Aug 2026· Fish and Shellfish Immunology· Vol 179, pp.
111685
· 0 citations· 73 references
Medicine
TL;DR
It is demonstrated that integrating structural prediction with experimental validation is an effective strategy for identifying fish-derived innate immune peptides as candidates for biomedical applications.
Abstract
Piscidins are cationic α-helical antimicrobial peptides (AMPs) that constitute a key component of the innate immune defense of teleost fish, yet the relationship between their genomic organization, structural properties, and functional specialization remains incompletely understood. In this study, six piscidin peptides from Epinephelus akaara, Seriola dumerili, Thunnus maccoyii, Argyrosomus regius, Dicentrarchus labrax, and Epinephelus coioides were characterized through an integrated sequence-to-function approach combining comparative genomics, structural modeling, physicochemical analysis, and in vitro validation, with the aim of identifying candidates with potential for biomedical and biotechnological applications. All genes studied exhibited the conserved four-exon, three-intron architecture characteristic of teleost piscidins. Structural modeling and circular dichroism confirmed α-helical conformations under membrane-mimetic conditions, despite measurable differences in hydrophobicity, charge distribution, and predicted membrane insertion parameters. Antimicrobial assays revealed distinct functional profiles: Sd_FI25 and Epinecidin_1 displayed broad antibacterial activity against Gram-positive and Gram-negative pathogens, whereas Dl_FI22 showed selective activity with reduced temporal persistence associated with lower peptide stability. Ea_FF25 exhibited comparatively weak antibacterial potency. Antibiofilm activity varied among peptides and did not uniformly parallel planktonic MIC values. Computational predictions further suggested antiviral and antitumoral potential for several sequences, extending their prospective relevance beyond classical antibacterial roles. Conserved genomic architecture and α-helical structure coexist with pronounced functional diversification among teleost piscidins. These findings demonstrate that integrating structural prediction with experimental validation is an effective strategy for identifying fish-derived innate immune peptides as candidates for biomedical applications.
A novel piscidin was identified in largemouth bass that contained an active peptide of 25 aa with an amphipathic helix possessing distinct hydrophobic and positively charged regions, and was significantly up-regulated in spleen from 6 h to 24 h post-lipopolysaccharide (LPS) stimulation.
J. Tian, Liqiang Zhang, Qihuan Zhang et al.· Fishes· 0 citations
Hemocyanin respiratory pigments are recognized as key effectors of invertebrate innate immunity. Here, we further explore the immunological functions of hemocyanin from the freshwater snail Pomacea canaliculata (PcH), focusing on its potential as a source of cryptic antimicrobial peptides (AMPs) and its ability to mediate bacterial agglutination, combining in silico prediction, structural mapping, synthetic peptide assays, and functional immune tests. In silico analysis identified five PcH-derived peptide candidates with physicochemical features commonly associated with AMPs. Synthetic versions of these peptides inhibited the growth of the Gram-positive bacterium Staphylococcus pseudintermedius, and one peptide also exhibited activity against the Gram-negative bacterium Escherichia coli. These peptides exhibited bacteriostatic effects at low-millimolar concentrations with no detectable hemolytic activity against human erythrocytes. Structural mapping into PcH 3D cryo-EM structure indicated that all predicted AMPs are located in solvent-accessible regions, supporting their potential release by proteolytic processing. Additionally, native PcH exhibited dose-dependent agglutination of both Gram-positive and Gram-negative bacteria, consistent with the presence of exposed immunoglobulin-like domains, providing the first evidence in gastropods. Our findings support the view that PcH may be a multitasking immune effector and identify putative hemocyanin-derived AMPs in an Ampullariidae species, as well as evidence of hemocyanin-mediated microbial agglutinating activity in gastropods. Overall, this study highlights snail hemocyanin as a versatile component of molluscan innate immunity with potential as a source of bioactive peptides.
Ignacio Rafael Chiumiento, K. B. Soldati, Tabata R. Brola et al.· Fish and Shellfish Immunolog...· 0 citations
The rapid emergence of antimicrobial resistance necessitates the development of novel antimicrobial agents with improved efficacy and selectivity. In this study, a dermatoxin-like peptide, dermatoxin-PD1, was identified from the skin secretion of Pachymedusa dacnicolor, and its structure–activity relationship was investigated through a rational truncation strategy based on predicted proteolytic cleavage sites. A series of truncated analogues was generated, among which a shortened peptide fragment (T1) retained potent antimicrobial activity, particularly against Gram-negative bacteria, whereas further truncation resulted in a marked loss of function. Structural analysis revealed that both dermatoxin-PD1 and T1 adopted amphipathic α-helical conformations under membrane-mimicking conditions. Functional assays demonstrated that bacterial killing was associated with membrane permeabilisation and depolarisation, with additional evidence supporting interactions with lipopolysaccharide (LPS). Notably, T1 exhibited remarkably reduced haemolytic and cytotoxic effects compared with the parent peptide, resulting in an improved selectivity profile. These findings provide additional insight into the structure–activity relationship of dermatoxin-like peptides and suggest that protease cleavage-guided truncation may represent a useful strategy for developing shorter and safer antimicrobial peptides.
The skin of Rana amurensis serves as an important defense barrier against microbial challenges, yet the molecular basis of its cutaneous immune defense and antimicrobial peptide (AMP) repertoire remains incompletely understood. Here, we established a skin transcriptomic profile of R. amurensis following Aeromonas hydrophila infection and integrated transcriptomic and bioinformatic approaches to characterize transcriptional responses and identify candidate AMPs. A total of 1669 differentially expressed genes (DEGs) were identified between the uninfected and infected groups, including 1091 up-regulated and 578 down-regulated genes. Infection with A. hydrophila induced marked transcriptional changes in innate immune-related genes and pathways, including differential expression of genes associated with the Toll-like receptor (TLR) signaling pathway. Transcriptome-based screening identified 151 candidate AMP sequences. Based on sequence characteristics, evolutionary conservation, and physicochemical properties (length ≤50 amino acids and net charge ranging from +2 to +9), six candidates were selected and three randomly selected candidates were chemically synthesized and exhibited antimicrobial activity against bacterial pathogens, inducing less than 10% hemolysis and maintaining L929 cell viability above 79% at 64 μg/mL. These findings indicate that A. hydrophila infection induces coordinated transcriptional responses involving innate immune-related pathways and diverse candidate AMPs in R. amurensis. This study supports the utility of transcriptome-guided discovery for identifying candidate AMPs in amphibians and provides insights into the molecular basis of skin defense in R. amurensis.
Gram-negative bacteria present a major clinical challenge but also remain an underexplored source of antibacterial natural products. Resistance-guided genome mining of the entomopathogenic symbiont Xenorhabdus identified the rdb biosynthetic gene cluster, which encodes a putative prodrug antibiotic, pre-rhabdobranin. However, the inability to isolate the proposed active metabolite, rhabdobranin, has prevented direct functional evaluation. Here we report a convergent total synthesis of the proposed structure of pre-rhabdobranin B, which revealed a stereochemical misassignment at the N-terminal arginine residue. Synthesis of both rhabdobranin epimers showed that, although they are nearly indistinguishable by standard analytical methods, inversion at this single stereocenter has a pronounced effect on antibacterial activity. Biological evaluation of the revised rhabdobranin structure revealed potent antibacterial activity against Gram-negative pathogens, including WHO critical-priority carbapenem-resistant Klebsiella pneumoniae. Cellular and biochemical profiling implicated inhibition of protein biosynthesis as its principal antibacterial mechanism. We further show that the GNAT-family acetyltransferase RdbK N-acetylates rhabdobranin, attenuating its activity and establishing a secondary self-resistance mechanism. These findings validate resistance-gene-guided discovery in Gram-negative symbionts as a strategy for uncovering cryptic antibiotics and identify rhabdobranin as a promising scaffold for Gram-negative antibiotic development.
Woonkee S. Jo, Zaynoun Attieh, Jan J. Crames et al.· Journal of the American Chem...· 0 citations
The rapid evolution of pesticide resistance in Plutella xylostella has reduced the effectiveness of conventional pest control methods in cruciferous crops. This study investigated the virulence of Serratia marcescens PXG6 against P. xylostella and identified two putative virulence factors, ser (serralysin) and shlB (hemolysin transporter). Whole-genome sequencing revealed a GC content of 59.65%, 4650 predicted genes, multiple secretion systems (types I, V, and VI), and 715 putative virulence-related genes. Bioinformatic analyses predicted type IV pili, serralysin, hemolysin, and flagella as pathogenic determinants. Purified prodigiosin exhibited concentration-dependent insecticidal activity, whereas bacterial proteins alone caused little larval mortality, indicating that full virulence depends on live bacterial cells. Gene knockout mutants Δser and ΔshlB exhibited altered growth, motility, biofilm formation, and stress tolerance. Deletion of shlB significantly reduced hemolytic activity, protein secretion, and virulence against P. xylostella, whereas Δser had minimal impact on larval survival. Overall, PXG6 pathogenicity involves multiple bacterial components, with shlB playing a key role in virulence. These findings improve our understanding of the pathogenic mechanisms of PXG6 and support the development of S. marcescens-based biocontrol strategies against P. xylostella.
Muhammad Rehan Akhtar, Jun Ma, Yan Sun et al.· Environmental Microbiology· 0 citations
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