Identification and functional validation of key enzymes related to polysaccharide biosynthesis in Platycodon...

Platycodon grandiflorus (Jacq.) A. DC., a herbaceous plant belonging to the Campanulaceae family, is recognized for its substantial medicinal properties, attributed to its rich composition of bioactive compounds, including polysaccharides, saponins, and flavonoids. The polysaccharide components have been shown to exhibit significant anti-obesity effects. However, there is a notable lack of research on the biosynthesis of polysaccharides in P. grandiflorus. This study aimed to identify and functionally validate key enzymes involved in the polysaccharide biosynthetic pathway of P. grandiflorus. Based on transcriptomic data, the researchers identified four genes associated with the polysaccharide biosynthetic pathway in P. grandiflorus, specifically including one phosphomannose isomerase gene (PgPMI), one phosphoglucose isomerase gene (PgGPI1), and two phosphomannose mutase genes (PgPMM1 and PgPMM2). The enzymatic activity of genes was verified in Escherichia coli, demonstrating that the recombinant PgPMI protein catalyzes the interconversion of mannose-6-phosphate and fructose-6-phosphate. Additionally, the recombinant PgPMM1 and PgPMM2 proteins were shown to catalyze the interconversion of mannose-1-phosphate and mannose-6-phosphate, while the recombinant PgGPI1 protein is capable of catalyzing the conversion of glucose-6-phosphate to fructose-6-phosphate. This study enhances knowledge of the polysaccharide biosynthetic pathway and underpins subsequent molecular research on polysaccharide metabolism and related physiology.