The arabinogalactan-proteins from pressed juice of Echinacea purpurea belong to the hybrid class of hydroxyproline-rich glycoproteins.

Pressed juices from Echinacea purpurea are used as non-specific immunostimulants, and arabinogalactan-proteins (AGPs) are part of the active principle. An AGP fraction was isolated from pressed juice of E. purpurea by precipitation with ss-glucosyl Yariv reagent, followed by gel-permeation chromatography. Polyclonal antibodies directed against the carbohydrate moiety of this AGP fraction showed a preferential specificity for E. purpurea AGPs from pressed juice over those extracted from E. purpurea suspension culture and other plant species. Native AGPs purified from this AGP fraction by RP-HPLC were then deglycosylated for N-terminal protein sequencing resulting in the identification of three major polypeptides. They show characteristic motifs of classical AGPs but also some features of extensins, suggesting these may be "hybrid" hydroxyproline-rich glycoproteins (HRGPs).