Characterization of a new microbial Pictet-Spenglerase NscbB affording the β-carboline skeletons from Nocardiopsis synnemataformans DSM 44143

The enzymatic Pictet-Spengler (PS) reaction, catalyzed by Pictet-Spenglerase (PSase), is the feature of β-carboline (βC) alkaloid biosynthesis. NscbB is a rare microbial PSase discovered from a cryptic β-carboline alkaloid biosynthetic gene cluster (BGC) in the Nocardiopsis synnemataformans DSM 44143 (kidney transplant patient derived) by homologous alignment with its well-characterized counterpart McbB. The biochemical analysis showed that NscbB could catalyze l-tryptophan (KM = 89.64 ± 8.69 μM) and methylglyoxal (KM = 147.70 ± 16.38 μM), without cofactors, to form the two βC skeletons 1-acetyl-3-carboxy-β-carboline and 1-acetyl-β-carboline in vitro. Additionally, the heterologous expression of nscbB in E. coli BL21 (DE3) revealed the efficient bioproductivity of NscbB to bioproduce two βC skeletons, 1-acetyl-3-carboxy-β-carboline (5.5 mg/L) and 1-acetyl-β-carboline (3.1 mg/L), within 16 h fermentation. These results demonstrate NscbB is a novel and practical microbial PSase, which is useful for future bioactive βC alkaloid exploitation and development.