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

Cysteine peptidases (CP) play a role as digestive enzymes in hemipterans similar to serine peptidases in most other insects. There are two major CPs: cathepsin L (CAL), which is an endopeptidase and cathepsin B (CAB) that is both an exopeptidase and a minor endopeptidase. There are thirteen putative CALs in Dysdercus peruvianus, which in some cases were confirmed by cloning their encoding genes. RNA-seq data showed that DpCAL5 is mainly expressed in the anterior midgut (AM), DpCAL10 in carcass (whole body less midgut), suggesting it is a lysosomal enzyme, and the other DpCALs are expressed in middle (MM) and posterior (PM) midgut. The expression data were confirmed by qPCR and enzyme secretion to midgut lumen by a proteomic approach. Two CAL activities were isolated by chromatography from midgut samples with similar kinetic properties toward small substrates. Docking analysis of a long peptide with several DpCALs modeled with digestive Tenebrio molitor CAL (TmCAL3) as template showed that on adapting to luminal digestion DpCALs (chiefly DpCAL5) changed in relation to their ancestral lysosomal enzyme (DpCAL10) mainly at its S2 subsite. A similar conclusion arrived from structure alignment-based clustering of DpCALs based on structural similarity of the modeled structures. Changes mostly on S2 subsite could mean the enzymes turn out less peptide-bond selective, as described in TmCALs. R. prolixus CALs changed on adapting to luminal digestion, although less than DpCALs. Both D. peruvianus and R. prolixus have two digestive CABs which are expressed in the same extension as CALs, in the first digestive section of the midgut, but less than in the other midgut sections. Mahanarva fimbriolata does not seem to have digestive CALs and their digestive CABs are mainly expressed in the first digestive section of the midgut and do not diverge much from their lysosomal counterparts. The data suggest that CABs are necessary at the initial stage of digestion in CP-dependent Hemipterans, which action is completed by CALs with low peptide-bond selectivity in Heteroptera species. In M. fimbriolata protein digestion is supposed to be associated with the inactivation of sap noxious proteins, making CAB sufficient as digestive CP. Hemipteran genomes and transcriptome data showed that CALs have been recruited as digestive enzymes only in heteropterans, whereas digestive CABs occur in all hemipterans.

ß-glucosidase from Hevea brasiliensis seeds: Purification, homology modeling, and insights into the substrate-binding model.

The isolation of ß-glucosidase from Hevea brasiliensis (Hbglu) seeds was investigated and a homology model was built on the MODELLER software to understand the structure feature. The quality of the model was evaluated on PROCHEK. The refined model was used for molecular docking on AutoDock 4.2 to determine the substrate- binding sites and potential substrates based on their calculated binding affinities. The substrate specificity of Hbglu was verified through the kinetic measurement of hydrolytic activities. Molecular dynamic simulations of cyanogenic ß-glucosidase and ligand-bound complex showed that the free energy (ΔG) for the binding of p-nitrophenyl-ß-D-glucopyranoside and daidzein-7-O-ß-D-glucoside were -8.6 and -7.92 kcal/mol, respectively. Thus, daidzein-7-O-ß-D-glucoside is a potential substrate. Future studies on the physicochemical properties and catalytic mechanisms will provide information on the molecular biological properties of Hbglu. PRACTICAL APPLICATIONS: This study reported the 3D structural simulation of ß-glucosidase from Hbglu. The docking condition between Hbglu and various different substrates were assessed on Autodock. The results can be used as reference in designing enzymes, and improving the utilization of ß-glucosidases for the hydrolysis of flavor precursors from fruits, teas, and wines and for the production of flavonoid compounds and cyanogenic glycoside degradation.