Characterization of a polysaccharide from Rhodobryum giganteum and its activation effects on TLR4/PI3K-Akt/IκBα pathway

The medicinal moss Rhodobryum giganteum is rich in polysaccharides, whose structural and biofunctional properties remain largely unexplored. In this study, a novel glucose-rich polysaccharide fraction (named RGP, 29.8 kDa) was isolated and characterized from R. giganteum . Structural analysis revealed a unique α -1,6-linked glucan backbone with C-2 acetylation, along with side chains composed of →4)- α - d -glucopyranosyl-(1 → and terminal α - d -glucopyranose units. RGP significantly promoted proliferation, phagocytosis, and cytokine (TNF- α , IL-6) secretion via the TLR4/PI3K-Akt/IκB α pathway in RAW264.7 cells. In immunosuppressed mice, RGP restored immune function, as shown by improved organ indices, elevated serum immunoglobulins (IgA, IgG, IgM), and alleviated splenic damage. Molecular docking revealed that RGP binds the hydrophobic pocket of the TLR4/PI3K-Akt/IκB α complex via its glucose chain, and dynamics simulations confirmed the stability of this interaction. These findings reveal the bioactivity of bryophyte polysaccharides and suggest RGP as a potential immunomodulatory agent.