PROSITE documentation PDOC60010

Assassin bug toxin signature

Assassin bugs (Arthropoda:Insecta:Hemiptera:Reduviidae), sometimes known as conenoses or 'kissing bugs', are one of the largest and morphologically diverse families of true bugs feeding on crickets, caterpillars and other insects. Some assassin bug species are bloodsucking parasites of mammals, even of human. They can be commonly found throughout most of the world and their size varies from a few millimeters to as much as 3 or 4 centimeters [1]. The toxic saliva of the predatory assassin bugs contains a complex mixture of small and large peptides for diverse uses such as immobilizing and pre-digesting their prey, and defense against competitors and predators. Assassin bug toxins are small peptides with disulfide connectivity that target ion-channels. They are relatively homologous to the calcium channel blockers omega-conotoxins (see <PDOC60004>) from marine cone snails and belong to the four-loop cysteine scaffold structural class [1,2].

One of these small proteins, Ptu1, blocks reversibly the N-type calcium channels, but at the same time is less specific for the L- or P/Q-type calcium channels [1]. Ptu1 is 34 amino acid residues long and is cross-linked by 3 disulfide bridges. Ptu1 contains a β-sheet region made of 2 antiparallel β-strands and consists of a compact disulfide-bonded core from which four loops emerge as well as N- and C-termini (see <PDB:1I26; A>) [2].

Some assassin bug toxins are listed below:

• Agriosphodrus dohrni toxin Ado1.
• Isyndus obscurus toxin Iob1.
• Peirates turpis toxin Ptu1.

The signature pattern for assassin bug toxins contains six conserved cysteines involved in disulfide bonds within a knottin scaffold [E2].