Cathepsins L and B in Dysdercus peruvianus, Rhodnius prolixus, and Mahanarva fimbriolata. Looking for enzyme adaptations to digestion

Comparative Transcriptomic Analysis Reveals Adaptation Mechanisms of Bean Bug Riptortus pedestris to Different Food Resources

The bean bug, Riptortus pedestris (Hemiptera: Heteroptera), poses a significant threat to soybean production, resulting in substantial crop losses. Throughout the soybean cultivation period, these insects probe and suck on various parts of plants, including leaves, pods, and beans. However, the specific mechanisms by which they adapt to different food resources remain unknown. In this study, we conducted gut transcriptomic analyses of R. pedestris fed with soybean leaves, pods, and beans. A total of 798, 690, and 548 differently expressed genes (DEGs) were monitored in G-pod vs. G-leaf (comparison of insect feeding on pods and leaves), G-bean vs. G-leaf (comparison of insect feeding on beans and leaves), and G-pod vs. G-bean (comparison of insect feeding on pods and beans), respectively. When fed on pods and beans, there was a significant increase in the expression of digestive enzymes, particularly cathepsins, serine proteases, and lipases. Conversely, when soybean leaves were consumed, detoxification enzymes, such as ABC transporters and 4-coumarate-CoA ligase, exhibited higher expression. Our findings indicate that R. pedestris dynamically regulates different metabolic pathways to cope with varying food resources, which may contribute to the development of effective strategies for managing this pest.

Post-feeding transcriptomics reveals essential genes expressed in the midgut of the desert locust

The digestive tract constitutes an important interface between an animal's internal and external environment. In insects, available gut transcriptome studies are mostly exploratory or look at changes upon infection or upon exposure to xenobiotics, mainly performed in species belonging to holometabolan orders, such as Diptera, Lepidoptera or Coleoptera. By contrast, studies focusing on gene expression changes after food uptake and during digestion are underrepresented. We have therefore compared the gene expression profiles in the midgut of the desert locust, Schistocerca gregaria, between three different time points after feeding, i.e., 24 h (no active digestion), 10 min (the initial stage of feeding), and 2 h (active food digestion). The observed gene expression profiles were consistent with the polyphagous herbivorous lifestyle of this hemimetabolan (orthopteran) species. Our study reveals the upregulation of 576 genes 2 h post-feeding. These are mostly predicted to be associated with digestive physiology, such as genes encoding putative digestive enzymes or nutrient transporters, as well as genes putatively involved in immunity or in xenobiotic metabolism. The 10 min time point represented an intermediate condition, suggesting that the S. gregaria midgut can react rapidly at the transcriptional level to the presence of food. Additionally, our study demonstrated the critical importance of two transcripts that exhibited a significant upregulation 2 h post-feeding: the vacuolar-type H(+)-ATPase and the sterol transporter Niemann-Pick 1b protein, which upon RNAi-induced knockdown resulted in a marked increase in mortality. Their vital role and accessibility via the midgut lumen may make the encoded proteins promising insecticidal target candidates, considering that the desert locust is infamous for its huge migrating swarms that can devastate the agricultural production in large areas of Northern Africa, the Middle East, and South Asia. In conclusion, the transcriptome datasets presented here will provide a useful and promising resource for studying the midgut physiology of S. gregaria, a socio-economically important pest species.

Digestive α-L-fucosidase activity in Rhodnius prolixus after blood feeding: effect of secretagogue and nutritional stimuli

Introduction: Rhodnius prolixus (Hemiptera: Reduviidae) is an important vector of Trypanosoma cruzi, the causative agent of Chagas Disease. This insect is a model for the study of insect physiology, especially concerning the digestion of blood. Among the enzymes produced in the midgut of R. prolixus after blood feeding there is a α-L-fucosidase activity. There are very few studies on α-L-fucosidase of insects, and the role of R. prolixus α-L-fucosidase is still not clear. In this work, we tested if the mechanism for production of this enzyme is similar to the observed for proteases, a secretatogue mechanism that respond to the protein contents of the meal. Methods: We tested if specific proteins or sugars elicit this response, which may help to understand the nature of the physiological substrate for this enzyme. Results: In general, our results showed that the Anterior Midgut was the only midgut fraction that responds to the blood meal in terms of α-L-fucosidase production. Besides that, this response was not triggered by midgut distension or by ingestion of the blood cell fraction. Conversely, the enzyme was produced after feeding with the plasma fraction. However, the production of α-L-fucosidase was also triggered by different biochemical stimuli, as protein or fucoidan ingestion. Discussion: This suggested that the production of the enzyme in the anterior midgut was a general physiological response under control of different convergent signals. Besides that, the comparison between different treatments for artificial blood feeding showed that heparinated blood was the choice with minor side effects for the study of the midgut α-L-fucosidase, when compared to defibrinated or citrated blood.

Recombinant Cathepsin L of Tribolium castaneum and Its Potential in the Hydrolysis of Immunogenic Gliadin Peptides

Wheat gliadins contain a large amount of glutamine- and proline-rich peptides which are not hydrolyzed by human digestive peptidases and can cause autoimmune celiac disease and other forms of gluten intolerance in predisposed people. Peptidases that efficiently cleave such immunogenic peptides can be used in enzyme therapy. The stored product insect pest Tribolium castaneum efficiently hydrolyzes gliadins. The main digestive peptidase of T. castaneum is cathepsin L, which is from the papain C1 family with post-glutamine cleavage activity. We describe the isolation and characterization of T. castaneum recombinant procathepsin L (rpTcCathL1, NP_001164001), which was expressed in Pichia pastoris cells. The activation of the proenzyme was conducted by autocatalytic processing. The effects of pH and proenzyme concentration in the reaction mixture on the processing were studied. The mature enzyme retained high activity in the pH range from 5.0 to 9.0 and displayed high pH-stability from 4.0 to 8.0 at 20 °C. The enzyme was characterized according to electrophoretic mobility under native conditions, activity and stability at various pH values, a sensitivity to various inhibitors, and substrate specificity, and its hydrolytic effect on 8-, 10-, 26-, and 33-mer immunogenic gliadins peptides was demonstrated. Our results show that rTcCathL1 is an effective peptidase that can be used to develop a drug for the enzyme therapy of various types of gluten intolerance.

Recruitment of lysosomal cathepsins B, L and D as digestive enzymes in Coleoptera

The recruitment of the lysosomal cathepsins B (CAB), L (CAL) and D (CAD) as luminal digestive enzymes was investigated in 3 species of beetles. Gene expression was determined by RNA-seq in different regions of the midgut and in the carcasses from the transcriptomes of Dermestes maculatus, Tenebrio molitor and Zabrotes subfasciatus. These data together with phylogenetic analyses, allowed us to identify the sequences of the gene coding for digestive and lysosomal CABs, CADs and CALs in T. molitor and Z. subfasciatus and observe the absence of digestive cathepsins in D. maculatus. Comparisons of structures based on the overall similarity of modelled structures were performed and subsite residues in the lysosomal and digestive CALs were identified by molecular docking. The data showed that S2 subsites are very variable, probably as an adaption to a luminal digestive role. The survey of sequences of the gene coding for cathepsins in the genomes of 13 beetle species from different phylogenetic groups showed that expansion of CAL and CAB genes occurred only in the Cucujiformia clade. Several digestive CABs have a reduced occluding loop, probably to act as digestive enzymes. Pollen-feeding was proposed to be the selective pressure to recruit cathepsins as digestive enzymes in Cucujiformia beetles.

Proteases inhibitors-insensitive cysteine proteases allow Nezara viridula to feed on growing seeds of field-grown soybean

The southern green stink bug, Nezara viridula is one of the primary soybean pests and causes significant economic losses around the world. In spite of the high proteases inhibitor (PI) levels, N. viridula can feed on developing seeds of field-grown soybean and reduce crop yields. Although the PI-induced responses have been extensively investigated in many pest insects, there is lack of knowledge about the mechanisms that stink bugs employ to withstand cysteine PIs of soybean seeds. This study demonstrated that feeding on developing seeds of field-grown soybean inhibited total proteases activity of N. viridula, as result of inhibition of cathepsin B-like activity in the gut. In addition, from the 30 digestive cathepsins recognized in this study, 6 were identified as cathepsin B-like. Stink bugs that fed on growing seeds of field-grown soybean had similar gut pH to those reared in the laboratory, and both cathepsin B- and L-like had an optima pH of 6.5. Therefore, using specific proteases inhibitors we found that the main proteolytic activity in the gut is from cysteine proteases when N. viridula feeds on soybean crops. Since cathepsin L-like activity was not inhibited by soybean PIs, our results suggested that N. viridula relays on cathepsin L-like to feed on soybean. To our knowledge no study before has shown the impact of seed PIs of field-grown soybean on digestive proteases (cathepsin B- and L-like) of N. viridula. This study suggests that the activity of PI-insensitive cathepsins L-like in the gut would be part of an adaptive strategy to feed on developing soybean seeds. In agreement, the expansions of cathepsin L-like complement observed in pentatomids could confer to the insects a higher versatility to counteract the effects of different PIs.