Primary digestive cathepsins L of Tribolium castaneum larvae: Proteomic identification, properties, comparison with human lysosomal cathepsin L.

We previously described the most highly expressed enzymes from the gut of the red flour beetle, Tribolium castaneum, as cathepsins L. In the present study, two C1 family-specific cysteine cathepsin L enzymes from the larval midgut were isolated and identified using MALDI-TOF MS analysis. The isolated T. castaneum cathepsins were characterized according to their specificity against chromogenic and fluorogenic peptide substrates, and the most efficiently hydrolyzed substrate was Z-FR-pNA with Arg in the P1 subsite. The specificity of insect digestive cathepsins was compared with human lysosomal cathepsin L, the well-studied peptidase of the C1 family cathepsins. T. castaneum digestive cathepsins efficiently hydrolyzed substrates with small and uncharged amino acid residues at P1 (Ala, Gln) more than human cathepsin L. In particular, these insect digestive cathepsins cleaved with higher efficiency the analogs of immunogenic peptides of gliadins, which contribute to autoimmune celiac disease in susceptible people, and thus insect enzymes may be useful in enzymatic treatments for this disease. A bioinformatic study supported by the proteomic analysis of the primary structures of the isolated cathepsins was used to compare tertiary models. The phylogenetic analysis of coleopteran and human cathepsins from the L subfamily indicated that insect digestive cathepsins grouped separately from lysosomal cathepsins.

RNA interference and dietary inhibitors induce a similar compensation response in Tribolium castaneum larvae.

Tribolium castaneum is a major agriculture pest damaging stored grains and cereal products. The T. castaneum genome contains 26 cysteine peptidase genes, mostly cathepsins L and B, and seven have a major role in digestion. We targeted the expression of the most highly expressed cathepsin L gene on chromosome 10, TC011001, by RNA interference (RNAi), using double-stranded RNA (dsRNA) constructs of different regions of the gene (3', middle, 5' and entire coding regions). RNA sequencing and quantitation (RNA-seq) was used to evaluate knockdown and specificity amongst the treatments. Overall, target gene expression decreased in all treatment groups, but was more severe and specific in dsRNA targeting the 3' and entire coding regions, encoding the proteolytic active site in the enzyme. Additional cysteine cathepsin genes also were down-regulated (off-target effects), but some were up-regulated in response to RNAi treatment. Notably, some serine peptidase genes were increased in expression, especially in dsRNA targeting 5' and middle regions, and the response was similar to the effects of dietary cysteine protease inhibitors. We manually annotated these serine peptidase genes to gain insight into function and relevance to the RNAi study. The data indicate that T. castaneum larvae compensate for the loss of digestive peptidase activity in the larval gut, regardless of the mechanism of disruption.

Cysteine digestive peptidases function as post-glutamine cleaving enzymes in tenebrionid stored-product pests.

The major storage proteins in cereals, prolamins, have an abundance of the amino acids glutamine and proline. Storage pests need specific digestive enzymes to efficiently hydrolyze these storage proteins. Therefore, post-glutamine cleaving peptidases (PGP) were isolated from the midgut of the stored-product pest, Tenebrio molitor (yellow mealworm). Three distinct PGP activities were found in the anterior and posterior midgut using the highly-specific chromogenic peptide substrate N-benzyloxycarbonyl-L-Ala-L-Ala-L-Gln p-nitroanilide. PGP peptidases were characterized according to gel elution times, activity profiles in buffers of different pH, electrophoretic mobility under native conditions, and inhibitor sensitivity. The results indicate that PGP activity is due to cysteine and not serine chymotrypsin-like peptidases from the T. molitor larvae midgut. We propose that the evolutionary conservation of cysteine peptidases in the complement of digestive peptidases of tenebrionid stored-product beetles is due not only to the adaptation of insects to plants rich in serine peptidase inhibitors, but also to accommodate the need to efficiently cleave major dietary proteins rich in glutamine.

Complex of digestive proteinases of Galleria mellonella Caterpillars: composition, properties, and limited proteolysis of Bacillus thuringiensis endotoxins.

The complex of digestive proteinases in caterpillars of the greater wax moth Galleria mellonella was studied. Using chromogenic substrates and inhibitor analysis, it was found that serine proteinases play a key role in this complex. Three anionic and two cationic forms of trypsin and one anionic and one cationic form of chymotrypsin were identified by zymography in the midgut extract of G. mellonella. The most active trypsin was purified to electrophoretic homogeneity, and its N-terminal amino acid sequence was shown to be identical to that of mature trypsin from Plodia interpunctella. Midgut extract from G. mellonella was capable of processing Cry-proteins from Bacillus thuringiensis ssp. galleriae. Enzymes with tryptic and chymotryptic activities participate in this process, and activation of protoxin Cry9A is not the rate-limiting stage in the toxic action of this protein on the greater wax moth.

Digestive proteolysis organization in two closely related Tenebrionid beetles: red flour beetle (Tribolium castaneum) and confused flour beetle (Tribolium confusum).

The spectra of Tribolium castaneum and T. confusum larval digestive peptidases were characterized with respect to the spatial organization of protein digestion in the midgut. The pH of midgut contents in both species increased from 5.6-6.0 in the anterior to 7.0-7.5 in the posterior midgut. However, the pH optimum of the total proteolytic activity of the gut extract from either insect was pH 4.1. Approximately 80% of the total proteolytic activity was in the anterior and 20% in the posterior midgut of either insect when evaluated in buffers simulating the pH and reducing conditions characteristic for each midgut section. The general peptidase activity of gut extracts from either insect in pH 5.6 buffer was mostly due to cysteine peptidases. In the weakly alkaline conditions of the posterior midgut, the serine peptidase contribution was 31 and 41% in T. castaneum and T. confusum, respectively. A postelectrophoretic peptidase activity assay with gelatin also revealed the important contribution of cysteine peptidases in protein digestion in both Tribolium species. The use of a postelectrophoretic activity assay with p-nitroanilide substrates and specific inhibitors revealed a set of cysteine and serine endopeptidases, 8 and 10 for T. castaneum, and 7 and 9 for T. confusum, respectively. Serine peptidases included trypsin-, chymotrypsin-, and elastase-like enzymes, the latter being for the first time reported in Tenebrionid insects. These data support a complex system of protein digestion in the Tribolium midgut with the fundamental role of cysteine peptidases.

[Properties of post-proline cleaving enzymes from Tenebrio molitor].

Two post-proline cleaving enzymes PRE1 and PRE2 with molecular masses of 101 and 62 kDa, respectively, capable of hydrolyzing Z-AlaAlaPro-pNA were isolated for the first time from the midgut of the flour beetle Tenebrio molitor and characterized. PRE1 is active only in acidic media, with a maximum at pH 5.6, whereas PRE2, both in acidic and alkaline media with a maximum at pH 7.9. Using inhibitory analysis, both PRE1 and PRE2 were shown to belong to serine peptidases. Some data indicate that a Cys residue is located close to the PRE2 active site. Z-Pro-prolinal, a specific inhibitor of prolyl oligopeptidases, inhibits completely PRE2 and partially PRE1. The substrate specificities of the isolated enzymes were studied. It was shown that Z-AlaAla-Pro-pNA was the best substrate for PRE1, and Z-AlaPro-pNA, for PRE2. The combination of the studied properties allowed characterization of PRE2 as a prolyl oligopeptidase.

Sequence analysis and molecular characterization of larval midgut cDNA transcripts encoding peptidases from the yellow mealworm, Tenebrio molitor L.

Peptidase sequences were analysed in randomly picked clones from cDNA libraries of the anterior or posterior midgut or whole larvae of the yellow mealworm, Tenebrio molitor Linnaeus. Of a total of 1528 sequences, 92 encoded potential peptidases, from which 50 full-length cDNA sequences were obtained, including serine and cysteine proteinases and metallopeptidases. Serine proteinase transcripts were predominant in the posterior midgut, whereas transcripts encoding cysteine and metallopeptidases were mainly found in the anterior midgut. Alignments with other proteinases indicated that 40% of the serine proteinase sequences were serine proteinase homologues, and the remaining ones were identified as either trypsin, chymotrypsin or other serine proteinases. Cysteine proteinase sequences included cathepsin B- and L-like proteinases, and metallopeptidase transcripts were similar to carboxypeptidase A. Northern blot analysis of representative sequences demonstrated the differential expression profile of selected transcripts across five developmental stages of Te. molitor. These sequences provide insights into peptidases in coleopteran insects as a basis to study the response of coleopteran larvae to external stimuli and to evaluate regulatory features of the response.

Fractionation of digestive proteinases from Tenebrio molitor (Coleoptera: Tenebrionidae) larvae and role in protein digestion.

Tenebrio molitor larval digestive proteinases were purified and characterized by gel filtration chromatography combined with activity electrophoresis. Cysteine proteinases, consisting of at least six distinct activities, were found in three chromatographic peaks in anterior and posterior midgut chromatographies. The major activity in the anterior midgut, peak cys II, consisted of cysteine proteinases with Mm of 23 kDa. The predominant peak in the posterior, cys I, was represented by 38 kDa proteinases. The activities of all cysteine proteinases were maximal in buffers from pH 5.0 to 7.0, with 80% stability at pH values from 4.0 to 7.0. In the conditions of the last third of the midgut, the activity and stability of cysteine proteinases was sharply decreased. Trypsin-like activity included a minor peak of "heavy" trypsins with Mm 59 kDa, located mainly in the anterior midgut. An in vitro study of the initial stages of digestion of the main dietary protein, oat 12S globulin, by anterior midgut proteinases revealed that hydrolysis occurred through the formation of intermediate high-Mm products, similar to those formed during oat seed germination. Cysteine proteinases from the cys III peak and heavy trypsins were capable of only limited proteolysis of the protein, whereas incubation with cys II proteinases resulted in substantial hydrolysis of the globulin.

Diversity of digestive proteinases in Tenebrio molitor (Coleoptera: Tenebrionidae) larvae.

The spectrum of Tenebrio molitor larval digestive proteinases was studied in the context of the spatial organization of protein digestion in the midgut. The pH of midgut contents increased from 5.2-5.6 to 7.8-8.2 from the anterior to the posterior. This pH gradient was reflected in the pH optima of the total proteolytic activity, 5.2 in the anterior and 9.0 in the posterior midgut. When measured at the pH and reducing conditions characteristic of each midgut section, 64% of the total proteolytic activity was in the anterior and 36% in the posterior midgut. In the anterior midgut, two-thirds of the total activity was due to cysteine proteinases, whereas the rest was from serine proteinases. In contrast, most (76%) of the proteolytic activity in the posterior midgut was from serine proteinases. Cysteine proteinases from the anterior were represented by a group of anionic fractions with similar electrophoretic mobility. Trypsin-like activity was predominant in the posterior midgut and was due to one cationic and three anionic proteinases. Chymotrypsin-like proteinases also were prominent in the posterior midgut and consisted of one cationic and four anionic proteinases, four with an extended binding site. Latent proteinase activity was detected in each midgut section. These data support a complex system of protein digestion, and the correlation of proteinase activity and pH indicates a physiological mechanism of enzyme regulation in the gut.

[Protease inhibitors: use to increase plant tolerance to insects and pathogens].

The review deals with analysis of the possibility of the use of genes of inhibitors of proteolytic enzymes of plants to increase plant tolerance to insect pests and phytopathogens. The idea of using protease inhibitors for plant defense is strongly supported, first, by their wide distribution in plant tissues and high activity towards various proteolytic enzymes of insects, bacteria and fungi. The results obtained for the last years indicate that the genetic engineering approach is perspective for solving of this kind of problems. The main losses and advantages of the discussed approach are also considered. The described approach for increase of plant tolerance to insects and pathogens has few advantages as compared to traditional ones and belongs to ecologically pure technologies.

A chymotrypsin-like proteinase from the midgut of Tenebrio molitor larvae.

A chymotrypsin-like proteinase was isolated from the posterior midgut of larvae of the yellow mealworm, Tenebrio molitor, by ion-exchange and gel filtration chromatography. The enzyme, TmC1, was purified to homogeneity as determined by SDS-PAGE and postelectrophoretic activity detection. TmC1 had a molecular mass of 23.0 kDa, pI of 8.4, a pH optimum of 9.5, and the optimal temperature for activity was 51 degrees C. The proteinase displayed high stability at temperatures below 43 degrees C and in the pH range 6.5-11.2, which is inclusive of the pH of the posterior and middle midgut. The enzyme hydrolyzed long chymotrypsin peptide substrates SucAAPFpNA, SucAAPLpNA and GlpAALpNA and did not hydrolyze short chymotrypsin substrates. Kinetic parameters of the enzymatic reaction demonstrated that the best substrate was SucAAPFpNA, with k(cat app) 36.5 s(-1) and K(m) 1.59 mM. However, the enzyme had a lower K(m) for SucAAPLpNA, 0.5 mM. Phenylmethylsulfonyl fluoride (PMSF) was an effective inhibitor of TmC1, and the proteinase was not inhibited by either tosyl-l-phenylalanine chloromethyl ketone (TPCK) or N(alpha)-tosyl-l-lysine chloromethyl ketone (TLCK). However, the activity of TmC1 was reduced with sulfhydryl reagents. Several plant and insect proteinaceous proteinase inhibitors were active against the purified enzyme, the most effective being Kunitz soybean trypsin inhibitor (STI). The N-terminal sequence of the enzyme was IISGSAASKGQFPWQ, which was up to 67% similar to other insect chymotrypsin-like proteinases and 47% similar to mammalian chymotrypsin A. The amino acid composition of TmC1 differed significantly from previously isolated T. molitor enzymes.

Digestive proteinases of yellow mealworm (Tenebrio molitor) larvae: purification and characterization of a trypsin-like proteinase.

A new trypsin-like proteinase was purified to homogeneity from the posterior midgut of Tenebrio molitor larvae by ion-exchange chromatography on DEAE-Sephadex A-50 and gel filtration on Superdex-75. The isolated enzyme had molecular mass of 25.5 kD and pI 7.4. The enzyme was also characterized by temperature optimum at 55 degrees C, pH optimum at 8.5, and K(m) value of 0.04 mM (for hydrolysis of Bz-Arg-pNA). According to inhibitor analysis the enzyme is a trypsin-like serine proteinase stable within the pH range of 5.0-9.5. The enzyme hydrolyzes peptide bonds formed by Arg or Lys residues in the P1 position with a preference for relatively long peptide substrates. The N-terminal amino acid sequence, IVGGSSISISSVPXQIXLQY, shares 50-72% identity with other insect trypsin-like proteinases, and 44-50% identity to mammalian trypsins. The isolated enzyme is sensitive to inhibition by plant proteinase inhibitors and it can serve as a suitable target for control of digestion in this stored product pest.

Compartmentalization of proteinases and amylases in Nauphoeta cinerea midgut.

Compartmentalization of proteinases, amylases, and pH in the midgut of Nauphoeta cinerea Oliv. (Blattoptera:Blaberidae) was studied in order to understand the organization of protein and starch digestion. Total proteolytic activity measured with azocasein was maximal at pH 11.5 both in anterior (AM) and posterior (PM) halves of the midgut, but the bulk of activity (67%) was found in PM. Total AM and PM preparations were fractionated on a Sephadex G-50 column and further analysed by means of activity electrophoresis and specific inhibitors and activators. The major activity in PM was classified as an unusual SH-dependent proteinase with M(r) 24,000 and pH optimum with synthetic substrate BApNA at 10.0. The enzyme was 43-fold activated in the presence of 1 mM DTT, insensitive to synthetic inhibitors of serine (PMSF, TLCK, TPCK) and cysteine (IAA, E-64) proteinases, strongly inhibited by STI, and displayed four active bands on zymograms. In PM, activities of trypsin-like, chymotrypsin-like, subtilisin-like, and cysteine proteinases were observed. Aspartic and metalloproteinases were not detected. In AM, activity of unusual SH-dependent proteinase also dominated and activity of chymotrypsin-like proteinase was observed, but their levels were much lower than in PM. Distribution of amylase activity, exhibiting an optimum at pH 6.0, was quite the opposite. The major part of it (67%) was located in AM. Treatment of amylase preparation with proteinases from AM and PM reduced amylase activity twofold. pH of the midgut contents was 6.0-7.2 in AM, 6.4-7.6 in the first and 8.8-9.3 in the second halves of PM. Thus, pH in AM is in good agreement with the optimal pH of amylase, located in this compartment, but the activity of proteinases, including the ability to degrade amylase, in such an environment is low. Active proteolysis takes place in the second half of PM, where pH of the gut is close to the optimal pH of proteinases.

Proteinase inhibitors in Nauphoeta cinerea midgut.

Proteinase inhibitors were studied in the midgut of Nauphoeta cinerea Oliv. (Blattoptera: Blaberidae) in experimental conditions, excluding their nutritional origin. One trypsin inhibitor (TI) with M(r) 8,000 and two subtilisin inhibitors (SI1 and SI2) with M(r) 13,000 and 8,000 were detected after fractionation of total protein preparation on Sephadex G-50. Ninety-four percent of both types of inhibitors was located in anterior midgut (AM). TI was 120-fold purified by FPLC-chromatography on Mono Q. Its isoelectric point was 4.3. TI lost a large part of activity in acidic and especially in alkaline medium. TI, SI1, and SI2 effectively inhibited activities of endogenous proteinases from posterior midgut (PM) of the cockroach. A search for inhibitor of endogenous unusual SH-dependent proteinase from AM revealed in AM a new inhibitor with M(r) 18,000. It was also inactivated in alkaline medium and was effective against proteinases from PM along with unusual SH-dependent proteinase from AM. A mechanism of regulation of activity of midgut proteinases is proposed based on pH-stability of inhibitors.

Localization of a metalloproteinase and its inhibitor in the protein bodies of buckwheat seeds.

Cotyledons of dry buckwheat (Fagopyrum esculentum Moench) seeds were used to study the cellular localization of a metalloproteinase which performs in vitro the initial limited proteolysis of the main storage protein of the seed, and of its proteinaceous inhibitor. Fractions of complex protein bodies (PB 1) and of the cytoplasm and membrane material (CMM) were obtained by fractionating cotyledons in a mixture of acetone and CCl4. The greater part of the metalloproteinase activity was found to be localized in the PB 1 fraction, with a lesser amount in the CMM fraction, whereas the metalloproteinase inhibitor was localized almost entirely in the PB 1 fraction. The data obtained indicate that the complex protein bodies of dry buckwheat seeds contain the components of the proteolytic system responsible for the initial degradation of the main storage protein - the 13S globulin - of buckwheat seeds, i.e. 13S globulin, the metalloproteinase, and its inhibitor. This confirms that it is possibile for the metalloproteinase to perform a controlled proteolysis of the 13S globulin in vivo. The effect of divalent cations on the degradation of the 13S globulin was also studied. A mechanism is discussed whereby the proteolysis of 13S globulin is initiated by divalent cations released as a result of phytin decationization during seedling growth.

[Isolation of histones from the nuclei of the flagellatum Astasia longa]. / Vydelenie gistonov iz iader prosteishego astasio longa.

A new procedure for isolation of purified nuclear fraction from the cells of the phytoflagellatum Astasia longa has been developed. The resulting preparations were characterized in terms of their chemical composition. A method of isolation to total histone preparations from the nuclear fractions of A. longa based on the metabolic peculiarities of the phytoflagellatum has been developed. Pure histone fractions were obtained by intensive disruption and thorough washing of the nuclear fraction from the non-histone proteins with weak solutions of salts. The intensive proteolysis of the histones in the course of washing was stopped by an addition of the specific inhibitors of proteinases--phenylmethylsulfanylfluoride and pCMB (pH 7,8--8,0). The use of NaHSO3 or boiling of the nuclear fraction to suppress the histone proteolysis were found to be ineffective. Extraction of the histones by 1 M CaCl2 appeared more productive than the use of mineral acids solutions. The total histone preparation isolated under optimal conditions was found in the chromatin in amounts equivalent to those of DNA; its amino acid composition was typical for histones. During polyacrylamide gel electrophoresis in an acidic system in the presence of urea the histones produced four main bands, whereas in the presence of DS-Na--five bands. In terms of the amino acid composition and electrophoretic properties in different systems the histones of A. longa are similar but not identical to calf thymus histones.

[Histones from Trypanosoma lewisi nuclei]. / Gistony iader zhgutikovogo prosteishego Trypanosoma Lewisi.

A preparation of total histones has been isolated for the first time from the purified fractions of T. lewisi cell nuclei and characterized in terms of its chemical composition and RNA-polymerase activity. A special attention during the isolation procedure was given to the repression of proteolytic degradation of the histones. The amount of protein in the chromatin is equivalent to that of DNA. The amino acid composition and heterogeneity of the protein during polyacrylamide gel electrophoresis in an acid system and in the presence of sodium dodecyl sulfate are typical for histones. Using two-dimensional electrophoresis, differential staining of electrophoregrams and ion-exchange chromatography on CM-cellulose the total preparation has been found to be made up of five fractions: two -- arginine-rich (one of them identical to histone H4, the other being similar to histone H3 from calf thymus); two -- moderately lysine-rich fractions, slightly differing in their properties from histones H2A and H2B from calf thymus, and one specific fraction with mol. weight of 16 000 and an extremely high positive charge. The above methods in combination with specific extraction have been used to demonstrate the absence of a typical lysine histone in the preparation, which is correlated with the absence of typical methaphase chromosomes during mitosis in T. lewisi.