Diversity in digestive proteinase activity among insects

Wolfson, Jane L.; Murdock, Larry L.

doi:10.1007/bf01021013

Cited by 128 publications

(75 citation statements)

References 4 publications

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“…2 and Table 1). Protease inhibitors were used at a concentration known to be largely sufficient to inhibit the type of protease against which they are active (5,51,58,65). Because in theory protease inhibitors could either stimulate or inhibit pore formation, a toxin concentration of 50 pmol toxin/mg of membrane protein was chosen to test all inhibitors.…”

Section: Resultsmentioning

confidence: 99%

Protease Inhibitors Fail To Prevent Pore Formation by the Activated Bacillus thuringiensis Toxin Cry1Aa in Insect Brush Border Membrane Vesicles

Kirouac

Vachon

Quievy

et al. 2006

Appl Environ Microbiol

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To investigate whether membrane proteases are involved in the activity of Bacillus thuringiensis insecticidal toxins, the rate of pore formation by trypsin-activated Cry1Aa was monitored in the presence of a variety of protease inhibitors with Manduca sexta midgut brush border membrane vesicles and by a light-scattering assay. Most of the inhibitors tested had no effect on the pore-forming ability of the toxin. However, phenylmethylsulfonyl fluoride, a serine protease inhibitor, promoted pore formation, although this stimulation only occurred at higher inhibitor concentrations than those commonly used to inhibit proteases. Among the metalloprotease inhibitors, o-phenanthroline had no significant effect; EDTA and EGTA reduced the rate of pore formation at pH 10.5, but only EDTA was inhibitory at pH 7.5. Neither chelator affected the properties of the pores already formed after incubation of the vesicles with the toxin. Taken together, these results indicate that, once activated, Cry1Aa is completely functional and does not require further proteolysis. The effect of EDTA and EGTA is probably better explained by their ability to chelate divalent cations that could be necessary for the stability of the toxin's receptors or involved elsewhere in the mechanism of pore formation.Bacillus thuringiensis is by far the most widely used alternative to chemical insecticides for the control of insect pests in forestry, agriculture, and public health. During sporulation, this bacterium produces insecticidal proteins that accumulate in the form of parasporal crystals. Following their ingestion by susceptible insect larvae, these protoxins are solubilized and converted to active toxins by midgut proteases. Activated toxins act by forming pores after binding to specific receptors at the surface of the insect midgut luminal membrane, leading to cell lysis, destruction of the epithelium, and death of the insect (52). In their activated form, all B. thuringiensis Cry toxins for which the crystal structure has been solved share a similar three-domain structure (7,21,24,33,34,44). Domain I is composed of a bundle of seven anti-parallel ␣-helices and is generally thought to be responsible for membrane insertion and pore formation, while domains II and III are mainly composed of ␤-sheets and involved in the binding, specificity, and stability of the toxin (24, 33, 52).Midgut proteases play an essential role in the activation of B. thuringiensis toxins (1, 6, 13). In the case of Cry1A toxins, the first 28 amino acid residues are removed from the N terminus and approximately half of the protoxin residues are removed from the C terminus (6). However, susceptibility of the activated toxins to further proteolysis in the midgut environment could possibly affect toxicity and explain apparent discrepancies that are occasionally observed between their in vitro and in vivo activities (15,41,49,60). For example, Cry1Ca can be completely degraded when incubated with midgut juice from advanced larval instars of Spodoptera littoralis (29). Synergisti...

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Section: Resultsmentioning

confidence: 99%

Protease Inhibitors Fail To Prevent Pore Formation by the Activated Bacillus thuringiensis Toxin Cry1Aa in Insect Brush Border Membrane Vesicles

Kirouac

Vachon

Quievy

et al. 2006

Appl Environ Microbiol

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“…Coleopteran and hemipteran species tend to utilize cysteine proteinases ) while lepidopteran, hymenopteran, orthopteran and dipteran species mainly use serine proteinases (Ryan, 1990;Wolfson and Murdock, 1990). Examples from both of these classes of proteinases have been shown to be inhibited by their cognate proregions .…”

Section: Mechanism Of Toxicitymentioning

confidence: 99%

Plant protease inhibitors in control of phytophagous insects

Lawrence¹,

Koundal²

2002

Electron. J. Biotechnol.

290

178

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“…However, no significant differences in the pH of intestinal contents between populations or diet treatments were observed. Vertebrates may be limited in their ability to increase gut pH as a defense against PSCs, as their digestive enzymes usually operate optimally within pH ranges of 6 to 7.5 (Blair and Tuba, 1963;Maze and Gray, 1980), whereas some insect digestive enzymes can perform optimally up to a pH of 12 (Wolfson and Murdock, 1990). However, it is noteworthy that the intestinal pH of N. bryanti (~7.9) is far higher than that found in laboratory rodents (pH5-6) (McConnell et al, 2008).…”

Section: Discussionmentioning

confidence: 62%

Induced and constitutive responses of digestive enzymes to plant toxins in an herbivorous mammal

Kohl

Dearing

2011

Journal of Experimental Biology

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SUMMARYMany plants produce plant secondary compounds (PSCs) that bind and inhibit the digestive enzymes of herbivores, thus limiting digestibility for the herbivore. Herbivorous insects employ several physiological responses to overcome the anti-nutritive effects of PSCs. However, studies in vertebrates have not shown such responses, perhaps stemming from the fact that previously studied vertebrates were not herbivorous. The responses of the digestive system to dietary PSCs in populations of Bryantʼs woodrat (Neotoma bryanti) that vary in their ecological and evolutionary experience with the PSCs in creosote bush (Larrea tridentata) were compared. Individuals from naïve and experienced populations were fed diets with and without added creosote resin. Animals fed diets with creosote resin had higher activities of pancreatic amylase, as well as luminal amylase and chymotrypsin, regardless of prior experience with creosote. The experienced population showed constitutively higher activities of intestinal maltase and sucrase. Additionally, the naïve population produced an aminopeptidase-N enzyme that was less inhibited by creosote resin when feeding on the creosote resin diet, whereas the experienced population constitutively expressed this form of aminopeptidase-N. Thus, the digestive system of an herbivorous vertebrate responds significantly to dietary PSCs, which may be important for allowing herbivorous vertebrates to feed on PSC-rich diets. Supplementary material available online at

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Diversity in digestive proteinase activity among insects

Cited by 128 publications

References 4 publications

Protease Inhibitors Fail To Prevent Pore Formation by the Activated Bacillus thuringiensis Toxin Cry1Aa in Insect Brush Border Membrane Vesicles

Protease Inhibitors Fail To Prevent Pore Formation by the Activated Bacillus thuringiensis Toxin Cry1Aa in Insect Brush Border Membrane Vesicles

Plant protease inhibitors in control of phytophagous insects

Induced and constitutive responses of digestive enzymes to plant toxins in an herbivorous mammal

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