Two novel defensin-encoding genes of the Chagas disease vector Triatoma brasiliensis (Reduviidae, Triatominae): Gene expression and peptide-structure modeling

Abstract

Defensins are cysteine-rich peptides involved in the innate immunity of insects and many other organisms. In the present study, two novel defensin-encoding cDNAs and the respective genomic DNAs (def3 and def4) of Triatoma brasiliensis were identified and their tissue-specific and temporal expression was characterized. Both of the deduced mature peptides consisted of 43 amino acid residues and were highly similar to previously identified triatomine defensins (81.4-100%). Semi-quantitative RT-PCR data showed that def3 was constitutively expressed in the fat body and was induced in salivary glands and the small intestine at 5 and 3 days after feeding (daf), respectively. The def4 mRNA level was highly up-regulated in the stomach and fat-body tissues at 5 and 3 daf, respectively. The three-dimensional structures of these defensins were predicted using a homology modeling approach with Def-AAA, the defensin from Anopheles gambiae, as template (62-74% identity). A map of the electrostatic potential of these models revealed that, despite their similar folding patterns, mature Def2 and Def4 have a more cationic structure than is the case for Def1 and Def3. Such differences may orient the antimicrobial profile of these defensins against distinct targets in different organs of the insect.

Humoral responses in Rhodnius prolixus: bacterial feeding induces differential patterns of antibacterial activity and enhances mRNA levels of antimicrobial peptides in the midgut

“…A previous study – based on structural properties – showed a high similarity between R. prolixus DefA and DefB while DefC differed significantly, forming two distinct groups after a phylogenetic analysis [60]. These authors suggested that the various defensins have different functions.…”

Secreted Trypanosome Cyclophilin Inactivates Lytic Insect Defense Peptides and Induces Parasite Calcineurin Activation and Infectivity

“…4), which contributes to enhanced parasite infectivity. We hypothesize that the interaction of cyclophilin 19 with other protein ligands, such as proline-containing defensin-like peptides (5,62,63) or ␣-globin (1, 29, 51), may also contribute to aspects of in vivo parasite differentiation.…”

Immune homeostasis to microorganisms in the guts of triatomines (Reduviidae): a review

“…Other factors that affect trypanosome development are the AMPs of the insect vector and only defensins have been found in triatomines, such as R. prolixus and T. brasiliensis (Lopez et al 2003, Araújo et al 2006, Waniek et al 2009). Defensins mainly lyse Gram + bacteria, but they can also kill Gram -bacteria, fungi and parasites (Boulanger et al 2006).…”

“…Defensins mainly lyse Gram + bacteria, but they can also kill Gram -bacteria, fungi and parasites (Boulanger et al 2006). In triatomines, different isoforms of defensins have been observed (Lopez et al 2003, Araújo et al 2006, Waniek et al 2009). In R. prolixus, defensin genes are expressed after bacterial inoculations and the activation of immune responses increases the gene transcription in the fat body and the gut (Lopez et al 2003).…”