Multiple NADPH-cytochrome P450 reductases from Lycoris radiata involved in Amaryllidaceae alkaloids biosynthesis

Amaryllidaceae alkaloids (AAs), such as galanthamine and lycorine, are natural products of Lycoris radiata possessing various pharmacological activities including anti-acetylcholinesterase, anti-inflammatory, and antitumour activities. Elucidating the biosynthesis of these special AAs is crucial for understanding their production and potential modification for improved clinical application, of which cytochrome P450 enzymes catalyse the formation of key alkaloid skeletons and subsequent modification processes, with the NAPDH cytochrome P450 reductases (CPRs) serving as essential redox partners. This study identified three CPRs, LrCPR1, LrCPR2, and LrCPR3, encoding 700, 697 and 695 amino acids, respectively, which belong to Class II CPRs. The LrCPRs reduced cytochrome c and ferricyanide in an NADPH-dependent manner, and their activities all followed the typical Michaelis-Menten curve. In yeast, the co-expression of LrCPRs and CYP96T6 produced the galantamine-like alkaloid namely N-demethylnarwedine, suggesting that they support the catalytic activity of CYP96T6. Quantitative analysis of the transcriptional expression profiles showed that LrCPRs were expressed in all the examined tissues of L. radiata, and their gene expression patterns are consistent with other genes that may be involved in the biosynthetic pathway of AAs, including cinnamate 4-hydroxylase and phenylalanine ammonia-lyase. Our study firstly provides the functional characterization of LrCPRs in L. radiata, which will contribute to the discovery of biosynthetic pathways and heterologous production of AAs.