Structural analysis of arabinogalactan-proteins from suspension cultures of Pelargonium sidoides DC.

Pelargonium sidoides DC. is a traditional medicinal plant from South Africa. An aqueous-ethanolic formulation of the roots is approved for the treatment of acute bronchitis. The main effects could be related to antibacterial activities and the stimulation of the non-specific immune system by the main components of Pelargonium sidoides: coumarins, phenols and tannins [1].

Due to wild harvesting, Pelargonium sidoides is an endangered species. Therefore the propagation of the plant material by cell cultures and the extraction of ingredients are interesting tasks.

From suspension cultures of Pelargonium sidoides high amounts of pure Arabinogalactan-proteins (AGPs) could be isolated by precipitation with β-glucosyl Yariv reagent. These AGPs have been investigated with regard to their structure.

Quantification of neutral sugars by acetylation pointed out arabinose (Ara) and galactose (Gal) as dominating monosaccharide residues in a ratio of 1:2. Colourimetric determination of uronic acids revealed an amount of 6–8%. Linkage type analysis in combination with the reduction of the uronic acids showed that the main components are 1,3,6-Gal(p), 1,3-Gal(p) and 1-Ara(f) as well as minor amounts of 1,6-Gal(p), 1-GlcA(p), 1,4-Gal(p), 1-Gal(p), 1,5-Ara(f) and 1,2-Ara(f). Molecular weight of AGPs has been determined by size exclusion chromatography with laser light scattering detection and found to range between 80 and 85 kDa. The characterisation of the AGP-protein moiety pointed out an untypical low protein content for AGPs with 1%. According to the amino acid analysis the protein moiety consists of high amounts of Hyp (42.8–51.1%) as well as Pro, Gly, Glx, Asx, Ser, Ala, Leu and Thr.

References: 1. Kolodziej H (2008) Planta Med 74: 661–666