Structural properties and immunomodulatory activity of an α-glucan purified from the fruiting body of Stropharia rugosoannulata

A novel polysaccharide PSRa-2 was purified from Stropharia rugosoannulata fruiting bodies using high pressure homogenization-assisted dual enzyme method, ion exchange, and gel chromatography. The PSRa-2 was characterized via FT-IR, HPAEC, SEM, Congo red test, SEC–MALLS-RI, methylation analysis, and NMR analysis. Structural characterization revealed that PSRa-2 was an α-glucan with a Mw 455.6 kDa. The backbone of PSRa-2 was composed of →4)-α- d -Glc p -(1→ and →3)-α- d -Glc p -(1→ and branches of α- d -Glc p -(1→ at position O-6 of →4,6)-α- d -Glc p -(1→. PSRa-2 induced splenocyte proliferation and protected splenocytes against 5-Fu-induced immunosuppression by restoring the proliferation and secretion of cytokines (TNF-α and IL-2) secretion levels. Thus, PSRa-2 exhibits obviously immunomodulatory activity and represents a potential natural immunomodulator. Graphical Abstract