Histidine-Mediated Ion Specific Effects Enable Salt Tolerance of a Pore-Forming Marine Antimicrobial Peptide

A novel antimicrobial peptide Larimicin78-102 from large yellow croaker (Larimichthys crocea) shows potent antibacterial activity in vitro and enhances resistance to vibrio fluvialis infection in vivo

Antimicrobial peptides (AMPs) are considered a key component of innate immunity, playing a vital role in host defense. In the study, a novel functional gene, named Larimicin, was identified from large yellow croaker Larimichthys crocea. The Larimicin gene was widely distributed in multiple tissues of healthy L. crocea and was significantly induced in the liver after Vibrio alginolyticus or Vibrio parahaemolyticus infection. Larimicin78-102, a truncated peptide derived from Larimicin, showed broad-spectrum antimicrobial activity and a binding affinity with LPS. It exhibited effective bactericidal activity against the common aquatic pathogens Vibrio fluvialis, Pseudomonas fluorescens, and Pseudomonas putida. It also showed anti-biofilm activity against three aquatic pathogens. Moreover, Larimicin78-102 disrupted the integrity of the outer and inner membranes, resulting in ATP leakage and intracellular ROS accumulation, which ultimately led to bacterial cell death. Larimicin78-102 exhibited good thermal stability and cation tolerance, with no obvious cytotoxicity or hemolytic activity. Notably, Larimicin78-102 significantly improved the survival rate of L. crocea infected with V. fluvialis, raising it to 95 %, indicating its anti-infective role in vivo. In addition, Larimicin78-102 significantly reduced the expression of the pro-inflammatory cytokines TNF-α and IL-1β, while up-regulating the anti-inflammatory factor IL-4 mRNA level. It also elevated the expression levels of piscidin, hepcidin, and lysozyme, as well as enhanced the enzymatic activity of lysozyme. Taken together, Larimicin78-102 is a potential antibacterial agent for use in aquaculture to combat V. fluvialis infection diseases in the future.

An effective approach to obtain functional poly-β-peptides for combating drug-resistant bacterial infections

The high mortality of drug-resistant bacterial infections, especially those caused by multidrug-resistant Gram-negative pathogens, highlights an urgent demand for promising antimicrobial strategies. Host defense peptide (HDP)-mimicking poly-β-peptides have demonstrated significant potential in combating drug-resistant bacterial infections, with their antimicrobial activity closely dependent on their side-chain structures. However, the restricted structural diversity of poly-β-peptides necessitates efficient synthetic methods to expand their diversity, particularly positively charged side-chain structures. This study presents a water-tolerant approach that facilitates the controllable synthesis of poly-β-peptides with different chain lengths and structurally diverse side chains, including primary amines, tertiary amines, as well as alkyl, aryl, and methoxy groups. This approach serves as an HDP-mimicking discovery platform to obtain the optimal poly-β-peptide, AOc0.8HNL0.2, which exhibits broad-spectrum antibacterial activity and high selectivity against drug-resistant bacteria. The antibacterial mechanism studies reveal that AOc0.8HNL0.2 disrupts the membrane of Gram-negative bacteria. In vivo evaluations substantiate the therapeutic potential of AOc0.8HNL0.2 in treating drug-resistant bacterial infections with no observable toxicity. This study underscores the potential of this convenient synthetic strategy as a promising platform for developing antimicrobial poly-β-peptides to combat the growing threat of drug-resistant bacterial infections.

A dual-targeting antifungal is effective against multidrug-resistant human fungal pathogens

Drug-resistant fungal infections pose a significant threat to human health. Dual-targeting compounds, which have multiple targets on a single pathogen, offer an effective approach to combat drug-resistant pathogens, although ensuring potent activity and high selectivity remains a challenge. Here we propose a dual-targeting strategy for designing antifungal compounds. We incorporate DNA-binding naphthalene groups as the hydrophobic moieties into the host defence peptide-mimicking poly(2-oxazoline)s. This resulted in a compound, (Gly0.8Nap0.2)20, which targets both the fungal membrane and DNA. This compound kills clinical strains of multidrug-resistant fungi including Candida spp., Cryptococcus neoformans, Cryptococcus gattii and Aspergillus fumigatus. (Gly0.8Nap0.2)20 shows superior performance compared with amphotericin B by showing not only potent antifungal activities but also high antifungal selectivity. The compound also does not induce antimicrobial resistance. Moreover, (Gly0.8Nap0.2)20 exhibits promising in vivo therapeutic activities against drug-resistant Candida albicans in mouse models of skin abrasion, corneal infection and systemic infection. This study shows that dual-targeting antifungal compounds may be effective in combating drug-resistant fungal pathogens and mitigating fungal resistance.

Antimicrobial peptides as promising antibiotic adjuvants to combat drug-resistant pathogens

The widespread antimicrobial resistance (AMR) calls for the development of new antimicrobial strategies. Antibiotic adjuvant rescues antibiotic activity and increases the life span of the antibiotics, representing a more productive, timely, and cost-effective strategy in fighting drug-resistant pathogens. Antimicrobial peptides (AMPs) from synthetic and natural sources are considered new-generation antibacterial agents. Besides their direct antimicrobial activity, growing evidence shows that some AMPs effectively enhance the activity of conventional antibiotics. The combinations of AMPs and antibiotics display an improved therapeutic effect on antibiotic-resistant bacterial infections and minimize the emergence of resistance. In this review, we discuss the value of AMPs in the age of resistance, including modes of action, limiting evolutionary resistance, and their designing strategies. We summarise the recent advances in combining AMPs and antibiotics against antibiotic-resistant pathogens, as well as their synergistic mechanisms. Lastly, we highlight the challenges and opportunities associated with the use of AMPs as potential antibiotic adjuvants. This will shed new light on the deployment of synergistic combinations to address the AMR crisis.

Self-Assembled DNA Machine and Selective Complexation Recognition Enable Rapid Homogeneous Portable Quantification of Lung Cancer CTCs

In this study, we systematically investigated the interactions between Cu2+ and various biomolecules, including double-stranded DNA, Y-shaped DNA nanospheres, the double strand of the hybridization chain reaction (HCR), the network structure of cross-linked HCR (cHCR), and small molecules (PPi and His), using Cu2+ as an illustrative example. Our research demonstrated that the coordination between Cu2+ and these biomolecules not only is suitable for modulating luminescent material signals through complexation reactions with Cu2+ but also enhances signal intensities in materials based on chemical reactions by increasing spatial site resistance and local concentration. Building upon these findings, we harnessed the potential for signal amplification in self-assembled DNA nanospheres and the selective complexation modulation of calcein in conjunction with the aptamer targeting mucin 1 as a recognition probe. We applied this approach to the analysis of circulating tumor cells, with the lung cancer cell line A549 serving as a representative model. Our assay, utilizing both a fluorometer and a handheld detector, achieved impressive detection limits of ag/ml and single-cell levels for mucin 1 and A549 cells, and this approach was successfully validated using 46 clinical samples, yielding 100% specificity and 86.5% sensitivity. Consequently, our strategy has paved the way for more portable and precise disease diagnosis.

"AMP plus": Immunostimulant-Inspired Design Based on Chemotactic Motif-(PhHAhPH)n

Ability to stimulate antimicrobial immunity has proven to be a useful therapeutic strategy in treating infections, especially in the face of increasing antibiotic resistance. Natural antimicrobial peptides (AMPs) exhibiting immunomodulatory functions normally encompass complex activities, which make it difficult to optimize their therapeutic benefits. Here, a chemotactic motif was harnessed as a template to design a series of AMPs with immunostimulatory activities plus bacteria-killing activities ("AMP plus"). An amphipathic peptide ((PhHAhPH)n) was employed to improve the antimicrobial impact and expand the therapeutic potential of the chemotactic motif that lacked obvious bacteria-killing properties. A total of 18 peptides were designed and evaluated for their structure-activity relationships. Among the designed, KWH2 (1) potently killed bacteria and exhibited a narrow antimicrobial spectrum against Gram-negative bacteria and (2) activated macrophages (i.e., inducing Ca2+ influx, cell migration, and reactive oxygen species production) as a macrophage chemoattractant. Membrane permeabilization is the major antimicrobial mechanism of KWH2. Furthermore, the mouse subcutaneous abscess model supported the dual immunomodulatory and antimicrobial potential of KWH2 in vivo. The above results confirmed the efficiency of KWH2 in treating bacterial infection and provided a viable approach to develop immunomodulatory antimicrobial materials with desired properties.

Regulation of salt tolerance in the roots of Zea mays by L-histidine through transcriptome analysis

Soil salinization is an important worldwide environmental problem and the main reason to reduce agricultural productivity. Recent findings suggested that histidine is a crucial residue that influences the ROS reduction and improves the plants' tolerance to salt stress. Herein, we conducted experiments to understand the underlying regulatory effects of histidine on maize root system under salt stress (100 mM NaCl solution system). Several antioxidant enzymes were determined. The related expressed genes (DEGs) with its pathways were observed by Transcriptome technologies. The results of the present study confirmed that histidine can ameliorate the adverse effects of salt stress on maize root growth. When the maize roots exposed to 100 mM NaCl were treated with histidine, the accumulation of superoxide anion radicals, hydrogen peroxide, and malondialdehyde, and the content of nitrate nitrogen and ammonium nitrogen were significantly reduced; while the activities of superoxide dismutase, peroxidase, catalase, nitrate reductase, glutamine synthetase, and glutamate synthase were significantly increased. Transcriptome analysis revealed that a total of 454 (65 up-regulated and 389 down-regulated) and 348 (293 up-regulated and 55 down-regulated) DEGs were observed when the roots under salt stress were treated with histidine for 12 h and 24 h, respectively. The pathways analysis of those DEGs showed that a small number of down-regulated genes were enriched in phytohormone signaling and phenylpropanoid biosynthesis at 12 h after histidine treatment, and the DEGs involved in the phytohormone signaling, glycolysis, and nitrogen metabolism were significantly enriched at 24 h after treatment. These results of gene expression and enzyme activities suggested that histidine can improve the salt tolerance of maize roots by enriching some DEGs involved in plant hormone signal transduction, glycolysis, and nitrogen metabolism pathways.

A Novel Antimicrobial Peptide Spampcin56-86 from Scylla paramamosain Exerting Rapid Bactericidal and Anti-Biofilm Activity In Vitro and Anti-Infection In Vivo

The abuse of antibiotics leads to the increase of bacterial resistance, which seriously threatens human health. Therefore, there is an urgent need to find effective alternatives to antibiotics, and antimicrobial peptides (AMPs) are the most promising antibacterial agents and have received extensive attention. In this study, a novel potential AMP was identified from the marine invertebrate Scylla paramamosain and named Spampcin. After bioinformatics analysis and AMP database prediction, four truncated peptides (Spa31, Spa22, Spa20 and Spa14) derived from Spampcin were screened, all of which showed potent antimicrobial activity with different antibacterial spectrum. Among them, Spampcin_56-86 (Spa31 for short) exhibited strong bactericidal activity against a variety of clinical pathogens and could rapidly kill the tested bacteria within minutes. Further analysis of the antibacterial mechanism revealed that Spa31 disrupted the integrity of the bacterial membrane (as confirmed by scanning electron microscopy observation, NPN, and PI staining assays), leading to bacterial rupture, leakage of cellular contents (such as elevated extracellular ATP), increased ROS production, and ultimately cell death. Furthermore, Spa31 was found to interact with LPS and effectively inhibit bacterial biofilms. The antibacterial activity of Spa31 had good thermal stability, certain ion tolerance, and no obvious cytotoxicity. It is worth noting that Spa31 could significantly improve the survival rate of zebrafish Danio rerio infected with Pseudomonas aeruginosa, indicating that Spa31 played an important role in anti-infection in vivo. This study will enrich the database of marine animal AMPs and provide theoretical reference and scientific basis for the application of marine AMPs in medical fields.

Free-energy landscapes and insertion pathways for peptides in membrane environment

Free-energy landscapes for short peptides-specifically for variants of the pH low insertion peptide (pHLIP)-in the heterogeneous environment of a lipid bilayer or cell membrane are constructed, taking into account a set of dominant interactions and the conformational preferences of the peptide backbone. Our methodology interprets broken internal H-bonds along the backbone of a polypeptide as statistically interacting quasiparticles, activated from the helix reference state. The favored conformation depends on the local environment (ranging from polar to nonpolar), specifically on the availability of external H-bonds (with H_{2}O molecules or lipid headgroups) to replace internal H-bonds. The dominant side-chain contribution is accounted for by residue-specific transfer free energies between polar and nonpolar environments. The free-energy landscape is sensitive to the level of pH in the aqueous environment surrounding the membrane. For high pH, we identify pathways of descending free energy that suggest a coexistence of membrane-adsorbed peptides with peptides in solution. A drop in pH raises the degree of protonation of negatively charged residues and thus increases the hydrophobicity of peptide segments near the C terminus. For low pH, we identify insertion pathways between the membrane-adsorbed state and a stable trans-membrane state with the C terminus having crossed the membrane.