Elucidation and biological activities of a new polysaccharide from cultured Cordyceps militaris

•A novel low-molecular-weight polysaccharide was isolated from Cordyceps militaris.•The preliminary structural characterization of CMP-1 was conducted.•The ultrastructure of CMP-1 was investigated by scanning electron microscope (SEM).•The antioxidant, immunostimulatory and antitumor activities of CMP-1 were evaluated.•CMP-1 may be considered as a potential candidate for antitumor agent. A novel low-molecular-weight polysaccharide (CMP-1) with antioxidant, immunostimulatory and antitumor activities was isolated from the cultured Cordyceps militaris. The structure of CMP-1 was elucidated by a combination of physicochemical and instrumental analyses, and its average molecular weight was 4.3kDa. The backbone of CMP-1 was composed of (1→4)-linked α-d-glucopyranosyl, (1→6)-linked β-d-glucopyranosyl and (1→4)-linked β-d-glucopyranosyl residues which branched at O-6. The branches consisted of (1→3)-linked α-l-rhamnopyranosyl terminated with (1→)-linked α-d-glucopyranosyl residues. The ultrastructure of CMP-1 was further investigated by scanning electron microscope (SEM). The antioxidant assays showed that CMP-1 exhibited free radical-scavenging effects, ferrous ions-chelating ability and reducing power. In vitro test revealed that CMP-1 could significantly stimulate the mouse splenocyte proliferation. The cytotoxicity assay showed that CMP-1 inhibited the proliferation of HT-29, HeLa, HepG2 and K562 cells, with the IC50 values of 137.66, 162.59, 176.29 and 364.01μg/mL, respectively.