Abstract
Cyclotides are a family of plant-derived cyclic peptides comprising six conserved cysteine residues connected by three intermolecular disulfide bonds that form a knotted structure known as a cyclic cystine knot (CCK). This structural motif is responsible for the pronounced stability of cyclotides against chemical, thermal, or proteolytic degradation and has sparked growing interest in this family of peptides. Here, we isolated and characterized a novel cyclotide from Palicourea rigida (Rubiaceae), which was named parigidin-br1. The sequence indicated that this peptide is a member of the bracelet subfamily of cyclotides. Parigidin-br1 showed potent insecticidal activity against neonate larvae of Lepidoptera (Diatraea saccharalis), causing 60% mortality at a concentration of 1 μm but had no detectable antibacterial effects. A decrease in the in vitro viability of the insect cell line from Spodoptera frugiperda (SF-9) was observed in the presence of parigidin-br1, consistent with in vivo insecticidal activity. Transmission electron microscopy and fluorescence microscopy of SF-9 cells after incubation with parigidin-br1 or parigidin-br1-fluorescein isothiocyanate, respectively, revealed extensive cell lysis and swelling of cells, consistent with an insecticidal mechanism involving membrane disruption. This hypothesis was supported by in silico analyses, which suggested that parigidin-br1 is able to complex with cell lipids. Overall, the results suggest promise for the development of parigidin-br1 as a novel biopesticide.
Highlights
Cyclotides are a family of plant-derived defense peptides
To understand more about the expression of cyclotides, we investigated their distribution in different parts of P. rigida as well as the influence of climatic variations
The first systematic study to monitor cyclotide expression in different climatic regions was performed for cyclotides expressed in Violaceae species cultivated in Australia and Sweden
Summary
Cyclotides are a family of plant-derived defense peptides. Results: Parigidin-br, a novel cyclotide, shows insecticidal activity in vivo and in vitro. Cyclotides are a family of plant-derived cyclic peptides comprising six conserved cysteine residues connected by three intermolecular disulfide bonds that form a knotted structure known as a cyclic cystine knot (CCK). Based on studies that show the tendency of cyclotides to form tetramers and octamers [27], it is probable that these peptides accumulate on the membrane surface where they form multimeric structures, leading to pores, resulting in membrane disruption and alteration of the osmotic balance These effects lead to lower food absorption, impaired larval development, and higher insect mortality [26, 28, 29]. The relationship between structure and function was explored to determine the specificity of parigidin-br, which appears to be a promising insecticidal agent
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