MALDI Imaging Assisted Discovery of a Di-O-glycosyltransferase from Platycodon grandiflorum Root

A matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) assisted genome mining strategy was developed for the discovery of glycosyltransferase (GT) from the root of Platycodon grandiflorum. A di-O-glycosyltransferase PgGT1 was discovered and characterized that is capable of catalyzing platycoside E (PE) synthesis through the attachment of two beta-1,6-linked glucosyl residues sequentially to the glucosyl residue at the C3 position of platycodin D (PD). Although UDP-glucose is the preferred sugar donor for PgGT1, it could also utilize UDP-xylose and UDP-N-acetylglucosamine as weak donors. Residues S273, E274, and H350 played important roles in stabilizing the glucose donor and positioning the glucose in the optimal orientation for the glycosylation reaction. This study clarified two key steps involved in the biosynthetic pathway of PE and could greatly contribute to improving its industrial biotransformation.

Automated summary

A matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) assisted genome mining strategy was applied to discover a glycosyltransferase (GT) named PgGT1 from the root of Platycodon grandiflorum. PgGT1 was found to catalyze the synthesis of platycoside E (PE) by sequentially attaching two beta-1,6-linked glucosyl residues to the glucosyl residue at the C3 position of platycodin D (PD). The study also revealed the crucial roles of residues S273, E274, and H350 in stabilizing the sugar donor and positioning the glucose for optimal glycosylation. These findings provide insights into the biosynthetic pathway of PE and have potential implications in industrial biotransformation.