Functional characterization of two defensin isoforms of the hard tick Ixodes ricinus

<p>Abstract</p> <p>Background</p> <p>The immune system of ticks is stimulated to produce many pharmacologically active molecules during feeding and especially during pathogen invasion. The family of cationic peptides - defensins - represents a specific group of antimicrobial compounds with six conserved cysteine residues in a molecule.</p> <p>Results</p> <p>Two isoforms of the defensin gene <it>(def1 </it>and <it>def2</it>) were identified in the European tick <it>Ixodes ricinus</it>. Expression of both genes was induced in different tick organs by a blood feeding or pathogen injection. We have tested the ability of synthetic peptides def1 and def2 to inhibit the growth or directly kill several pathogens. The antimicrobial activities (expressed as minimal inhibition concentration and minimal bactericidal concentration values) against Gram positive bacteria were confirmed, while Gram negative bacteria, yeast, Tick Borne Encephalitis and West Nile Viruses were shown to be insensitive. In addition to antimicrobial activities, the hemolysis effect of def1 and def2 on human erythrocytes was also established.</p> <p>Conclusions</p> <p>Although there is nothing known about the realistic concentration of defensins in <it>I. ricinus </it>tick body, these results suggest that defensins play an important role in defence against different pathogens. Moreover this is a first report of a one amino acid substitution in a defensins molecule and its impact on antimicrobial activity.</p

Antimicrobial and antiborrelial characterization of Dermacentor marginatus defensin.

Ticks, as blood sucking arthropods, are able to transmit various pathogens. Their immune system involves many antimicrobial molecules to fight against them. Among these antimicrobials, defensins, a 5.3 kDa peptides, play an important role in rapid immune answer. In this study we examined the antimicrobial spectrum of Dermacentor marginatus defensin (def DM) with respect to the fact that Dermacentor variabilis ticks are not able to successfully maintain and transmit Borrelia burgdorferi sensu lato, the causative agent of Lyme disease. Expression of the def DM gene was detected in hemolymph, midgut and salivary glands. Defensin was isolated from hemolymph using RP-HPLC and its sequence was determined by mass spectrometry and Edman degradation. Synthetic mature peptide def DM revealed an anti-Gram-positive bacterial role as well as borreliacidal activity, with concentration dependent influence. These results suggest a possible role in the clearing of borrelia spirochetes ingested by D. marginatus ticks

Defensins from the tick Ixodes scapularis are effective against phytopathogenic fungi and the human bacterial pathogen Listeria grayi

Contribution: Study design, molecular analysis and drafting the mansucriptInternational audienceBackground: Ixodes scapularis is the most common tick species in North America and a vector of important pathogens that cause diseases in humans and animals including Lyme disease, anaplasmosis and babesiosis. Tick defensins have been identified as a new source of antimicrobial agents with putative medical applications due to their wide-ranging antimicrobial activities. Two multigene families of defensins were previously reported in I. scapularis. The objective of the present study was to characterise the potential antimicrobial activity of two defensins from I. scapularis with emphasis on human pathogenic bacterial strains and important phytopathogenic fungi. Methods: Scapularisin-3 and Scapularisin-6 mature peptides were chemically synthesised. In vitro antimicrobial assays were performed to test the activity of these two defensins against species of different bacterial genera including Gram-positive bacteria Staphylococcus aureus, Staphylococcus epidermidis, and Listeria spp. as well as Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa along with two plant-pathogenic fungi from the genus Fusarium. In addition, the tissue-specific expression patterns of Scapularisin-3 and Scapularisin-6 in I. scapularis midgut, salivary glands and embryo-derived cell lines were determined using PCR. Finally, tertiary structures of the two defensins were predicted and structural analyses were conducted. Results: Scapularisin-6 efficiently killed L. grayi, and both Scapularisin-3 and Scapularisin-6 caused strong inhibition (IC50 value: similar to 1 mu M) of the germination of plant-pathogenic fungi Fusarium culmorum and Fusarium graminearum. Scapularisin-6 gene expression was observed in I. scapularis salivary glands and midgut. However, Scapularisin-3 gene expression was only detected in the salivary glands. Transcripts from the two defensins were not found in the I. scapularis tick cell lines ISE6 and ISE18. Conclusion: Our results have two main implications. Firstly, the anti-Listeria and antifungal activities of Scapularisin-3 and Scapularisin-6 suggest that these peptides may be useful for (i) treatment of antibiotic-resistant L. grayi in humans and (ii) plant protection. Secondly, the antimicrobial properties of the two defensins described in this study may pave the way for further studies regarding pathogen invasion and innate immunity in I. scapularis