Identification and Characterisation of Gut Proteases in the Fig Tree Skeletoniser Moth, Choreutis Nemorana Hübner (Lepidoptera: Choreutidae)
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Plant Protect. Sci. Vol. 49, 2013, No. 1: 19–26 Identification and Characterisation of Gut Proteases in the Fig Tree Skeletoniser Moth, Choreutis nemorana Hübner (Lepidoptera: Choreutidae) Moloud GHOLAMZADEH CHITGAR, Mohammad GHADAMYARI and Mahbobe SHARIFI Department of Plant Protection, Faculty of Agricultural Science, University of Guilan, Rasht, Iran Abstract Gholamzadeh Chitgar M., Ghadamyari M., Sharifi M. (2013): Identification and characterisation of gut proteases in the fig tree skeletoniser moth, Choreutis nemorana Hübner (Lepidoptera: Choreutidae). Plant Protect. Sci., 49: 19–26. The biochemical properties of proteases from the digestive system of the fig tree skeletonizer moth, Choreutis nemo- rana, were determined. Gut extracts of C. nemorana larvae were analysed using different specific peptide substrates and proteinase inhibitors. The optimal pH and temperature for proteolytic activities using azocasein as substrate were obtained as pH 11 and 45°C, respectively. In the case of N-benzoyl-l-arg-p-nitroanilide as substrate, the enzyme showed the maximum tryptic activity at pH 11. The kinetic parameters of trypsin-like proteases indicated that the Km and Vmax values of trypsin in the gut of C. nemorana were 0.157 ± 0.006mM and 0.188 ± 0.005 µmol/min/mg pro- tein. Using specific proteolytic inhibitors, the inhibitors including phenyl methane sulfonyl fluoride, N-p-tosyl-l-lys chloromethyl ketone and ethylene diamine tetraacetic acid showed the greatest inhibitory effect on total proteolytic activity. These results indicated that serine proteinases accounted for the major proteases in the gut of C. nemorana. Inhibition assays and zymogram analysis showed that only small amounts of cysteine proteases are present in the digestive system of C. nemorana. Keywords: protease inhibitors; fig leaf roller moth; gut; trypsin; chymotrypsin Insects need an adequate source of protein in interfere with food digestion in the insect gut order to grow and maintain themselves. Proteins sufficiently to control them. Transgenic plants comprised in amino acids and these organic com- expressing protease inhibitors can kill the pest. pounds are fundamental for growth, reproduction, These inhibitors can bind with dominant digestive and as a structural element of the cell in the insect proteases of insects feeding on the host plants, body. Proteases are very important enzymes in impairing their digestion and retarding growth the alimentary canal of insects and they cleave and larval development in some insect species the peptide bonds in the proteinous insect foods including lepidoptera (Gatehouse et al. 2000). to release the amino acids that are then absorbed Serine proteases and metallo-exopeptidase are by epithelial cells of the insect midgut. Proteoly- dominant active proteases in the digestive system sis plays an important role in insect physiology of lepidopteran larvae (Patankar et al. 2001; and food digestion, facilitated by serine, cysteine, Josephrajkumar et al. 2006; Chougule et al. aspartic proteinases or endopeptidases and metal- 2008). Also, serine proteases have been reported loproteinases. It is very important to study insect from the digestive tracts of many insects belong proteases due to disorders of protein digestion in to different orders and families and these enzymes the digestive tract of insects by protease inhibitors are inhibited by serine protease inhibitors available (Josephrajkumar et al. 2006). Protease inhibi- in legume and cereal plants. Also, serine protease tors are proteins or small polypeptides that may inhibitors have been found in some plants and Supported by the Research Council of the University of Guilan, Grant No. K2937. 19 Vol. 49, 2013, No. 1: 19–26 Plant Protect. Sci. showed insecticidal effects on several lepidopteran tors can reduce the nutritional quality of food for larvae (Ussuf et al. 2001). C. nemorana. The first step for discovering the The fig tree skeletonizer moth, Choreutis nemo- protease inhibitors is identification and biochemi- rana Hübner (Lepidoptera: Choreutidae), is a gen- cal characterisation of digestive proteases in the erally common pest of fig trees in Guilan province, insect gut. Characterisation and identification of Iran. The larvae of this pest feed on leaves of the the type of digestive proteases is fundamental to fig tree causing massive defoliation but, at times studying nutritional physiology and degradation or of severe infestation, it also feeds on developing activation of toxin protein such as Bt delta endo- leaves resulting in a huge loss of the crop. They toxin (Knop Wrigth et al. 2006). Therefore, this are protected by a web of silken threads and feed paper reports biochemical properties of digestive on upper epidermal and parenchyma cells (Al- proteases of C. nemorana. Also, we studied the ford 2007) and penetration of pesticides to this effects of various inhibitors on enzyme activities protected area is considered to be hindered. Di- with the aim of identification and application of azinon and chlorpyriphos were recommended as new pest management technologies. foliar insecticides against this pest by the Iranian Plant Protection Organization (IPPO). Also, the extensive and exclusive use of chemical pesticides MATERIAL AND METHODS may result in pollution and developing of resist- ance to such compounds and impair the balance Chemicals. Azocasein, BApNA (N-benzoyl-l- between pests and natural enemies (Metcalf arginine-p-nitroanilide), BTEE (benzoyl-l-tyrosine 1986). Heavy reliance on chemical methods is ethyl ester), TLCK (N-p-tosyl-l-lysine chlorome- highly unsafe. Therefore, development of alterna- thyl ketone), TPCK (N-tosyl-l-phenylamine chlo- tive or safe methods instead of the chemical control romethyl ketone), PMSF (phenyl methane sulfonyl such as the use of transgenic plants expressing fluoride), iodoacetate were purchased from Sigma proteinase and carbohydrase inhibitors is highly (St. Louis, USA). Trichloroacetic acid and EDTA advisable. Protease inhibitors are among the plant (ethylene diamine tetraacetic acid) were obtained defence mechanisms against herbivorous pests. from Merck Company (Darmstadt, Germany). These proteins can inhibit proteases present in Insects. C. nemorana larvae were collected from insect midguts or produced by symbionts, lead fig trees in Rasht, Iran. This population has been to a reduction in absorbable amino acids which maintained on fig leaves in optimum rearing condi- are necessary for insect growth, reproduction tions of 25 ± 2°C, 60 ± 10% RH with a photoperiod and survival (Volpicella et al. 2003). Addition- of 16 h light and 8 h dark. ally, protease inhibitors from various plants have Enzyme preparation. Last-larval instars were been used against different mechanistic classes of selected for gut extraction. The individuals were proteases in order to control pests for a long time. chilled and dissected on ice. The whole gut with Their use in the insect control is notable based lumen contents was used. The digestive system on several studies indicating their effectiveness in of ten individuals was used as one sample. Each disruption of protease digestion. The lepidopteran sample was replicated at least 3 times and 3 samples larvae use a complex proteolytic enzymes including were used for each measurement. The collected trypsins, chymotrypsins, elastases, cathepsin-B like guts were then homogenized in a known volume of proteases, aminopeptidases, and carboxypeptidases distilled water using plastic pestles, centrifuged at for protein digestion and many serine proteases 10 000× g and 4°C for 10 minutes. The supernatant are dominant in the larval gut (Patankar et al. was used as an enzyme solution. 2001; Srinivasan et al. 2006; Chougule et al. Determination of general protease activity. 2008; Tabatabaei et al. 2011). Insect digestive Total proteolytic activity of gut enzyme extracts was proteases have different biochemical properties. evaluated using the proteinase substrate azocasein Therefore, our knowledge of the properties of 2.5%. The reaction mixture consisted of 15 µl of midgut digestive protease is necessary for develop- enzyme and 43 µl of 50mM sodium acetate-phos- ing rational control strategy based on transgenic phate-glycine buffer with the desired pH (pH = 11). plants expressing inhibitors (Wilhite et al. 2000). After 5 min, 17 µl of the substrate azocasein was Protease inhibitors can be regarded as the best added and the reaction mixture was incubated choice method against this insect and these inhibi- at 35°C for 90 minutes. Then, the reaction was 20 Plant Protect. Sci. Vol. 49, 2013, No. 1: 19–26 stopped by adding 50 µl of 30% trichloroacetic acid Kinetic parameters of trypsin. The Michaelis- (TCA) and then rested at 4°C for 30 minutes. Then Menten constant (Km) and the maximal reaction all samples were centrifuged at 13 000 rpm and velocities (Vmax) of trypsin were determined by 4°C for 10 minutes. 100 µl of the supernatant was Lineweaver-Burk plots. The measurements were then transferred to the microplate well and added carried out at pH 11.0, measuring the initial rates of an equal volume of 1N NaOH before the absorb- reaction with increasing substrate concentrations. ance was read. The absorbance was measured at BApNA was used as substrate at a final concen- ® 440 nm (with a microplate reader Stat Fax 3200 tration range of 0.0156 to 1mM. The experiments (Awareness Technology Inc., Palm City, USA) and were performed in triplicate (Sharifi et al. 2012b) then converted to units of protease activity