Biopesticidal potential of cyclotides: an insight

Cyclotides are cyclic, plant-derived cysteine rich peptides (CRP) with experimentally proven pesticidal activity thus, qualifying them as potential biopesticides. They are preferred over synthetic pesticides for their ecofriendly attributes and are safer for humans and livestock. Their natural role in plants is defense against pests and pathogens. They consist of 26 to 37 amino acids alongwith six cysteine residues that are highly conserved and form three disulfide linkages (Cys(I)-Cys(IV), Cys(II)-Cys(V), Cys(III)-Cys(VI)) producing a knotted ring topology, or the cyclic cystine knot (CCK). This conserved CCK motif protects the cyclotides from heat, chemical and proteolytic degradation making them extremely stable peptides and consequently the ability to resist pest attack on the plant. Their mode of action is by binding, interacting with host cell membrane and eventually disrupting them, thus resulting in pest mortality. Recently the commercialization of bioinsecticidal spray, Sero-X (mix of cyclotides from Clitoria ternatea) to control pests affecting cotton crops, emphasizes the biopesticidal potential of cyclotides. To date more than 750 cyclotides have been discovered, but only 26 cyclotides have been investigated for pesticidal activity against pests affecting crops, animals and humans. Considering the potential of cyclotides, the present review describes pesticidal activity of 26 cyclotides relevant to agricultural crops and animal husbandry. Further, the mechanism of action and implication of multiple bioactivities (hemolytic and cytotoxic) of pesticidal cyclotides for developing commercial biopesticides have been discussed. Future prospects include the importance of screening more numbers of cyclotides against a wider range of pests for formulating biopesticidal sprays.