Cyanogenic glycosides: a case study for evolution and application of cytochromes P450

Abstract

Cyanogenic glycosides are ancient biomolecules found in more than 2,650 higher plant species as well as in a few arthropod species. Cyanogenic glycosides are amino acid-derived β-glycosides of α-hydroxynitriles. In analogy to cyanogenic plants, cyanogenic arthropods may use cyanogenic glycosides as defence compounds. Many of these arthropod species have been shown to de novo synthesize cyanogenic glycosides by biochemical pathways that involve identical intermediates to those known from plants, while the ability to sequester cyanogenic glycosides appears to be restricted to Lepidopteran species. In plants, two atypical multifunctional cytochromes P450 and a soluble family 1 glycosyltransferase form a metabolon to facilitate channelling of the otherwise toxic and reactive intermediates to the end product in the pathway, the cyanogenic glycoside. The glucosinolate pathway present in Brassicales and the pathway for cyanoalk(en)yl glucoside synthesis such as rhodiocyanosides A and D in Lotus japonicus exemplify how cytochromes P450 in the course of evolution may be recruited for novel pathways. The use of metabolic engineering using cytochromes P450 involved in biosynthesis of cyanogenic glycosides allows for the generation of acyanogenic cassava plants or cyanogenic Arabidopsis thaliana plants as well as L. japonicus and A. thaliana plants with altered cyanogenic, cyanoalkenyl or glucosinolate profiles.