Identification of a Fungal 1,8-cineole Synthase from Hypoxylon sp. with Common Specificity Determinants to the Plant Synthases [Enzymology]

February 3rd, 2015 by Shaw, J. J., Berbasova, T., Sasaki, T., Jefferson-George, K., Spakowicz, D. J., Dunican, B. F., Portero, C. E., Narvaez-Trujillo, A., Strobel, S. A.

Terpenes are an important and diverse class of secondary metabolites widely produced by fungi. Volatile compound screening of a fungal endophyte collection revealed a number of isolates in the family Xylariaceae, producing a series of terpene molecules including 1,8-cineole. This compound is a commercially important component of eucalyptus oil used in pharmaceutical applications and has been explored as a potential biofuel additive. The genes that produce terpene molecules such as 1,8-cineole have been little explored in fungi, providing an opportunity to explore the biosynthetic origin of these compounds. Through genome sequencing of cineole producing isolate E7406B we were able to identify eleven new terpene synthase genes. Expressing a subset of these genes in E. coli allowed identification of the hyp3 gene, responsible for 1,8-cineole biosynthesis, the first monoterpene synthase discovered in fungi. In a striking example of convergent evolution, mutational analysis of this terpene synthase revealed an active site asparagine critical for water capture and specificity during cineole synthesis, the same mechanism used in an unrelated plant homologue. These studies have provided insight into the evolutionary relationship of fungal terpene synthases to those in plants and bacteria, and further established fungi as a relatively untapped source of this important and diverse class of compounds.