کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1982423 1062286 2011 12 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Insecticidal effect of Canavalia ensiformis major urease on nymphs of the milkweed bug Oncopeltus fasciatus and characterization of digestive peptidases
موضوعات مرتبط
علوم زیستی و بیوفناوری علوم کشاورزی و بیولوژیک دانش حشره شناسی
پیش نمایش صفحه اول مقاله
Insecticidal effect of Canavalia ensiformis major urease on nymphs of the milkweed bug Oncopeltus fasciatus and characterization of digestive peptidases
چکیده انگلیسی

Jackbean (Canavalia ensiformis) ureases are entomotoxic upon the release of internal peptides by insect’s digestive enzymes. Here we studied the digestive peptidases of Oncopeltus fasciatus (milkweed bug) and its susceptibility to jackbean urease (JBU). O. fasciatus nymphs fed urease showed a mortality rate higher than 80% after two weeks. Homogenates of midguts dissected from fourth instars were used to perform proteolytic activity assays. The homogenates hydrolyzed JBU in vitro, yielding a fragment similar in size to known entomotoxic peptides. The major proteolytic activity at pH 4.0 upon protein substrates was blocked by specific inhibitors of aspartic and cysteine peptidases, but not significantly affected by inhibitors of metallopeptidases or serine peptidases. The optimal activity upon N-Cbz-Phe-Arg-MCA was at pH 5.0, with complete blockage by E-64 in all pH tested. Optimal activity upon Abz–AIAFFSRQ–EDDnp (a substrate for aspartic peptidases) was detected at pH 5.0, with partial inhibition by Pepstatin A in the pH range 2–8. Fluorogenic substrates corresponding to the N- and C-terminal regions flanking a known entomotoxic peptide within urease sequence were also tested. While the midgut homogenate did not hydrolyze the N-terminal peptide, it cleaved the C-terminal peptide maximally at pH 4.0–5.0, and this activity was inhibited by E-64 (10 μM). The midgut homogenate was submitted to ion-exchange chromatography followed by gel filtration. A 22 kDa active fraction was obtained, resolved in SDS-PAGE (12%), the corresponding band was in-gel digested by trypsin, the peptides were analyzed by mass spectrometry, retrieving a cathepsin L protein. The purified cathepsin L was shown to have at least two possible cleavage sites within the urease sequence, and might be able to release a known insecticidal peptide in a single or cascade event. The results suggest that susceptibility of O. fasciatus nymphs to jackbean urease is, like in other insect models, due mostly to limited proteolysis of ingested protein and subsequent release of entomotoxic peptide(s) by cathepsin-like digestive enzymes.

Figure optionsDownload high-quality image (104 K)Download as PowerPoint slideHighlights
► Jackbean urease fed to milkweed bug Oncopeltus fasciatus produces 100% mortality.
► Insect digestive enzyme(s) release(s) insecticidal peptide(s) from jackbean urease.
► Soluble aspartic and cysteine proteases predominate in Oncopeltus fasciatus midgut.
► Soluble serine and metalloproteases are minoritary in Oncopeltus fasciatus midgut.
► Oncopeltus fasciatus midgut cathepsin L (22 kDa) cleaves Ile–Arg bonds.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Insect Biochemistry and Molecular Biology - Volume 41, Issue 6, June 2011, Pages 388–399
نویسندگان
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