Specific Glycosylation System Enables the High-Level and
Sustainable
Production of Glycyrrhetinic Acid 3‑O‑monoglucuronide
and Glycyrrhizin in Engineered Saccharomyces cerevisiae
posted on 2024-01-19, 09:29authored byBo Yang, Wentao Sun, Xinhe Liu, Ming-zhu Ding, Xudong Feng, Chun Li
Glycyrrhetinic acid 3-O-monoglucuronide
(GAMG)
and glycyrrhizin (GL) are typical pentacyclic triterpenoid saponins
present in licorice roots that exhibit important pharmacological properties.
GAMG and GL are sourced primarily from licorice, namely, “digging
roots and extracting acid”, which results in ecological imbalance
and environmental pollution. To overcome these issues, it is an eco-friendly
and sustainable alternative to de novo synthesize
GAMG and GL in Saccharomyces cerevisiae by coupling UDP-glucuronic acid and glycyrrhetinic acid (GA) under
the catalysis of glycosyltransferases. However, the reported productivity
is too low for industrial production. The primary limiting factors
include insufficient supply of precursors, poor activity, and low
specificity of the glycosyltransferases. In this study, we reconstructed
the GA-producing platform strain in which GA was mainly accumulated
intracellularly, making it suitable for subsequent glycosylation modifications.
Different glycosyltransferases were tested and selected in the platform
strain for achieving the efficient and specific synthesis of GAMG
and GL. Protein engineering of rate-limiting enzyme cUGT73P12 was
performed to further facilitate the conversion from GAMG to GL. The
glycosylation capacity of this system was assessed in vivo, uncovering that the insufficient supply of precursor GA limited
glycosylation modifications. Correspondingly, multiple metabolic engineering
strategies were applied to optimize the carbon flux distribution,
increasing the titers of GAMG and GL by 115.6 and 50.2%, respectively.
Finally, 552.9 mg/L GAMG and 476.6 mg/L GL were produced in the 5
L fed-batch fermentation, which were 238- and 79-fold higher than
previously reported values, respectively. The strategy described herein
can serve as a reference for the glycosylation of triterpenoids in
a cost-effective manner.