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In Vitro Characterization of the Aromatic SAM-Dependent C-Methyltransferase NapB5
Juliane Breiltgens1, Alexandra Paul1, Ziruo Zou1
1Institute of Pharmaceutical Sciences, University of Freiburg, Albertstr. 25, 79104 Freiburg, Germany.
Journal of Natural Products
|October 30, 2025
Summary
This study characterizes NapB5, an S-Adenosyl-l-methionine (SAM)-dependent C-methyltransferase involved in napyradiomycin biosynthesis. NapB5 demonstrates selective C-methylation of natural product building blocks, revealing insights into enzyme selectivity mechanisms.
Area of Science:
- Natural Product Biosynthesis
- Enzymology
- Structural Biology
Background:
- Aromatic polyketide synthases (PKS) produce diverse natural products.
- S-Adenosyl-l-methionine (SAM)-dependent C-methyltransferases (C-MTs) are key enzymes in natural product diversification.
- Napyradiomycins are a class of meroterpenoid natural products with complex structures.
Purpose of the Study:
- To characterize the C-methyltransferase NapB5 from Streptomyces aculeolatus.
- To elucidate the mechanism of substrate selectivity in NapB5.
- To identify homologous C-MTs in other actinomycetes for understanding natural product diversity.
Main Methods:
- Biochemical characterization of NapB5 enzyme activity.
- Structure-guided mutagenesis and protein-ligand docking studies.
- Comparative analysis of gene clusters in actinomycetes.
Main Results:
- NapB5 catalyzes C2 monomethylation of 1,3,6,8-tetrahydroxynaphthalene (T4HN).
- NapB5 exhibits chemoselective C-dimethylation of both T4HN and flaviolin in vitro.
- Enzyme structure and substrate positioning are critical for regio- and chemoselectivity.
Conclusions:
- NapB5's selectivity is governed by precise substrate positioning relative to the SAM methyl donor.
- Homologous C-MTs in other actinomycetes likely contribute to naphthoquinone-based meroterpenoid diversity.
- Understanding these enzymes provides insights into generating novel natural product analogs.
