Prediction of C-glycosylated apigenin (vitexin) biosynthesis in Ficus deltoidea based on plant proteins identified by LC-MS/MS

Abstract

Background: Plant secondary metabolites act as defence molecules to protect plants from biotic and abiotic stresses. In particular, C-glycosylated flavonoids are more stable and reactive than their O-glycosylated counterparts. Therefore, vitexin (apigenin 8-C glucoside) present in Ficus deltoidea is well-known for its antioxidant, anti-inflammatory, and antidiabetic properties. Methods: Phenol based extraction was used to extract proteins (0.05% yield) with less plant pigments. This can be seen from clear protein bands in gel electrophoresis. In-gel trypsin digestion was subsequently carried out and analysed for the presence of peptides by LC-MS/MS. Results: Thirteen intact proteins are identified on a 12% polyacrylamide gel. The mass spectra matching was found to have 229 proteins, and 11.4% of these were involved in secondary metabolism. Proteins closely related to vitexin biosynthesis are listed and their functions are explained mechanistically. Vitexin synthesis is predicted to involve plant polyketide chalcone synthase, isomerization by chalcone isomerase, oxidation by cytochrome P450 to convert flavanone to flavone, and transfer of sugar moiety by C-glycosyltransferase, followed by dehydration to produce flavone-8-C-glucosides. Conclusions: Phenol based extraction, followed by gel electrophoresis and LC-MS/MS could identify proteome explaining vitexin biosynthesis in F. deltoidea. Many transferases including β-1,3-galactosyltransferase 2 and glycosyl hydrolase family 10 protein were detected in this study. This explains the importance of transferase family proteins in Cglycosylated apigenin biosynthesis in medicinal plant.