New insights into lectin from Abelmoschus esculentus seeds as a Kunitz-type inhibitor and its toxic effects on Ceratitis capitata and root-knot nematodes Meloidogyne spp.

Plants produce lectins to confer resistance to pathogens through specific carbohydrate binding. The classification of lectins based only ligands can sometimes obscure other functions intrinsic to its structure. In this work, we characterized Abelmoschus esculentus lectin (AEL) on the basis of structural insights and reported its toxic effects on the Mediterranean fruit fly Ceratitis capitata and root-knot nematodes Meloidogyne incognita and Meloidogyne javanica. LC-MS/MS analysis followed by SPIDER searches and de novo sequencing indicated AEL as a Kunitz-type protease inhibitor homologous to the 21-kDa seed protein of Theobroma cacao, an endopeptidase inhibitor. AEL inhibited the activities of trypsin (Ki = 3.3 nM), chymotrypsin (Ki = 8.3 nM), and papain (Ki = 0.5 mu M) but not cathepsin D. Insecticidal activity was evaluated in the first, second, and third instar larvae and pupae, in which AEL (2000 mu g/mL) was more effective on the pupal stage, showing more toxicity than the organophosphates malathion and dimethoate. AEL (500 mu g/mL) inhibited the hatching of second-stage juveniles in both nematode species, with greater inhibition occurring in M. incognita. The Kunitz-type serine/cysteine protease inhibitor activities of AEL and its pest control effects may provide a novel understanding of its mechanisms in the plant immune system and their biotechnological applications.