Chemical Communication in a Post-Genomic World (2003) / Chapter Skim
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16 Diversification of furanocoumarin-metabolizing cytochrome P450 monooxygenases in two papilionids: Specificity and substrate encounter rate
16 Diversification of furanocoumarin-metabolizing cytochrome P450 monooxygenases in two papilionids: Specificity and substrate encounter rate
Pages 81-86
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From page 81... ...
These P450s in turn catalyze a larger range of furanocoumarins at lower efficiency than CYP6B1, a P450 from Papi/io polyxenes, which feeds exclusively on furanocoumarin-containing host plants. Reconstruction of the ancestral CYP6B sequences using maximum likelihood predictions and comparisons of the sequence and geometry of their active sites to those of contemporary CYP6B proteins indicate that host plant diversity is directly related to P450 activity and inversely related to substrate specificity.
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From page 82... ...
species, Papilio glaucus, which occasionally encounters furanocoumarins, and Papilio canadensis, which is unlikely to encounter furanocoumarins because of the absence of furanocoumarins in its available host plants, also have inducible metabolisms of furanocoumarins (16~. Sixteen highly conserved genes (92-99% protein identity)
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From page 83... ...
with the implementation of Jones amino acid transformation model and iteratively estimated fly shape parameter. To subsequently determine the relationship of ancestral sequences to their descendant P450s, relative amino acid distances between the ancestral sequences and their descendant branches were computed by using the MEGA program based on either complete protein sequences or active site amino acid residues.
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From page 84... ...
CYP6B7, CYP6B8, and CYP6B27, which are derived from Helicoverpa zea/Helicoverpa armigera, two closely related agricultural pests with extremely wide host ranges, are inducible by a wide range of chemicals, including insecticides, plant hormones, and plant allelochemicals, such as xanthotoxin (28-30~. Among these, the CYP6B8 protein has a demonstrated ability to metabolize a range of plant allelochemicals and insecticides (31)
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From page 85... ...
Grouped bars representthe ratio of average amino acid distance between ancestral sequence and the upper branch to that of the lower branch. The distance ratio was computed either based on active site residues (filled bars)
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From page 86... ...
It is highly likely that insects possessing CYP6B enzymes originated from a broadly polyphagous species with limited capacity for specialized metabolism. As the specialist papilionids diverged from this generalist ancestor in association with their furanocoumarin-containing host plants, the ability to metabolize a broad range of substrates declined as the ability to metabolize the principal host plant defense compounds, the furanocoumarins, reached a level of refinement rarely equaled by other herbivores.
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