An immunomodulating pectic polymer from Glinus oppositifolius

Tentative structure of the pectic polymer GOA1 isolated from Glinus oppositifolius (• = GalA, □ = Rha, ■ = T-Rha, ▴ = Gal involved in AG-II, ▪ = Gal involved in AG-I, ▵ = T-Gal, ♦ = Ara, ♢ = T-Ara, ∘ = 4- O-Me GlcA/GlcA) An immunomodulating pectic polymer, GOA1, obtained from the aerial parts of the Malian medicinal plant Glinus oppositifolius (L.) Aug. DC. (Aizoaceae) has previously been reported to consist of arabinogalactans type I and II, probably linked to a rhamnogalacturonan backbone. To further elucidate the structure of the polymer GOA1, enzymatic degradation studies and weak acid hydrolysis were performed. Five different glycosidases were used, endo-α- d-(1 → 4)-polygalacturonase, exo-α- l-arabinofuranosidase, endo-α- l-(1 → 5)-arabinanase, endo-β- d-(1 → 4)-galactanase and exo-β- d-galactosidase. It appears that GOA1 may contain a structural moiety consisting of a 1,3-linked galactopyranosyl (Gal p) main chain with 1,6-linked Gal p side chains attached to position 6 of the main chain. The 1,6-linked Gal p side chain may be branched in position 3 with arabinofuranosyl (Ara f) side chains. A 1,4-linked Gal p backbone which might carry side chains or glycosyl units attached to position 3 is also a structural element in the polymer. We further show that GOA1 induce proliferation of B cells and the secretion of IL-1β by macrophages, in addition to a marked increase of mRNA for IFN-γ in NK-cells. To elucidate structure–activity relations the native polymer and the digested fractions were tested for complement fixing activity and intestinal immune stimulating activity. The partial removal of Ara f residues after enzymatic degradations did not affect the bioactivities, while the acid hydrolysed fraction showed reduced complement fixing activity. A decrease in Ara f units, 1,3,6-linked Gal p units and a partial hydrolysed rhamnogalacturonan backbone, in addition to a reduction in molecular weight are factors that might have contributed to reduced bioactivity.