?-Amyrin synthase from Conyza blinii expressed in Saccharomyces cerevisiae.

ABSTRACT: Conyza blinii H.Lév. is a widely used medicinal herb in southwestern China. The main pharmacological components of C. blinii are a class of oleanane-type pentacyclic triterpene glycosides known as conyzasaponins, which are thought to be synthesized from ?-amyrin. However, no genes involved in the conyzasaponin pathway have previously been identified. Here, we identify an oxidosqualene cyclase (OSC), a ?-amyrin synthase, which mediates cyclization of 2,3-oxidosqualene to yield ?-amyrin. Ten OSC sequences were isolated from C. blinii transcript tags. Phylogenetic analysis was used to select the tag Cb18076 as the putative ?-amyrin synthase, named Cb?AS. The open reading frame of Cb?AS is 2286 bp and encodes 761 amino acids. Its mature protein contains the highly conserved motifs (QXXXGXW/DCTAE) of OSCs and (MWCYCR) of ?-amyrin synthases. Transcription of Cb?AS was upregulated 4-24 h after treatment of the seedlings of the C. blinii cultivar with methyl jasmonate. Furthermore, expression of Cb?AS in Saccharomyces cerevisiae successfully yielded ?-amyrin. The chemical structures and concentrations of ?-amyrin were confirmed by GC-MS/MS. The target yeast ultimately produced 4.432 mg·L-1 ?-amyrin. Thus, Cb?AS is an OSC involved in conyzasaponin biosynthesis.

SUBMITTER: Sun R 

PROVIDER: S-EPMC5623702 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature