Purification of active trypsin in the digestive process of insects is essential for the development of potent protease inhibitors (PIs) as an emerging pest control technology and research into insect adaptations to dietary PIs. An important aspect is the presence of proteolytic microorganisms, which contribute to host nutrition. Here, we purified trypsins produced by bacteria Bacillus cereus, Enterococcus mundtii, Enterococcus gallinarum, and Staphylococcus xylosus isolated from the midgut of Anticarsia gemmatalis. The trypsins had a molecular mass of approximately 25 kDa. The enzymes showed increased activity at 40°C, and they were active at pH values 7.5-10. Aprotinin, bis-benzamidine, and soybean Kunitz inhibitor (SKTI) significantly inhibited trypsin activity. The l-1-tosyl-amido-2-phenylethylchloromethyl ketone (TPCK), pepstatin A, E-64, ethylenediamine tetraacetic acid, and calcium ions did not affect the enzyme activity at the concentrations tested. We infer the purified trypsins do not require calcium ions, by which they differ from the trypsins of other microorganisms and the soluble and insoluble trypsins characterized from A. gemmatalis. These data suggest the existence of different isoforms of trypsin in the velvetbean caterpillar midguts.

Soybean is one of most consumed and produced grains in the world, and Anticarsia gemmatalis is a pest that causes great damage to this crop due to severe defoliation during its larval phase. Plants have mechanisms that lead to the inhibition of proteases in the intestine of these herbivores, hampering their development. Understanding this complex protease inhibitor is important for pest control. The objective of this study was to evaluate the enzymatic profiles of the intestinal proteases of the soybean caterpillar at different instars. For this, the proteolytic profile of the gut in the third, fourth, and fifth instars were analyzed.Irreversible inhibitors of proteases were separately incubated with A. gemmatalis enzyme extracts at the third, fourth, and fifth instar to assess the contribution of these proteases to total proteolytic activity. The enzymatic extracts were also evaluated with specific substrates to confirm changes in the specific activities of trypsin-like, chymotrypsin-like, and cysteine proteases at different instars. The results showed that the protease profile of A.gemmatalis gut changes throughout its larval development.The activity of cysteine proteases was more intense in the first instar. On the contrary, the serine proteases The protease profile of the gut of A. gemmatalis changes throughout larval development. In the third instar, cysteine protease activity is predominant over others. In the fourth and fifth instars, proteolytic activity is mainly due to serine proteases. This difference in activity in the different instars of A. gemmatalis suggests that the expression of the genes coding for proteases also changes throughout the development of the insect. Using serine PIs is a good strategy for controlling insect pests, as these are the main proteolytic enzymes of Lepidoptera. However, the presence of other important protease subclasses in insect digestibility suggests that a combination of serine and cysteine PIs may be promising, aiming to compromise larval development at different instars.

BACKGROUND Anticarsia gemmatalis larvae are key defoliating pests of soybean plants. Inorganic insecticides, harmful to the environment and human health, are the main molecules used in the control of this pest. To apply more sustainable management methods, organic molecules with high specificities, such as proteinaceous protease inhibitors, have been sought. Thus, molecular docking studies, kinetics assays, and biological tests were performed to evaluate the inhibitory activity of two peptides (GORE1 and GORE2) rationally designed to inhibit trypsin‐like enzymes, which are the main proteases of A. gemmatalis midgut. RESULTS The molecular docking simulations revealed critical hydrogen bonding patterns of the peptides with key active site residues of trypsin‐like proteases of A. gemmatalis and other Lepidopteran insects. The negative values of binding energy indicate that hydrogen bonds potentiate the tight binding of the peptides with trypsin‐like proteases, predicting an effective inhibition. The inhibition's rate constants (Ki) were 0.49 and 0.10 mM for GORE1 and GORE2, resulting in effective inhibition of the activity trypsin on the L‐BApNA substrate in the in vitro tests, indicating that the peptide GORE2 has higher inhibitory capacity on the A. gemmatalis trypsins. In addition, the two peptides were determined to be reversible competitive inhibitors. The in vivo test demonstrated that the peptides harm the survival and development of A. gemmatalis larvae. CONCLUSION These results suggest that these peptides are potential candidates in the management of A. gemmatalis larvae and provide baseline information for the design of new trypsin‐like inhibitors based on peptidomimetic tools. © 2020 Society of Chemical Industry

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Insects overcome the action of natural protease inhibitors (PIs) due to evolutionary adaptations through endogenous proteolysis and reprogramming proteases. Insect adaptations complicate the formulation of IP‐based crop protection products. However, small peptides designed based on the active site of enzymes have shown promising results that could change this scenario. GORE1 and GORE2 are designed tripeptides that reduce the survival of Anticarsia gemmatalis when ingested orally. In this article, the stability and ability of the peptides to bind trypsin‐like enzymes of A. gemmatalis were evaluated by molecular dynamics (MD) simulations. The ability of the peptides to inhibit trypsin‐like enzymes in vivo was compared with the SKTI protein by feeding A. gemmatalis larvae at different concentrations, followed by an inhibition persistence assay. During the MD simulation of enzyme–ligand complexes, both peptides showed a small variation of root‐mean‐square deviation and root‐mean‐square fluctuation, suggesting that these molecules reach equilibrium when forming a complex with the trypsin‐like enzyme. Furthermore, both peptides form hydrogen bonds with substrate recognition sites of A. gemmatalis trypsin‐like enzyme, with GORE2 having more interactions than GORE1. Larvae of A. gemmatalis exposed to the peptides and SKTI showed a similar reduction in proteolytic activity, but the persistence of inhibition of trypsin‐like enzyme was longer in peptide‐fed insects. Despite their size, the peptides exhibit important active and substrate binding site interactions, stability during complex formation, and steadiness effects in vivo. The results provide fundamental information for the development of mimetic molecules and help in decision‐making for the selection of delivery methods for larger‐scale experiments regarding similar molecules.

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