Identification of a product specific b-amyrin synthase from Arabidopsis thaliana

Triterpene skeletons are produced by oxidosqualene cyclases (OSCs). The genome sequencing of Arabidopsis thaliana revealed the presence of thirteen OSC homologous genes including At1g78950, which has been revised recently as two independent ORFs, namely At1g78950 and At1g78955. The cDNA corresponding to the revised At1g78950 was obtained by RT-PCR, ligated into Saccharomyces cerevisiae expression vector pYES2, and expressed in a lanosterol synthase deficient S. cerevisiae strain. LC-MS and NMR analyses of the accumulated product in the host cells showed that the product of At1g78950 is b-amyrin, indicating that At1g78950 encodes a b-amyrin synthase (EC 5.4.99.-).