Interaction of Halictine-Related Antimicrobial Peptides with Membrane Models

Study on antimicrobial activity of sturgeon skin mucus polypeptides (Rational Design, Self-Assembly and Application)

Despite the favorable biocompatibility of natural antimicrobial peptides (AMPs), their scarcity limits their practical application. Through rational design, the activity of AMPs can be enhanced to expand their application. In this study, we selected a natural sturgeon epidermal mucus peptide, AP-16 (APATPAAPALLPLWLL), as the model molecule and studied its conformational regulation and antimicrobial activity through amino acid substitutions and N-terminal lipidation. The structural and morphological transitions of the peptide self-assemblies were investigated using circular dichroism and transmission electron microscopy. Following amino acid substitution, the conformation of AL-16 (AKATKAAKALLKLWLL) did not change. Following N-terminal alkylation, the C8-AL-16 and C12-AL-16 conformations changed from random coil to β-sheet or α-helix, and the self-assembly changed from nanofibers to nanospheres. AL-16, C8-AL-16, and C8-AL-16 presented significant antimicrobial activity against Pseudomonas and Shewanella at low concentrations. N-terminal alkylation effectively extended the shelf life of Litopenaeus vannamei. These results support the application of natural AMPs.

NGIWY-Amide: A Bioinspired Ultrashort Self-Assembled Peptide Gelator for Local Drug Delivery Applications

Fibrillar structures derived from plant or animal origin have long been a source of inspiration for the design of new biomaterials. The Asn-Gly-Ile-Trp-Tyr-NH2 (NGIWY-amide) pentapeptide, isolated from the sea cucumber Apostichopus japonicus, which spontaneously self-assembles in water to form hydrogel, pertains to this category. In this study, we evaluated this ultra-short cosmetic bioinspired peptide as vector for local drug delivery applications. Combining nuclear magnetic resonance, circular dichroism, infrared spectroscopy, X-ray diffraction, and rheological studies, the synthesized pentapeptide formed a stiff hydrogel with a high β-sheet content. Molecular dynamic simulations aligned well with scanning electron and atomic-force microscopy studies, revealing a highly filamentous structure with the fibers adopting a helical-twisted morphology. Model dye localization within the supramolecular hydrogel provided insights on the preferential distribution of hydrophobic and hydrophilic compounds in the hydrogel network. That was further depicted in the diffusion kinetics of drugs differing in their aqueous solubility and molecular weight, namely, doxorubicin hydrochloride, curcumin, and octreotide acetate, highlighting its versatility as a delivery vector of both hydrophobic and hydrophilic compounds of different molecular weight. Along with the observed cytocompatibility of the hydrogel, the NGIWY-amide pentapeptide may offer new approaches for cell growth, drug delivery, and 3D bioprinting tissue-engineering applications.

Defensing role of novel piscidins from largemouth bass (Micropterus salmoides) with evidence of bactericidal activities and inducible expressional delineation

Micropterus salmoides is an economical important species of freshwater-cultured fish, the in-depth knowledge of its immune system is in urgent development to cope with serious infectious diseases. Piscidin is an important antimicrobial peptide (AMP) family existing in almost all teleosts. However, no piscidin has been reported in largemouth bass. In this study, three novel piscidins (MSPiscidin-1, -2, and -3) were firstly identified and characterized from the largemouth bass. The predicted mature peptides of MSPiscidin-1, -2, and -3 (consists of 24, 27, 25 amino acid residues, respectively) all adopted an amphipathic α-helical conformation representative of cationic AMPs that are important for membrane permeabilization and antibacterial activity. MSPiscidin-2 and -3 indeed displayed strong, broad-spectrum, and highly efficient antimicrobial activities in vitro against aquatic pathogens, but MSPiscidin-1 didn't show direct antimicrobial activity. MSPiscidin-2 and -3 killed bacteria mainly by inducing membrane permeabilization, in addition, they also can interact with bacterial genomic DNA, which might influence the DNA replication and transcription. Besides, MSPiscidin-2 and -3 could effectively inhibit the formation of the bacterial biofilm and eliminate the preformed biofilms. In vivo, MSPiscidin-1-3 genes showed an inducible expression pattern in the tested tissues upon Vibrio harveyi infection, which further indicated the key roles of piscidins in innate immunity in largemouth bass. Overall, this study will supplement the understanding of M. salmoides innate immune system and provide candidates for the design of novel peptide antibacterial agents used in aquaculture.

Polarimetric Measurements of Surface Chirality Based on Linear and Nonlinear Light Scattering

A molecule, molecular aggregate, or protein that cannot be superimposed on its mirror image presents chirality. Most living systems are organized by chiral building blocks, such as amino acids, peptides, and carbohydrates, and any change in their molecular structure (i.e., handedness or helicity) alters the biochemical and pharmacological functions of the molecules, many of which take place at surfaces. Therefore, studying surface chirogenesis at the nanoscale is fundamentally important and derives various applications. For example, since proteins contain highly ordered secondary structures, the intrinsic chirality can be served as a signature to measure the dynamics of protein adsorption and protein conformational changes at biological surfaces. Furthermore, a better understanding of chiral recognition and separation at bio-nanointerfaces is helpful to standardize chiral drugs and monitor the synthesis of adsorbents with high precision. Thus, exploring the changes in surface chirality with polarized excitations would provide structural and biochemical information of the adsorbed molecules, which has led to the development of label-free and noninvasive measurement tools based on linear and nonlinear optical effects. In this review, the principles and selected applications of linear and nonlinear optical methods for quantifying surface chirality are introduced and compared, aiming to conceptualize new ideas to address critical issues in surface biochemistry.

Antibacterial mechanism of brevilaterin B: an amphiphilic lipopeptide targeting the membrane of Listeria monocytogenes

Antimicrobial peptides (AMPs) are recognized as promising safe alternatives to antibiotics for its low drug-resistance. Brevilaterin B, a newly discovered antimicrobial lipopeptide produced by Brevibacillus laterosporus S62-9, exhibits efficient antibacterial activity on Listeria monocytogenes with a minimum inhibitory concentration of 1 μg mL^-1. The present research aimed to investigate the antibacterial mechanism of brevilaterin B against Listeria monocytogenes. Brevilaterin B caused membrane depolarization and the breakup of the cytomembrane as measured by 3,3-dipropylthiadicarbocyanine iodide and transmission electron microscopy, respectively. Using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (7:3) as a model membrane, results proved that brevilaterin B could bind to liposomes, integrate into the lipid bilayer, and consequently increase the permeability of liposomes to calcein. The secondary structure of brevilaterin B also changed from an unstructured coil to a mainly β-sheet conformation as measured by circular dichroism. Brevilaterin B exhibits antibacterial activity by a membrane interaction mechanism, which provides a theoretical basis for using brevilaterin B as a promising natural and effective antimicrobial agent against pathogenic bacteria. KEY POINTS: • Brevilaterin B exhibited antibacterial activity against Listeria monocytogenes. • Brevilaterin B exhibited membrane interaction mechanism. • Brevilaterin B showed conformational change when interacted with liposome.

Halictine-2 antimicrobial peptide shows promising anti-parasitic activity against Leishmania spp

The protozoan parasite Leishmania spp. causes leishmaniases, a group of diseases creating serious health problems in many parts of the world with significant resistance to existing drugs. Insect derived antimicrobial peptides are promising alternatives to conventional drugs against several human disease-causing pathogens because they do not generate resistance. Halictine-2, a novel antimicrobial peptide from the venom of eusocial honeybee, Halictus sexcinctus showed significant anti-leishmanial activity in vitro, towards two life forms of the dimorphic parasite, the free-swimming infective metacyclic promastigotes and the intracellular amastigotes responsible for the systemic infection. The anti-leishmanial activity of the native peptide (P^5S) was significantly enhanced by serine to threonine substitution at position 5 (P^5T). The peptide showed a propensity to form α-helices after substitution at position-5, conferring amphipathicity. Distinct pores observed on the promastigote membrane after P^5T exposure suggested a mechanism of disruption of cellular integrity. Biochemical alterations in the promastigotes after P^5T exposure included generation of increased oxygen radicals with mitochondrial Ca²⁺ release, loss of mitochondrial membrane potential, reduction in total ATP content and increased mitochondrial mass, resulting in quick bioenergetic and chemiosmotic collapse leading to cell death characterized by DNA fragmentation. P^5T was able to reduce intracellular amastigote burden in an in vitro model of Leishmania infection but did not alter the proinflammatory cytokines like TNF-α and IL-6. The ability of the P^5T peptide to kill the Leishmania parasite with negligible haemolytic activity towards mouse macrophages and human erythrocytes respectively, demonstrates its potential to be considered as a future antileishmanial drug candidate.

Chiroptical Properties and Conformation of Four Lasiocepsin-Related Antimicrobial Peptides: Structural Role of Disulfide Bridges

We report an investigation of the role of disulfide bridges in the 27-residue antimicrobial peptide lasiocepsin (I) containing two disulfide groups (Cys8–Cys25, Cys17–Cys27) and three its analogs lacking one (II, III) or both (IV) native disulfides. Selective alternate incorporation of one or both disulfide bridges influences symmetry, conformation and biological properties of these peptides as demonstrated in their chiroptical (particularly Raman) properties. The effect of modifying the disulfide bridge pattern on the peptide secondary structure is investigated in water and in the presence of 2,2,2-trifluoroethanol and sodium dodecyl sulphate. A combination of experimental electronic and vibrational chiroptical data shows that both disulfide groups are necessary for stabilizing lasiocepsin secondary structure. While the Cys8–Cys25 disulfide group is important for sustaining lasiocepsin tertiary structure and maintaining its biological activity, the Cys17–Cys27 disulfide bridge has a supporting function consisting in reducing peptide flexibility.

Self-Association of Antimicrobial Peptides: A Molecular Dynamics Simulation Study on Bombinin

Antimicrobial peptides (AMPs) are a diverse group of membrane-active peptides which play a crucial role as mediators of the primary host defense against microbial invasion. Many AMPs are found to be fully or partially disordered in solution and to acquire secondary structure upon interaction with a lipid membrane. Here, we report molecular dynamics simulations studies on the solution behaviour of a specific AMP, bombinin H2. We show that in monomeric form in water solution the peptide is somewhat disordered and preferably adopts a helix-loop-helix conformation. However, when more than a single monomer is placed in the solution, the peptides self-associate in aggregates. Within the aggregate, the peptides provide each other with an amphipathic environment that mimics the water–membrane interface, which allows them to adopt a single-helix structure. We hypothesise that this is the mechanism by which bombinin H2 and, possibly, other small linear AMPs reach the target membrane in a functional folded state and are able to effectively exert their antimicrobial action on it.