A termiticidal and high denaturation-resistant lectin from Moringa oleifera seed cake

Abstract

Moringa oleifera seed cake contains a lectin named WSMoL_C, which was previously described as an insecticidal agent against the yellow fever mosquito Aedes aegypti. In this study, we evaluated the structural stability of WSMoL_C against denaturation by chemical and physical agents, as well as its insecticidal activity against the termite Nasutitermes corniger. Conformational alterations of WSMoL_C, when in the presence of urea or whilst subjected to heating or high pressures were monitored by circular dichroism and fluorometric analysis. Termiticidal activity was evaluated by supplying the insects with a diet of varying concentrations of WSMoL_C. The effects of WSMoL_C on insect digestive enzymes activities were also determined. Treatment with urea at concentrations of 4 M or less led to a conformational rearrangement of WSMoL_C, as hydrophobic surfaces had less exposure to water. However, at urea concentrations more than 4 M the hydrophobic pockets of WSMoL_C experienced greater exposure to water resulting in a 50 % loss of secondary structure. When subjected to heating of up to 65 °C or pressures up to 2.7 kbar, no conformational changes were detected. WSMoL_C was shown to display insecticidal activity for N. corniger workers and soldiers (LC₅₀ of 0.292 and 0.637 mg/mL, respectively). It was shown from gut extracts of these insects that the lectin inhibited exoglucanase and endoglucanase enzymes. In conclusion, WSMoL_C can be explored as an alternative for termite control because of its high structural stability and ability to withstand denaturation.