Structural Characterization and Immunomodulatory Activity of Two Homogalacturonan-Type Pectic Polysaccharides from Fruits of (Turcz.) Baill.

Two homogalacturonan (HG)-type pectic polysaccharides, (, 5.37 × 10 g/mol) and (, 6.10 × 10 g/mol), were isolated from fruits. Their structures were determined to consist of repeating units of →1)-αd-GalA-(4→, exhibiting varying degrees of esterification based on multiple chromatographic analysis techniques. The possible distribution of methyl esters in the HG region of and was elucidated using endopolygalacturonase (endo-PG) hydrolysis combined with HILIC-ESI-QTOF-MS/MS and UPSEC-ESI-MS. Surface plasmon resonance analysis revealed that both ( = 1.12 × 10 and 2.27 × 10 M for TLR2/4) and ( = 4.80 × 10 and 6.68 × 10 M for TLR2/4) exhibited strong binding affinities to TLR2/4. However, showed approximately twice the affinity for TLR2/4 than . The in vitro assessment of immunomodulatory activity further confirmed that significantly promoted the secretion of NO and upregulated the levels of TNF-α and IL-6 more effectively than . These results indicate that may display a more significant immune activation capability due to its higher affinity for TLR2/4.