The C-glycosidic bond that connects the sugar moiety with aglycone is difficult to be broken or made due to its inert nature. The knowledge of C-glycoside breakdown and synthesis is very limited. Recently, the enzyme DgpA/B/C cascade from a human intestinal bacterium PUE was identified to specifically cleave the C-glycosidic bond of puerarin (daidzein-8-C-glucoside). Here we investigated how puerarin is recognized and oxidized by DgpA based on crystal structures of DgpA with or without substrate and biochemical characterization. More strikingly, we found that apart from being a C-glycoside cleaving enzyme, DgpA/B/C is capable of efficiently converting O- to C-glycoside showing the activity as a structure isomerase. A possible mechanistic model was proposed dependently of the simulated complex structure of DgpB/C with 3″-oxo-daidzin and structure-based mutagenesis. Our findings not only shed light on understanding the enzyme-mediated C-glycosidic bond breakage and formation, but also may help to facilitate stereospecific C-glycoside synthesis in pharmaceutical industry.

Gymnosperms represent an ancient lineage with diverse chemical profiles. Their terpenoids constitute a major class notable for substantial structural diversity. Terpene synthases (TPSs) are the driving force of terpene diversity. TPS-d is a gymnosperm-specific TPS subfamily, yet the evolution and functional diversity of TPS-d are still understudied. In this review, we analyze 134 functionally characterized gymnosperm TPSs to elucidate the evolutionary history and functional diversity of the predominant TPS-d subfamily. Phylogenetic analysis revealed substantial lineage-specific expansion and divergence within the TPS-d subfamily post-speciation. Crucially, we highlight the shifts in domain architecture during TPS-d evolution, providing structural evidence for the progressive attrition and eventual loss of the ancestral γ domain in TPS-d2 and TPS-d1 clades. Furthermore, we summarize the functional diversity of TPS-d enzymes in specialized metabolites, emphasizing their ecological roles in plant defense. Overall, this review provides a comprehensive overview of the evolutionary and functional landscape of the gymnosperm-specific TPS-d subfamily, serving as a valuable reference for future studies on TPSs in gymnosperms.