Nigritoxin is a bacterial toxin for crustaceans and insects

Abstract

The Tetraconata (Pancrustacea) concept proposes that insects are more closely related to aquatic crustaceans than to terrestrial centipedes or millipedes. The question therefore arises whether insects have kept crustacean-specific genetic traits that could be targeted by specific toxins. Here we show that a toxin (nigritoxin), originally identified in a bacterial pathogen of shrimp, is lethal for organisms within the Tetraconata and non-toxic to other animals. X-ray crystallography reveals that nigritoxin possesses a new protein fold of the α/β type. The nigritoxin N-terminal domain is essential for cellular translocation and likely encodes specificity for Tetraconata. Once internalized by eukaryotic cells, nigritoxin induces apoptotic cell death through structural features that are localized in the C-terminal domain of the protein. We propose that nigritoxin will be an effective means to identify a Tetraconata evolutionarily conserved pathway and speculate that nigritoxin holds promise as an insecticidal protein.

Crystal structure of full-length cytotoxic necrotizing factor CNFYreveals molecular building blocks for intoxication

“…The fact that (i) translocation in CNFs also involves two hydrophobic motifs interrupted by acidic residues and (ii) the observation that a sequence that gets cleaved to release the catalytic unit (D4-5) of CNF Y (residues 532 to 544) is not accessible in the full-length structure ( Fig 1C) may hint at a similar unfolding in the CNFs. In this respect, the similarity of parts of the CNF Y 's D1 domain to the putative translocation domain of nigritroxin ( Fig 3A) (Labreuche et al, 2017) is interesting, because the translocation domain of this toxin does not contain hydrophobic α-helices. This could indicate that the translocation process occurs through several steps that involve different parts of the translocation machinery, most of which are not shared between the CNFs and nigritoxin.…”

“…Although the D1 domain of CNF Y is, due to its overall α-helical character, reminiscent of the translocation domain of other toxins such as diphtheria toxin (DT), searches with DALI (Holm & Rosenström, 2010) detected no significant structural homology to these proteins. Instead, it identified only the segment containing the four-stranded anti-parallel β-sheet (residues 152-343) as being somewhat similar to a fragment of the translocation domain of nigritoxin, a toxin of crustaceans and insects (PDB entry 5M41; 177 residues aligned, rmsd 3.8 Å, 11% sequence identity) ( Fig 3A) (Labreuche et al, 2017). However, the translocation domain of nigritoxin is significantly smaller than the D1 domain of CNF Y and does not contain hydrophobic sequence motifs, hinting at distinct translocation mechanisms.…”

“…Nigritoxin is a toxin of crustaceans and insects. The translocation domain of nigritoxin (PDB entry 5M41,(Labreuche et al, 2017)) and domain D1 of CNF Y show partial structural similarity (highlighted areas). This similarity was identified with DALI(Holm & Rosenström, 2010) which was also used to align both structures.B The ART-like domain D4 of CNF Y .…”

Ancestral gene acquisition as the key to virulence potential in environmental Vibrio populations

“…Conjugation between E. coli and Vibrio was performed at 30 °C as described previously [ 36 ]. The BL21(DE3) strains expressing the R5.7_GFP fusion proteins were constructed using the Gibson assembly method (New England Biolabs, NEB) as previously described [ 40 ]. Briefly, the fragment encoding the green fluorescent protein (GFP) was amplified from plasmid pMRB-GFP [ 6 ] (see primer details in Table S 4 ).…”

“…Recombinant R5.7 F12 and R5.7 crass proteins were purified as previously described [ 40 ]. Briefly, after expression of the proteins in ZYP 5052 (20 °C, 72 h) and chemical cell lysis, the lysate was clarified at 13,865 × g for 45 min at 4 °C.…”