Drosomycin, an Innate Immunity Peptide of Drosophila melanogaster, Interacts with the Fly Voltage-gated Sodium Channel

Abstract

Several peptide families, including insect antimicrobial peptides, plant protease inhibitors, and ion channel gating modifiers, as well as blockers from scorpions, bear a common CS␣␤ scaffold. The high structural similarity between two peptides containing this scaffold, drosomycin and a truncated scorpion ␤-toxin, has prompted us to examine and compare their biological effects. Drosomycin is the most expressed antimicrobial peptide in Drosophila melanogaster immune response. A truncated scorpion ␤-toxin is capable of binding and inducing conformational alteration of voltage-gated sodium channels. Here, we show that both peptides (i) exhibit anti-fungal activity at micromolar concentrations; (ii) enhance allosterically at nanomolar concentration the activity of Lqh␣IT, a scorpion alpha toxin that modulates the inactivation of the D. melanogaster voltage-gated sodium channel (DmNa v 1); and (iii) inhibit the facilitating effect of the polyether brevetoxin-2 on DmNa v 1 activation. Thus, the short CS␣␤ scaffold of drosomycin and the truncated scorpion toxin can maintain more than one bioactivity, and, in light of this new observation, we suggest that the biological role of peptides bearing this scaffold should be carefully examined. As for drosomycin, we discuss the intriguing possibility that it has additional functions in the fly, as implied by its tight interaction with DmNa v 1.The cysteine-stabilized ␣␤ scaffold, CS␣␤, contains an ␣-helix packed against a two-stranded ␤-sheet stabilized by three spatially conserved disulfide bonds (reviewed in Ref. 1). The CS␣␤ motif appears in a number of polypeptide families that can exert various biological functions such as: short chain (30 -50 residues long) and long chain (60 -76 residues long) scorpion toxins that affect voltage-gated ion channels, antimicrobial peptides (of insect and plants) as well as plant protease inhibitors (see Fig. 1) (2, 3).Analysis of the structure-function relationships of several representatives of a subclass of the long chain scorpion toxins family, the scorpion ␤-toxins (activators of voltage-gated sodium channels (Na v s) 5 ), elucidated their bioactive surfaces including those of the anti-insect excitatory and depressant toxins Bj-xtrIT and LqhIT2 (from Hottentota judaica and Leiurus quinquestriatus hebraeus, respectively (4 -6)) and the antimammalian ␤-toxin Css4 (from Centruroides suffusus suffusus (7)). These studies highlighted a conserved pharmacophore positioned on the CS␣␤ protein core (7). The C-tail, loops, turns, and unstructured stretches that connect to the CS␣␤ protein core in long chain scorpion toxins constitute a large portion of their exteriors and bear residues that participate in bioactivity (reviewed in Ref. 8). We have recently reported that truncated scorpion ␤-toxins, lacking the N-and C-terminal regions of the parental peptides but maintaining the CS␣␤ motif (⌬⌬␤-toxins), are able to interact at high affinity with Na v s (9). Although by themselves, the ⌬⌬␤-toxins (⌬⌬Css4 and ⌬⌬Bj-xtrIT) were nontoxic and did not ...

Peptides as toxins/defensins

“…Anionic and cationic peptides contain disulfide bondforming cysteine residues and are found in drosomycins from fruit fly hemolymph (Cohen et al 2009), human defensins (Schneider et al 2005), and tachyplesins from horseshoe crabs (Muta et al 1990). …”

Age and Diet Affect Genetically Separable Secondary Injuries that Cause Acute Mortality Following Traumatic Brain Injury in Drosophila

“…The transcription mechanism is likely to involve the Toll pathway because Drs is predominantly regulated by the Toll pathway, as are secreted peptide-encoding genes in the Bom family that, like Drs, had age- and diet-regulated expression that negatively correlated with the MI 24 (Lemaitre and Hoffmann 2007; Clemmons et al 2015) (Table 2). The Drs-specific function may be related its ability to inactivate a voltage-gated sodium channel, since blocking upregulation of a sodium channel improves outcomes in a rat TBI model (Cohen et al 2009; Huang et al 2014). …”

Nematode-derived drosomycin-type antifungal peptides provide evidence for plant-to-ecdysozoan horizontal transfer of a disease resistance gene

“…For example, in addition to major antifungal activity, some plant DTAFPs have developed diverse activities as inhibitors of protein translation, enzymes and bacterial growth, mediators of zinc tolerance, and blockers of ion channels 44 . Similarly, drosomycin has been found to gain ability in interacting with the fly voltage-gated sodium channel, possibly acting as a neuropeptide 25 . In C. remanei, cremycin-15 has evolved antibacterial activity described here, while scorpion venom-derived DTAFPs have switched their targets from fungi to animal sodium channels [24][25][26] .…”

“…Similarly, drosomycin has been found to gain ability in interacting with the fly voltage-gated sodium channel, possibly acting as a neuropeptide 25 . In C. remanei, cremycin-15 has evolved antibacterial activity described here, while scorpion venom-derived DTAFPs have switched their targets from fungi to animal sodium channels [24][25][26] . All these observations suggest that the gene can be fixed only in organisms where it developed important functions following gene duplication and speciation.…”

“…Experimental deletion of the NC-domain of a scorpion toxin resulted in antifungal ability of the toxin 25 , whereas the addition of the NC-domain of a toxin on the drosomycin scaffold led to a neurotoxin targeting rat sodium channels 26 . These data provide convincing functional evidence in favour of evolutionary link between drosomycins and scorpion sodium channel toxins, and present an example of divergent evolution occurring in a specific arthropod lineage, in which a DTAFP evolved into a neurotoxin [24][25][26] . The insertion of a small fragment, as the N-turn of the scorpion toxins, in the N-terminal region of a DTAFP is also seen in mehamycin (Fig.…”