Catalytic promiscuity of O-methyltransferases from Corydalis yanhusuo leading to the structural diversity of benzylisoquinoline alkaloids

Characterization of CYP82 genes involved in the biosynthesis of structurally diverse benzylisoquinoline alkaloids in Corydalis yanhusuo

Benzylisoquinoline alkaloids (BIAs) represent a significant class of secondary metabolites with crucial roles in plant physiology and substantial potential for clinical applications. CYP82 genes are involved in the formation and modification of various BIA skeletons, contributing to the structural diversity of compounds. In this study, Corydalis yanhusuo, a traditional Chinese medicine rich in BIAs, was investigated to identify the catalytic function of CYP82s during BIA formation. Specifically, 20 CyCYP82-encoding genes were cloned, and their functions were identified in vitro. Ten of these CyCYP82s were observed to catalyze hydroxylation, leading to the formation of protopine and benzophenanthridine scaffolds. Furthermore, the correlation between BIA accumulation and the expression of CyCYP82s in different tissues of C. yanhusuo was assessed their. The identification and characterization of CyCYP82s provide novel genetic elements that can advance the synthetic biology of BIA compounds such as protopine and benzophenanthridine, and offer insights into the biosynthesis of BIAs with diverse structures in C. yanhusuo.

O- and N-Methyltransferases in benzylisoquinoline alkaloid producing plants

BACKGROUND

Secondary metabolites such as benzylisoquinoline alkaloids (BIA) have attracted considerable attention because of their pharmacological properties and potential therapeutic applications. Methyltransferases (MTs) can add methyl groups to alkaloid molecules, altering their physicochemical properties and bioactivity, stability, solubility, and recognition by other cellular components. Five types of O-methyltransferases and two types of N-methyltransferases are involved in BIA biosynthesis.

OBJECTIVE

Since MTs may be the source for the discovery and development of novel biomedical, agricultural, and industrial compounds, we performed extensive molecular and phylogenetic analyses of O- and N-methyltransferases in BIA-producing plants.

METHODS

MTs involved in BIA biosynthesis were isolated from transcriptomes of Berberis koreana and Caulophyllum robustum. We also mined the methyltransferases of Coptis japonica, Papaver somniferum, and Nelumbo nucifera from the National Center for Biotechnology Information protein database. Then, we analyzed the functional motifs and phylogenetic analysis.

RESULT

We mined 42 O-methyltransferases and 8 N-methyltransferases from the five BIA-producing plants. Functional motifs for S-adenosyl-L-methionine-dependent methyltransferases were retained in most methyltransferases, except for the three O-methyltransferases from N. nucifera. Phylogenetic analysis revealed that the methyltransferases were grouped into four clades, I, II, III and IV. The clustering patterns in the phylogenetic analysis suggested a monophyletic origin of methyltransferases and gene duplication within species. The coexistence of different O-methyltransferases in the deep branch subclade might support some cases of substrate promiscuity.

CONCLUSIONS

Methyltransferases may be a source for the discovery and development of novel biomedical, agricultural, and industrial compounds. Our results contribute to further understanding of their structure and reaction mechanisms, which will require future functional studies.

Structure-function analysis of CYP719As involved in methylenedioxy bridge-formation in the biosynthesis of benzylisoquinoline alkaloids and its de novo production

Benzylisoquinoline alkaloids (BIAs) are a type of secondary metabolite with clinical application value. (S)-stylopine is a special BIA which contains methylenedioxy bridge structures. CYP719As could catalyze the methylenedioxy bridge-formation on the A or D rings of protoberberine alkaloids, while displaying significant substrate regiospecificity. To explore the substrate preference of CYP719As, we cloned and identified five CyCYP719A candidates from Corydalis yanhusuo. Two CyCYP719As (CyCYP719A39 and CyCYP719A42) with high catalytic efficiency for the methylenedioxy bridge-formation on the D or A rings were characterized, respectively. The residues (Leu 294 for CyCYP719A42 and Asp 289 for CyCYP719A39) were identified as the key to controlling the regioselectivity of CYP719As affecting the methylenedioxy bridge-formation on the A or D rings by homology modeling and mutation analysis. Furthermore, for de novo production of BIAs, CyCYP719A39, CyCYP719A42, and their mutants were introduced into the (S)-scoulerine-producing yeast to produce 32 mg/L (S)-stylopine. These results lay a foundation for understanding the structure-function relationship of CYP719A-mediated methylenedioxy bridge-formation and provide yeast strains for the BIAs production by synthetic biology.

Functional characterization and key residues engineering of a regiopromiscuity O-methyltransferase involved in benzylisoquinoline alkaloid biosynthesis in Nelumbo nucifera

Lotus (Nelumbo nucifera), an ancient aquatic plant, possesses a unique pharmacological activity that is primarily contributed by benzylisoquinoline alkaloids (BIAs). However, only few genes and enzymes involved in BIA biosynthesis in N. nucifera have been isolated and characterized. In the present study we identified the regiopromiscuity of an O-methyltransferase, designated NnOMT6, isolated from N. nucifera; NnOMT6 was found to catalyze the methylation of monobenzylisoquinoline 6-O/7-O, aporphine skeleton 6-O, phenylpropanoid 3-O, and protoberberine 2-O. We further probed the key residues affecting NnOMT6 activity via molecular docking and molecular dynamics simulation. Verification using site-directed mutagenesis revealed that residues D316, N130, L135, N176A, D269, and E328 were critical for BIA O-methyltransferase activities; furthermore, N323A, a mutant of NnOMT6, demonstrated a substantial increase in catalytic efficiency for BIAs and a broader acceptor scope compared with wild-type NnOMT6. To the best of our knowledge, this is the first study to report the O-methyltransferase activity of an aporphine skeleton without benzyl moiety substitutions in N. nucifera. The study findings provide biocatalysts for the semisynthesis of related medical compounds and give insights into protein engineering to strengthen O-methyltransferase activity in plants.