Identification and localization of the set of serine peptidases and their homologs in the larval midgut of <i>Tenebrio molitor</i> L

Peptidases play a key role in the metabolism of proteins and peptides. In this work, we studied the spectrum of midgut serine peptidases (SPs) and serine peptidase homologs (SPHs) in the IV instar larvae of the yellow mealworm Tenebrio molitor using biochemical and proteomic approaches. Seventeen SPs were isolated from the larval midgut of T. molitor and identified using MALDI-TOF MS analyses and genomic and transcriptomic data. The proteins were isolated separately from the anterior part (AM) and the posterior part of the midgut (PM) using size-exclusion chromatography, specific chromogenic and fluorogenic substrates and PAGE under native conditions. Of the 17 SPs, 3 were trypsins, 10 chymotrypsin-like, and 4 elastase-like. Three SPs were localized only in the AM, five SPs in the PM and nine SPs were identified both in AM and PM. In addition, six SPHs with 1-3 substitutions in the catalytic amino acid residues were identified. The majority of analysed proteins had a high level of mRNA expression specific to the feeding stages of development. The results obtained suggest that T. molitor larvae possess a wide range of digestive SPs and SPHs, which may provide them with high resistance to numerous dietary or insecticidal SP inhibitors, as well as indicate wide possibilities for their use for biotechnological production of T. molitor food/feed hydrolysates of this edible insect with increased digestibility, reduced allergenicity and possibly new biological activities.