Evolutionary, Functional and Mechanistic Characterisation of Microbial Terpene Synthase-Like Genes From Springtails

Despite previous doubts about the origin of terpenes in springtails, a deep bioinformatic analysis of the genomes of 26 springtails surprisingly revealed the presence of many genes coding for microbial-type terpene synthases. Five candidate enzymes from Sinella curviseta representing different branches of a phylogenetic tree were selected for investigation, four of which were active in in vitro incubations with an enzyme-dependent substrate selectivity ranging from farnesyl (FPP) to geranylfarnesyl pyrophosphate (GFPP), with formation of multiple products in all cases. The obtained enzyme products included the new macrocycle sestersinellene, the enantiomer of a sesterterpene produced by a terpene synthase from Leucosceptrum canum and the unusual diterpene sinellene ether representing a novel skeleton, reinforcing springtails as an interesting source of terpenes. Extensive isotopic labelling experiments revealed several unusual mechanistic aspects such as the formation of a series of enantiomerically pure products besides one scalemic compound (germacrene D), as well as an unexpected stereochemical course for a reprotonation step in sinellene ether biosynthesis by ScTC2. Taken together, this study lays the foundation for future research on terpene biosynthesis in Collembola, an ancient lineage of arthropods.