C-Type Lectin-20 Interacts with ALP1 Receptor to Reduce Cry Toxicity in Aedes aegypti

Abstract

Aedes aegypti is a crucial vector for human diseases, such as yellow fever, dengue, chikungunya, and Zika viruses. Today, a major challenge throughout the globe is the insufficient availability of antiviral drugs and vaccines against arboviruses, and toxins produced by Bacillus thuringiensis (Bt) are still used as biological agents for mosquito control. The use of Cry toxins to kill insects mainly depends on the interaction between Cry toxins and important toxin receptors, such as alkaline phosphatase (ALP). In this study, we investigated the function of A. aegypti C-type lectin-20 (CTL-20) in the tolerance of Cry toxins. We showed that recombinant CTL-20 protein interacted with both Cry11Aa and ALP1 by the Far-Western blot and ELISA methods, and CTL-20 bound to A. aegypti larval brush border membrane vesicles (BBMVs). Binding affinity of CTL-20 to ALP1 was higher than that of Cry11Aa to ALP1. Furthermore, the survival rate of A. aegypti larvae fed with Cry11Aa toxin mixed with recombinant CTL-20 fusion protein was significantly increased compared with that of the control larvae fed with Cry11Aa mixed with thioredoxin. Our novel results suggest that midgut proteins like CTLs may interfere with interactions between Cry toxins and toxin receptors by binding to both Cry toxins and receptors to alter Cry toxicity.

Knockout of Two Cry-Binding Aminopeptidase N Isoforms Does Not Change Susceptibility of Aedes aegypti Larvae to Bacillus thuringiensis subsp. israelensis Cry4Ba and Cry11Aa Toxins

“…The susceptibility to Bti Cry4Ba and Cry11Aa toxins was determined for different Ae. aegypti strains as described [ 25 ]. At least 5 gradient concentrations of purified Cry4Ba and Cry11Aa protoxins were added to 20 mL filtered water containing 25 early fourth instar larvae and mixed fully.…”

Cloning, expression and activity of ATP-binding protein in Bacillus thuringiensis toxicity modulation against Aedes aegypti

“…At the same time, the membrane with Cry11Aa was also incubated by biotinylated ABP (4 ng/ml), following probed by the primary rabbit polyclonal antibody (1:3000) to biotin and the secondary goat-anti-rabbit-AP-conjugated polyclonal antibody (1:3000). A BCIP/NBT alkaline phosphatase assay kit was used to visualize the binding protein following the manufacturer’s instructions [23].…”

“…C-type lectin-20 was also found to interact with ALP1 to reduce Cry toxicity in Ae. aegypti [23]. Resistance can also be induced by the mutation of ATP-binding cassette (ABC) transporter in Heliothis virescens [24–28].…”

The Tripartite Interaction of Host Immunity–Bacillus thuringiensis Infection–Gut Microbiota

“…It is well known that the interaction between Cry toxin and toxin receptors from the host midgut brush border membrane vesicles (BBMVs) is the initial step in the insecticidal activity of the Cry protein toxins [ 107 , 108 , 109 , 110 ]. Several researchers also showed the interaction between midgut immune-related proteins and Cry toxin [ 111 , 112 , 113 ]. There is evidence showing that immune-related protein like Dorsal and peroxidase C in the midgut juice of P. xylostella and S. exigua can bind to the Cry1Ab1 protein toxin [ 111 ].…”

“…Similarly, it has been reported that C-type lectin-20 (CTL-20) in Aesdes aegyptii has the potential to bind to both toxin receptors and Cry toxins to affect the interactions between Cry toxins and toxin receptors to reduce Cry toxicity in Aedes aegypti [ 112 ]. Similarly, another study on immune-related peptidoglycan recognition protein (PGRP) gene expression and PO activities in Cry1Ac-susceptible and -resistant P. xylostella found that the resistant strain of P. xylostella had higher PO activity compared with the susceptible strain [ 114 ].…”