Construction of an artificial system for ambrein biosynthesis and investigation of some biological activities of ambrein

Metabolic engineering of Saccharomyces cerevisiae for high-level production of (+)-ambrein from glucose

(+)-Ambrein is the primary component of ambergris, a rare product found in sperm whales (Physeter microcephalus). Microbial production using sustainable resources is a promising way to replace animal extraction and chemical synthesis. We constructed an engineered yeast strain to produce (+)-ambrein de novo. Squalene is a substrate for the biosynthesis of (+)-ambrein. Firstly, strain LQ2, with a squalene yield of 384.4 mg/L was obtained by optimizing the mevalonate pathway. Then we engineered a method for the de novo production of (+)-ambrein using glucose as a carbon source by overexpressing codon-optimized tetraprenyl-β-curcumene cyclase (BmeTC) and its double mutant enzyme (BmeTCY167A/D373C), evaluating different promoters, knocking out GAL80, and fusing the protein with BmeTC and squalene synthase (AtSQS2). Nevertheless, the synthesis of (+)-ambrein is still limited, causing low catalytic activity in BmeTC. We carried out a protein surface amino acid modification of BmeTC. The dominant mutant BmeTCK6A/Q9E/N454A for the first step was obtained to improve its catalytic activity. The yield of (+)-ambrein increased from 35.2 to 59.0 mg/L in the shake flask and finally reached 457.4 mg/L in the 2 L fermenter, the highest titer currently available for yeast. Efficiently engineered strains and inexpensive fermentation conditions for the industrial production of (+)-ambrein. The metabolic engineering tools provide directions for optimizing the biosynthesis of other high-value triterpenes.

Analysis of vitamin D receptor binding affinities of enzymatically synthesized triterpenes including ambrein and unnatural onoceroids

Onoceroids are a rare family of triterpenes. One representative onoceroid is ambrein, which is the main component of ambergris used as a traditional medicine. We have previously identified the onoceroid synthase, BmeTC, in Bacillus megaterium and succeeded in creating ambrein synthase by introducing mutations into BmeTC. Owing to the structural similarity of ambrein to vitamin D, a molecule with diverse biological activities, we hypothesized that some of the activities of ambergris may be induced by the binding of ambrein to the vitamin D receptor (VDR). We demonstrated the VDR binding ability of ambrein. By comparing the structure-activity relationships of triterpenes with both the VDR affinity and osteoclastic differentiation-promoting activity, we observed that the activity of ambrein was not induced via the VDR. Therefore, some of the activities of ambergris, but not all, can be attributed to its VDR interaction. Additionally, six unnatural onoceroids were synthesized using the BmeTC reactions, and these compounds exhibited higher VDR affinity than that of ambrein. Enzymatic syntheses of onoceroid libraries will be valuable in creating a variety of bioactive compounds beyond ambergris.

From Ambergris to (-)-Ambrox: Chemistry Meets Biocatalysis for Sustainable (-)-Ambrox Production

(-)-Ambrox, the most prominent olfactive component of ambergris is one of the most widely used biodegradable fragrance ingredients. Traditionally it is produced from the diterpene sclareol, modified and cyclized into (-)-ambrox by classical chemistry steps. The availability of the new feedstock (E)-β-farnesene produced by fermentation opened new pathways to (E,E)-homofarnesol as a precursor to (-)-ambrox. Combining chemical transformation of (E)-β-farnesene to (E,E)-homofarnesol and its enzymatic cyclization at the industrial scale to (-)-ambrox with an engineered squalene hopene cyclase illustrates the potential of biotechnology for a more sustainable process, thus meeting the increasing consumers' demand for sustainably produced high quality perfumery and consumer goods. This review traces back to the origin of ambergris and the search for the source of its mysterious odor, leading to the discovery of (-)-ambrox as its main olfactive principle. It discusses the plethora of ways explored for its synthesis from diverse starting materials and presents the development of a process with significantly improved carbon efficiency for the industrial production of (-)-ambrox as 100% renewable Ambrofix.