Polysaccharides from lichen Xanthoria parietina: 1,4/1,6-α-d-glucans and a highly branched galactomannan with macrophage stimulating activity via Dectin-2 activation
2019
Rashid, Zalilawati Mat | Mormann, Michael | Steckhan, Katja | Peters, Alena | Esch, Stefan | Hensel, Andreas
Hot-water soluble polysaccharides H-1-3 and H-2-1 were isolated from the thalli of the lichen Xanthoria parietina (L.) Th. Fr. and purified by ion exchange and gel permeation chromatography. Structure elucidation was mainly based on 2D-NMR and nano-ESI-Q-TOF MS/MS experiments.H-1-3 (13.7 kDa) was shown to be linear α-glucan with α-d-Glcp-(1 → [→[4)-α-d-Glcp-(1]2 → [6)-α-d-Glcp-(1]3 → 4)]n core backbone. The (1,4)- and (1,6)-α-d-Glcp linkages were in a 2:3 M ratio.H-2-1 (525 kDa) was characterized as a complex branched β-galacto-α-mannan with →[6)-α-d-Manp-(1 → [2,6)-α-d-Manp-(1]2 → [2)-α-d-Manp-(1]2→]n core units and main side chains of (1,3)-β-d-Galf linked at O-6 to →2)-α-d-Manp-(1→, together with minor terminal units of 1,4/1,6-α-D -Glcp units attached to the core chain at O-6 position and α-L-Rhap linked to Galf side chain at O-2 position (Manp: Galf: Glcp: Rhap linkage ratio = 9:3:2:1).H-2-1 exerted strong immunoactivity in vitro and activated murine RAW macrophages 264.7 towards significantly increased phagocytosis, TNF-α and IL-1β secretion. These effects are due to an interaction of the galactomannan with the transmembrane pattern-recognition protein Dectin-2 of the macrophages.
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