Beyond the cyclopropyl ring formation: fungal Aj_EasH catalyzes asymmetric hydroxylation of ergot alkaloids

Ergot alkaloids (EAs) are among the most important bioactive natural products. Fe-II/alpha-ketoglutarate-dependent dioxygenase Aj_EasH from Aspergillus japonicus is responsible for the formation of the cyclopropyl ring of the ergot alkaloid (EA) cycloclavine (4). Herein we reconstituted the biosynthesis of 4 in vitro from prechanoclavine (1) for the first time. Additionally, an unexpected activity of asymmetric hydroxylation at the C-4 position of EA compound festuclavine (5) for Aj_EasH was revealed. Furthermore, Aj_EasH also catalyzes the hydroxylation of two more EAs 9,10-dihydrolysergol (6) and elymoclavine (7). Thus, our results proved that Aj_EasH is a promiscuous and bimodal dioxygenase that catalyzes both the formation of cyclopropyl ring in 4 and the asymmetric hydroxylation of EAs. Molecular docking (MD) revealed the substrate-binding mode as well as the catalytic mechanism of asymmetric hydroxylation, suggesting more EAs could potentially be recognized and hydroxylated by Aj_EasH. Overall, the newly discovered activity empowered Aj_EasH with great potential for producing more diverse and bioactive EA derivatives.

Automated summary

Ergot alkaloids are important bioactive natural products. The dioxygenase Aj_EasH from Aspergillus japonicus has been found to catalyze both the formation of the cyclopropyl ring in cycloclavine and the asymmetric hydroxylation of other ergot alkaloids. Molecular docking studies revealed the substrate binding and catalytic mechanism, suggesting the potential of Aj_EasH for producing diverse and bioactive ergot alkaloid derivatives.