アイテム詳細

要旨

Cyanogenic glucosides are widespread defence compounds in plants, and they are also found in some arthropods, especially
within Lepidoptera. The aliphatic linamarin and lotaustralin are the most common cyanogenic glucosides in Lepidoptera, and
they are biosynthesised de novo, and/or sequestered from food plants. Their biosynthetic pathway was elucidated in the burnet
moth, Zygaena filipendulae, and consists of three enzymes: two cytochrome P450 enzymes, CYP405A2 and CYP332A3, and
a glucosyl transferase, UGT33A1. Heliconius butterflies also produce linamarin and lotaustralin and have close homologs to
CYP405A2 and CYP332A3. To unravel the evolution of the pathway in Lepidoptera, we performed phylogenetic analyses on
all available CYP405 and CYP332 sequences. CYP332 sequences were present in almost all Lepidoptera, while the distribution
of CYP405s among butterflies and moths was much more limited. Negative purifying selection was found in both CYP
enzyme families, indicating that the biosynthesis of CNglcs is an old trait, and not a newly evolved pathway. We compared
CYP405A2 to its close paralog, CYP405A3, which is not involved in the biosynthetic pathway. The only significant difference
between these two enzymes is a smaller substrate binding pocket in CYP405A2, which would make the enzyme more
substrate specific. We consider it likely that the biosynthetic pathway of CNglcs in butterflies and moths have evolved from
a common pathway, perhaps based on a predisposition for detoxifying aldoximes by way of a CYP332. Later the aldoxime
metabolising CYP405s evolved, and a UGT was recruited into the pathway to establish de novo biosynthesis of CNglcs.