Improvement of cannabidiolic acid synthetase activity through molecular docking and site-directed mutagenesis

Abstract

Cannabidiol (CBD), a nonhallucinogenic but therapeutic compound, is widely used in fields such as medicine, food, health products, and cosmetics. Cannabidiolic acid synthase (CBDAS) can exclusively catalyze the conversion of cannabigerolic acid (CBGA), which is the common precursor of cannabinoids, to CBDA, which is then decarboxylated to form CBD. In order to determine which amino acids in the CBDAS protein undergo mutations that can significantly enhance the catalytic activity of the enzyme, molecular docking and experimental validation were performed in this study. The CBDAS gene was cloned from a high-CBD-content hemp germplasm; this 1635 base pair gene encodes 544 amino acids. Saturation and alanine scanning mutagenesis and combinatorial mutation analysis showed that a single amino acid mutation (C176W) and three dual mutations (H69G+H114L, H114L+C176W and G183V+N482W) in CBDAS reduced the binding energy of the mutant for the substrate CBGA. The molecular docking results indicated that for the mutants CBDASH114L+C176W and CBDASG183V+N482W, the interaction force with CBGA was increased, the bond distance was shortened, and some amino acids that interacted with the substrate were also altered compared with the WT. For the mutants CBDASC176W and CBDASH69G+H114L, compared with the WT, the interaction force with CBGA was decreased, or the interaction was eliminated. The results of enzyme catalytic activity measurement showed that compared with the WT, the catalytic activities of CBDASG183V+N482W and CBDASH114L+C176W were significantly increased, and that of CBDASH69G+H114L was significantly decreased (P < 0.05), which was generally consistent with the expected results from molecular docking. The crude leaf extract, when used as the substrate, produced more CBDA and CBD than an equal concentration of the CBGA standard. Obviously, it is possible that the recombinant CBDAS produced with yeast mutants can be used for secondary production of CBD in the process of cannabinoid extraction with the remaining CBGA in the leaves as the substrate. The research results provide a theoretical basis for the molecular modification of other cannabinoid synthetases.