The structural characterization of a polysaccharide exhibiting antitumor effect from Pholiota adiposa mycelia

PAP80-2a, purified from Pholiota adiposa mycelia, is a polysaccharide exhibiting prominent antitumor effects. However, the yield of PAP80-2a was low and its structure has not been characterized, impeding the exploration of its structure-function relationship, thus influencing the development of oral drugs for antitumor therapy and immunomodulation. In order to improve the yield of PAP80-2a, response surface methodology along with Box-Behnken design was applied to optimize the ultrasonic-assisted extraction conditions for polysaccharides. Then, the structure of PAP80-2a exhibiting antitumor activity was determined from different angles. The results showed that the extraction yield of P. adiposa polysaccharides increased by 11.5% under optimized ultrasonic extraction conditions. Structural analysis showed that PAP80-2a was mainly composed of glucose, rhamnose, xylose, and galactose in a ratio of 10.00: 2.09: 4.09: 1.13. The total amino acid content in the sugar chain was 69.92 μg/mL. The sugar chain structure was [α-Rha (1 → 3)-]n, and rhamnose was located at the non-reducing end of the sugar chain, while glucose was located at the non-reducing end or in the sugar chain in 1,2,6- and 1,3,6-linked forms. Our study clearly illuminates the primary structure of PAP80-2a, but 3D structure of PAP80-2a and its structure–function relationship is a future challenge.