Glycosylation of Ganoderic Acid G by Bacillus Glycosyltransferases

Abstract

Ganoderma lucidum is a medicinal fungus abundant in triterpenoids, its primary bioactive components. Although numerous Ganoderma triterpenoids have already been identified, rare Ganoderma triterpenoid saponins were recently discovered. To create novel Ganoderma saponins, ganoderic acid G (GAG) was selected for biotransformation using four Bacillus glycosyltransferases (GTs) including BtGT_16345 from the Bacillus thuringiensis GA A07 strain and three GTs (BsGT110, BsUGT398, and BsUGT489) from the Bacillus subtilis ATCC 6633 strain. The results showed that BsUGT489 catalyzed the glycosylation of GAG to GAG-3-o-β-glucoside, while BsGT110 catalyzed the glycosylation of GAG to GAG-26-o-β-glucoside, which showed 54-fold and 97-fold greater aqueous solubility than that of GAG, respectively. To our knowledge, these two GAG saponins are new compounds. The glycosylation specificity of the four Bacillus GTs highlights the possibility of novel Ganoderma triterpenoid saponin production in the future.

Keywords: Bacillus; Ganoderma lucidum; glycosyltransferase; saponin; triterpenoid.

Figure 1

Seven known bacterial glycosyltransferases (GTs) from previous studies. The phylogenetic tree was adopted from Figure 1 in the study by Chang et al. [14].

Figure 2

The chemical structure of ganoderic acid G (GAG).

Figure 3

High-performance liquid chromatography (HPLC) results of the biotransformation products of GAG using the four Bacillus GT enzymes. The biotransformation and HPLC conditions are described in the Materials and Methods section.

Figure 4

The biotransformation process of GAG to GAG saponins by the Bacillus GTs.

Figure 5

The glycosylation of GAA and GAG by the four Bacillus GTs.