Insecticide activity of a peptidase inhibitor isolated from Anadenanthera macrocarpa seeds against Anagasta kuehniella

Abstract

Protease inhibitors (PIs) are a part of the plant defense system and reduce the proteolytic activity of the digestive enzymes of insect pests. The current study aimed to isolate and characterize an inhibitor of trypsin (AmTI) within the seed of Anadenanthera macrocarpa (Benth) (Leguminosae-Mimosoideae). Moreover, we tried to assess the defense mechanism of the larvae of Anagasta kuehniella against this inhibitor. Protein seed extracts were purified using Sephadex G-50 and trypsin-Sepharose columns. Electrophoresis revealed the molecular weight of the inhibitor to be 25 kDa. The stability evaluation demonstrated that the inhibitor was not denatured at temperatures of up to 60 °C, pH 2-10, and concentrations of up to 100 mM dithiothreitol for one hour. The inhibitor reacted in a 1:1 ratio with bovine trypsin with an inhibition constant [Ki] = 2.517 ´ 10-8. Incorporating the inhibitor in a 1 mg per 100 mg proportion of artificial diet offered to A. kuehniella larvae led to a significant difference in the weight and survival of larvae of the fourth instar compared to the control. AmTI acted on the enzymatic activities of trypsin and chymotrypsin, not allowing until the fourth larval instar, A. kuehniella, to create adaptations against the inhibitor, as it had a simultaneous effect on larval weight and mortality. Therefore, a new trypsin inhibitor showing inhibitory activity against the digestive enzymes trypsin and chymotrypsin from A. kuehniella was isolated, indicating that these activities are correlated with the deleterious effects of this insect.