Mining and characterization of a novel cytochrome P450 MaCYP71BG22 involved in the C4-stereoselective hydroxylation of 1-deoxynojirimycin biosynthesis in mulberry leaves
1-Deoxynojirimycin (DNJ), a primary active component in mulberry leaves, has garnered significant attention due to its unique structure and notable pharmacological properties. Our previous investigations have elucidated the biosynthetic pathways of DNJ from lysine to 2-methylpiperidine. However, the hydroxylation process and its underlying mechanisms remain elusive. In this study, five CYP450s hydroxylase genes significantly correlated ( P < 0.05) with DNJ content in mulberry leaves at various time were screened through transcriptome profile. MaCYP71BG22 was first cloned and functionally characterized. This gene was shown to specifically catalyze the stereoselective hydroxylation of ( R )-2-methylpiperidine at the C4-position to produce (2 R , 4 R )-2-methylpiperidin-4-ol. In hairy roots of mulberry, overexpression of MaCYP71BG22 increased DNJ accumulation, while virus-induced gene silencing (VIGS) decreased its production. Furthermore, structural-function analysis pinpointed a critical residue, G460, in MaCYP71BG22, mutation of this residue to G460E enhanced the enzyme's catalytic efficiency. This study represents the first report of a CYP450 hydroxylase involved in the biosynthesis of piperidine alkaloids in mulberry leaves, and demonstrates that MaCYP71BG22 selectively catalyzes the C4-stereoselective hydroxylation of ( R )-2-methylpiperidine in DNJ biosynthesis. These findings further elucidate the DNJ biosynthetic pathway and provide new insights into the stereo- and regio-selective hydroxylation abilities of CYP450s hydroxylase in DNJ biosynthesis.
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