Two pectic polysaccharides from Stemona tuberosa Lour. roots with detailed structural features display potent immunoenhancing activity via TLR signaling pathway

Stemona tuberosa Lour., a noted traditional Chinese medicine, exerts potent pharmacological effects, yet its key pectic polysaccharides, especially their chemical structures, remain poorly understood, impeding further investigation and development. In this study, two pectin polysaccharides (STP-3-1 and STP-3-2) were isolated from the roots for the first time. Using HPLC, methylation-GC–MS, and 1D/2D NMR, their structures were elucidated. Both contain a rhamnogalacturonan I (RG-I) backbone with 1,5-α-arabinan and 1,4-β-galactan side chains; STP-3-1 is exclusively RG-I with higher galactose content, whereas STP-3-2 also harbors an α-1,4-homogalacturonan segment, α-L-Rha p -(1→, Δ4,5-α-D-Gal p A-(1 → residues, and methyl-esterified →4)-α-Gal p A-(1 → units. Immunological assays showed both polymers dose-dependently induced NO, TNF-α, and IL-6 production and their mRNA expression via the TLR pathway, with STP-3-2 displaying stronger activity, likely due to its lower molecular weight and higher homogalacturonan content. These findings reveal S. tuberosa polysaccharides as promising immunopotentiators. Their rigorously defined architectures offer exact molecular blueprints for mechanistic and pharmaceutical studies, while their exceptionally clear NMR spectra set a high-confidence reference for future pectic-polysaccharide research.