Inhibitor binding insect

Because suicide inhibitors bind to the active site, the can be used to find what amino acids are present there. Malathion and other organophosphates are suicide inhibitors of insect AChE, so are widely used as insecticides. 

The mechanisms of resistance fall into two main categories. Many insects produce an increased level of detoxifying enzymes, such as esterases, that modify the insecticides to inactive metabolites very rapidly. Such a system is seen in aphids that are resistant to OP insecticides. In other cases it is the target site that is modified such that the insecticide (the enzyme inhibitor) no longer binds to the target and is, therefore, ineffective. This has recently been shown to occur in some aphids that are resistant to OP insecticides but the classical example is knockdown resistance (kdr) and super-kdr to pyrethroid insecticides shown by many insects but particularly house flies Musca domes tied). This resistance is thought to result from a modification of... 

One of the hallmarks of OBPs is the six cysteine (six half cystines) residues, but this criterion alone is not sufficient to classify a certain protein as olfactory protein. It is important to demonstrate that an OBP is expressed only (or predominantly) in olfactory tissues. Evidence for their ability to bind odorants is also desirable, but not sine qua non. One of these criteria alone would not be enough to define a given protein as an OBP. For example, bovine serum albumin (BSA) binds to insect pheromones (Leal, unpublished data) and yet it is not an OBP because it does not occur in olfactory tissues in the first place. Conversely, a protein specific to antennae is not necessarily an OBP. There are other proteins that may be expressed in antennae but not in control tissues. Non-OBPs specific to insect antennae have been previously detected (Ishida and Leal, unpublished data). Also, a g lu tath i o n e -. S -1 ra n s I e ra s e has been reported to be expressed specifically in antennae of M. sexta (Rogers et al., 1999). Likewise, the six-cysteine criterion should not be misleadingly used. Insulin and bovine pancreatic trypsin inhibitor, for example, have six cysteines in three disulfide bridges and yet they are not odorant-binding proteins. Also, mammalian and insect defensins have six well-conserved cysteine residues. 

P-gp associated ATPase is vanadate sensitive. A membrane product prepared from baculovirus infected insect cells containing this activity is now commercially available from Gentest Corp. (Woburn, Massachusetts, U.S.). Substrates of P-gp, such as verapamil, have been demonstrated to stimulate this vanadate-sensitive membrane ATPase (123). By determination of inorganic phosphate liberated in the reaction containing a P-gp preparation and a test compound, in the presence and absence of vanadate, one can determine if the test compound is a substrate/inhibitor of P-gp (123,422). Any compound that binds to P-gp would stimulate the magnesium-dependent ATPase, and thus, this method cannot distinguish between a substrate and inhibitor of P-gp. 

Organophosphate insecticides with the P=S group are oxidatively desulfurated by cytochrome P450 monooxygenases of insects to their corresponding P=0 analogs. This reaction results in activation (increased toxicity), because the product, P=0, binds more tightly to the acetylcholinesterase than the parent compound and, thus, to more potent acetylcholinesterase inhibitors. For example, parathion is oxidatively desulfurated to paraoxon. 

Proteolytic activation of Cry toxins is critical not only for protoxin activation, but has also implications for toxin specificity [59,60], receptor binding [61], and insect resistance [62,63]. The absence of a major gut protease in Plodia interpmctdla correlated with its resistance to Cry 1 Ac [62]. Moreover, rapid degradation of Cry toxins was associated with the loss of sensitivity of S instar 5. litoralis larvae to Cry 1C [64], and serine protease inhibitors enhanced the toxicity of some Cry proteins up to 20-fold [65]. 

Roussel A, et al. Complexation of two proteic insect inhibitors to the active site of chymotrypsin suggests decoupled roles for binding and selectivity. J. Biol. Chem. 2001 276 38893-38898. 

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