Unusual features of a recombinant apple α-farnesene synthase

Abstract

A recombinant α-farnesene synthase from apple ( Malus × domestica), expressed in Escherichia coli, showed features not previously reported. Activity was enhanced 5-fold by K + and all four isomers of α-farnesene, as well as β-farnesene, were produced from an isomeric mixture of farnesyl diphosphate (FDP). Monoterpenes, linalool, ( Z)- and ( E)-β-ocimene and β-myrcene, were synthesised from geranyl diphosphate (GDP), but at 18% of the optimised rate for α-farnesene synthesis from FDP. Addition of K + reduced monoterpene synthase activity. The enzyme also produced α-farnesene by a reaction involving coupling of GDP and isoprenyl diphosphate but at <1% of the rate with FDP. Mutagenesis of active site aspartate residues removed sesquiterpene, monoterpene and prenyltransferase activities suggesting catalysis through the same active site. Phylogenetic analysis clusters this enzyme with isoprene synthases rather than with other sesquiterpene synthases, suggesting that it has evolved differently from other plant sesquiterpene synthases. This is the first demonstration of a sesquiterpene synthase possessing prenyltransferase activity.