategies to Improve the Performance of Antimicrobial Peptides

In this research, we constructed a novel engineered tripeptide modified with lipoic acid (LA-RWR), followed by crosslinking of lipoic acid to form nanoparticles (c-LA-RWR). LA-RWR was also modified with phenethylamine (PEA) on the C-terminus to achieve better antibacterial activities. The as-prepared c-LA-RWR and LA-RWR-PEA were effective against E.coli, S.aureus, C.albicans, and methicillin-resistant Staphylococcus aureus, with minimum inhibitory concentration values ranging from 2 to 16 µg/mL, which greatly improved the performance of LA-RWR. Similar antibacterial activities were demonstrated in anti-biofilm activity; there was no matter on the biofilm that was already established or forming. Moreover, c-LA-RWR/LA-RWR-PEA remarkably induced cytoplasmic membrane depolarization and outer membrane permeabilization, resulting in varying degrees of damage to the bacterial morphology, which were consistent with the results obtained via electron microscopy. Thus, our results show that c-LA-RWR/LA-RWR-PEA exhibited excellent efficacy against a variety of microorganisms with good biosafety, providing new strategies by which to improve the performance of antimicrobial peptides.

Membrane fluidity, composition, and charge affect the activity and selectivity of the AMP ascaphin-8

Ascaphins are cationic antimicrobial peptides that have been shown to have potential in the treatment of infectious diseases caused by multidrug-resistant pathogens (MDR). However, to date, their principal molecular target and mechanism of action are unknown. Results from peptide prediction software and molecular dynamics simulations confirmed that ascaphin-8 is an alpha-helical peptide. For the first time, the peptide was described as membranotrophic using biophysical approaches including calcein liposome leakage, Laurdan general polarization, and dynamic light scattering. Ascaphin-8's activity and selectivity were modulated by rearranging the spatial distribution of lysine (Var-K5), aspartic acid (Var-D4) residues, or substitution of phenylalanine with tyrosine (Var-Y). The parental peptide and its variants presented high affinity toward the bacterial membrane model (≤2 μM), but lost activity in sterol-enriched membranes (mammal and fungal models, with cholesterol and ergosterol, respectively). The peptide-induced pore size was estimated to be >20 nm in the bacterial model, with no difference among peptides. The same pattern was observed in membrane fluidity (general polarization) assays, where all peptides reduced membrane fluidity of the bacterial model but not in the models containing sterols. The peptides also showed high activity toward MDR bacteria. Moreover, peptide sensitivity of the artificial membrane models compared with pathogenic bacterial isolates were in good agreement.

Contrasting patterns of venom regeneration in a centipede (Scolopendra viridis) and a scorpion (Centruroides hentzi)

As biochemical traits with clear fitness consequences, venoms serve a critical ecological role for the animals that produce them. Understanding how venoms are maintained and regenerated after use will, therefore, provide valuable insight into the ecology of venomous animals. Furthermore, most studies on venomous organisms often require removing animals from the wild and waiting extended periods of time between venom extractions. Uncovering the patterns of venom regeneration across different species will likely lead to the development of more efficient venom extraction protocols, reducing both experimental time and the number of animals required. Using reversed-phase high-performance liquid chromatography, we identified asynchronous regeneration of venom protein component abundances in the centipede Scolopendra viridis but found no evidence for asynchronous venom regeneration in the scorpion Centruroides hentzi. We also observed high levels of intraspecific venom variation in C. hentzi, emphasizing the importance of testing for intraspecific venom variation in studies evaluating the synchronicity of venom regeneration. Although the regeneration of relative venom protein component abundances is an asynchronous process in S. viridis, we provide evidence that the presence-absence of major venom components is not an asynchronous process and suggest that studies relying on just the presence/absence of individual proteins (e.g. bioprospecting, drug discovery) could use catch-and-release methods of venom extraction to reduce the number of animals removed from the wild.

Simulations reveal that antimicrobial BP100 induces local membrane thinning, slows lipid dynamics and favors water penetration

MD simulations reveal that BP100 peptide induces local membrane thinning and negative curvature, slows lipid dynamics and increases the water life time in the lipid hydrophobic core and transmembrane water transport in the direction of the peptide.

Computational studies of membrane pore formation induced by Pin2

Understanding, at the molecular level, the effect of AMPs on biological membranes is of crucial importance given the increasing number of multidrug-resistant bacteria. Being part of an ancient type of innate immunity system, AMPs have emerged as a potential solution for which bacteria have not developed resistance. Traditional antibiotics specifically act on biosynthetic pathways, while AMPs may directly destabilize the lipid membrane, but it is unclear how AMPs affect the membrane's stability. We performed multiscale molecular dynamics simulations to investigate the structural features leading to membrane pores formation on zwitterionic and anionic membranes by the antimicrobial peptide (AMP) Pandinin 2 (Pin2). Some experimental reports propose that Pin2 could form barrel-stave pores, while others suggest that it could form toroidal pores. Since there is no conclusive evidence of which type of pore is formed by Pin2 on bilayers, performing molecular dynamics simulations on these systems could shed some light on whether or not or what type of pore Pin2 forms on model membranes. Our results are focused on a detailed description of the pore formation by Pin2 in POPC and POPE:POPG membranes., which strongly suggest that Pin2 forms a toroidal pore and not a barrel-shaped pore; this type of pore also affects the membrane properties. In the process, a phospholipid remodeling in the POPE:POPG membrane takes place. Moreover, the pores formed by Pin2 indicate that they are selective for the chlorine ion. There are no previous ion selectivity reports for other AMPs with similar physicochemical properties, such as melittin and magainin.Communicated by Ramaswamy H. Sarma.

Design, Screening, and Testing of Non-Rational Peptide Libraries with Antimicrobial Activity: In Silico and Experimental Approaches

One of the challenges of modern biotechnology is to find new routes to mitigate the resistance to conventional antibiotics. Antimicrobial peptides (AMPs) are an alternative type of biomolecules, naturally present in a wide variety of organisms, with the capacity to overcome the current microorganism resistance threat. Here, we reviewed our recent efforts to develop a new library of non-rationally produced AMPs that relies on bacterial genome inherent diversity and compared it with rationally designed libraries. Our approach is based on a four-stage workflow process that incorporates the interplay of recent developments in four major emerging technologies: artificial intelligence, molecular dynamics, surface-display in microorganisms, and microfluidics. Implementing this framework is challenging because to obtain reliable results, the in silico algorithms to search for candidate AMPs need to overcome issues of the state-of-the-art approaches that limit the possibilities for multi-space data distribution analyses in extremely large databases. We expect to tackle this challenge by using a recently developed classification algorithm based on deep learning models that rely on convolutional layers and gated recurrent units. This will be complemented by carefully tailored molecular dynamics simulations to elucidate specific interactions with lipid bilayers. Candidate AMPs will be recombinantly-expressed on the surface of microorganisms for further screening via different droplet-based microfluidic-based strategies to identify AMPs with the desired lytic abilities. We believe that the proposed approach opens opportunities for searching and screening bioactive peptides for other applications.

Atomic force microscopy to elucidate how peptides disrupt membranes

Atomic force microscopy is an increasingly attractive tool to study how peptides disrupt membranes. Often performed on reconstituted lipid bilayers, it provides access to time and length scales that allow dynamic investigations with nanometre resolution. Over the last decade, AFM studies have enabled visualisation of membrane disruption mechanisms by antimicrobial or host defence peptides, including peptides that target malignant cells and biofilms. Moreover, the emergence of high-speed modalities of the technique broadens the scope of investigations to antimicrobial kinetics as well as the imaging of peptide action on live cells in real time. This review describes how methodological advances in AFM facilitate new insights into membrane disruption mechanisms.

BmK NSP, a new sodium channel activator from Buthus martensii Karsch, promotes neurite outgrowth in primary cultured spinal cord neurons

Scorpion venom is a rich source of bioactive compounds that affect neuronal excitability by modulating the activities of various channels/receptors. In the current study, guided by a Ca²⁺ mobilization assay, we purified a new neuroactive peptide designated as BmK NSP (Buthus martensii Karsch neurite-stimulating peptide, MW: 7064.30 Da). The primary structure of BmK NSP was determined by Edman degradation. BmK NSP concentration-dependently elevated intracellular Ca²⁺ concentration ([Ca²⁺]_i) with an EC₅₀ value of 4.18 μM in primary cultured spinal cord neurons (SCNs). Depletion of extracellular Ca²⁺ abolished BmK NSP-triggered Ca²⁺ response. Moreover, we demonstrated that BmK NSP-induced Ca²⁺ response was partially suppressed by the inhibitors of L-type Ca²⁺ channels, Na⁺-Ca²⁺ exchangers and NMDA receptors and was abolished by voltage-gated sodium channel (VGSC) blocker, tetrodotoxin. Whole-cell patch clamp recording demonstrated that BmK NSP delayed VGSC inactivation (EC₅₀ = 1.10 μM) in SCNs. BmK NSP enhanced neurite outgrowth in a non-monotonic manner that peaked at ~30 nM in SCNs. BmK NSP-promoted neurite outgrowth was suppressed by the inhibitors of L-type Ca²⁺ channels, NMDA receptors, and VGSCs. Considered together, these data demonstrate that BmK NSP is a new α-scorpion toxin that enhances neurite outgrowth through main routes of Ca²⁺ influx. Modulation of VGSC activity by α-scorpion toxin might represent a novel strategy to regulate the neurogenesis in SCNs.

Increases in Hydrophilicity and Charge on the Polar Face of Alyteserin 1c Helix Change its Selectivity towards Gram-Positive Bacteria

Recently, resistance of pathogens towards conventional antibiotics has increased, representing a threat to public health globally. As part of the fight against this, studies on alternative antibiotics such as antimicrobial peptides have been performed, and it has been shown that their sequence and structure are closely related to their antimicrobial activity. Against this background, we here evaluated the antibacterial activity of two peptides developed by solid-phase synthesis, Alyteserin 1c (WT) and its mutant derivative (ΔM), which shows increased net charge and reduced hydrophobicity. These structural characteristics were modified as a result of amino acid substitutions on the polar face of the WT helix. The minimum inhibitory concentration (MIC) of both peptides was obtained in Gram-positive and Gram-negative bacteria. The results showed that the rational substitutions of the amino acids increased the activity in Gram-positive bacteria, especially against Staphylococcus aureus, for which the MIC was one-third of that for the WT analog. In contrast to the case for Gram-positive bacteria, these substitutions decreased activity against Gram-negative bacteria, especially in Escherichia coli, for which the MIC was eight-fold higher than that exhibited by the WT peptide. To understand this, models of the peptide behavior upon interacting with membranes of E. coli and S. aureus created using molecular dynamics were studied and it was determined that the helical stability of the peptide is indispensable for antimicrobial activity. The hydrogen bonds between the His20 of the peptides and the phospholipids of the membranes should modulate the selectivity associated with structural stability at the carboxy-terminal region of the peptides.

Interaction of SNARE Mimetic Peptides with Lipid bilayers: Effects of Secondary Structure, Bilayer Composition and Lipid Anchoring

The coiled-coil forming peptides 'K' enriched in lysine and 'E' enriched in glutamic acid have been used as a minimal SNARE mimetic system for membrane fusion. Here we describe atomistic molecular dynamics simulations to characterize the interactions of these peptides with lipid bilayers for two different compositions. For neutral phosphatidylcholine (PC)/phosphatidylethanolamine (PE) bilayers the peptides experience a strong repulsive barrier against adsorption, also observed in potential of mean force (PMF) profiles calculated with umbrella sampling. For peptide K, a minimum of -12 k_BT in the PMF provides an upper bound for the binding free energy whereas no stable membrane bound state could be observed for peptide E. In contrast, the electrostatic interactions with negatively charged phosphatidylglycerol (PG) lipids lead to fast adsorption of both peptides at the head-water interface. Experimental data using fluorescently labeled peptides confirm the stronger binding to PG containing bilayers. Lipid anchors have little effect on the peptide-bilayer interactions or peptide structure, when the peptide also binds to the bilayer in the absence of a lipid anchor. For peptide E, which does not bind to the PC bilayer without a lipid anchor, the presence of such an anchor strengthens the electrostatic interactions between the charged side chains and the zwitterionic head-groups and leads to a stabilization of the peptide's helical fold by the membrane.

Minor sequence modifications in temporin B cause drastic changes in antibacterial potency and selectivity by fundamentally altering membrane activity

Antimicrobial peptides (AMPs) are a potential source of new molecules to counter the increase in antimicrobial resistant infections but a better understanding of their properties is required to understand their native function and for effective translation as therapeutics. Details of the mechanism of their interaction with the bacterial plasma membrane are desired since damage or penetration of this structure is considered essential for AMPs activity. Relatively modest modifications to AMPs primary sequence can induce substantial changes in potency and/or spectrum of activity but, hitherto, have not been predicted to substantially alter the mechanism of interaction with the bacterial plasma membrane. Here we use a combination of molecular dynamics simulations, circular dichroism, solid-state NMR and patch clamp to investigate the extent to which temporin B and its analogues can be distinguished both in vitro and in silico on the basis of their interactions with model membranes. Enhancing the hydrophobicity of the N-terminus and cationicity of the C-terminus in temporin B improves its membrane activity and potency against both Gram-negative and Gram-positive bacteria. In contrast, enhancing the cationicity of the N-terminus abrogates its ability to trigger channel conductance and renders it ineffective against Gram-positive bacteria while nevertheless enhancing its potency against Escherichia coli. Our findings suggest even closely related AMPs may target the same bacterium with fundamentally differing mechanisms of action.

Identification of protegrin-1 as a stable and nontoxic scaffold among protegrin family - a computational approach

Achieving both, nontoxicity and stability in antimicrobial peptides (AMP) is a challenge. This study predicts a structurally stable, nontoxic scaffold among the protegrin family, for future therapeutic peptide analogs. Protegrins (PG) are a class of pharmaceutically approved, in demand AMPs, which require further improvement in terms of nontoxicity and stability. Out of five protegrins viz., PG1, PG2, PG3, PG4 and PG5, PG1 has been predicted as best scaffold. Prediction was based upon sequential elimination of other protegrins, using computational methods to assess the extracellular bacterial membrane penetrability, nontoxicity and structural stability by geometric observables. Initially, PG2 and PG4 showing the lowest membrane penetrability and highest toxicity respectively, were screened out. Among the remaining three protegrins, PG1 displayed both lowest root mean square deviation and radius of gyration, with a considerable occupancy of seven H-bonds and established uniform secondary structure profile throughout its ensembles. Therefore, the authors claim the superiority of PG1 as a nontoxic stable scaffold among its family. Communicated by Ramaswamy H. Sarma.

Antimicrobial cell penetrating peptides with bacterial cell specificity: pharmacophore modelling, quantitative structure activity relationship and molecular dynamics simulation

Current research has shown cell-penetrating peptides and antimicrobial peptides (AMPs) as probable vectors for use in drug delivery and as novel antibiotics. It has been reported that the higher the therapeutic index (TI) the higher would be the bacterial cell penetrating ability. To the best of our knowledge, no in-silico study has been performed to determine bacterial cell specificity of the antimicrobial cell penetrating peptides (aCPP's) based on their TI. The aim of this study was to develop a quantitative structure activity relationship (QSAR) model, which can estimate antimicrobial potential and cell-penetrating ability of aCPPs against S. aureus, to confirm the relationship between the TI and aCPPs and to identify specific descriptors responsible for aCPPs penetrating ability. Molecular dynamics (MD) simulation was also performed to confirm the membrane insertion of the most active aCPPs obtained from the QSAR study. The most appropriate pharmacophore was identified to predict the aCPP's activity. The statistical results confirmed the validity of the model. The QSAR model was successful in identifying the optimal aCPP with high activity prediction and provided insights into the structural requirements to correlate their TI to cell penetrating ability. MD simulation of the best aCPP with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer confirmed its interaction with the membrane and the C-terminal residues of the aCPP played a key role in membrane penetration. The strategy of combining QSAR and molecular dynamics, allowed for optimal estimation of ligand-target interaction and confirmed the importance of Trp and Lys in interacting with the POPC bilayer. Communicated by Ramaswamy H. Sarma.

Analogs of the Scorpion Venom Peptide Stigmurin: Structural Assessment, Toxicity, and Increased Antimicrobial Activity

Scorpion venom is a rich source of biologically active components and various peptides with high-potential therapeutic use that have been characterized for their antimicrobial and antiproliferative activities. Stigmurin is a peptide identified from the Tityus stigmurus venom gland with high antibacterial and antiproliferative activities and low toxicity. Amino acid substitutions in peptides without a disulfide bridge sequence have been made with the aim of reducing their toxicity and increasing their biological activities. The purpose of this study was to evaluate the structural conformation and structural stability, as well as antimicrobial, antiproliferative, and hemolytic activities of two peptide analogs to Stigmurin, denominated StigA6 and StigA16. In silico analysis revealed the α-helix structure for both analog peptides, which was confirmed by circular dichroism. Data showed that the net charge and hydrophobic moment of the analog peptides were higher than those for Stigmurin, which can explain the increase in antimicrobial activity presented by them. Both analog peptides exhibited activity on cancerous cells similar to the native peptide; however, they were less toxic when tested on the normal cell line. These results reveal a potential biotechnological application of the analog peptides StigA6 and StigA16 as prototypes to new therapeutic agents.