Preparation and immunomodulating activities of a library of low-molecular-weight α-glucans

YCP, an α-d-glucan with molecular weight of 2.4 × 103 kDa, was isolated from the mycelium of marine fungus Phoma herbarum YS4108. It interacted with TLR2 and TLR4 to induce B cells proliferation and activation. Here, a series of homogenous LMWYCPs (namely LMWYCP-1 to LMWYCP-6) were obtained by acid degradation. LMWYCP-3 and LMWYCP-4 were capable of inducing the proliferation of B cells dramatically. Further research involved TLR defunctionalization and competitive binding assay demonstrated that the immunomodulating activities of LMWYCP-4 was TLR4-dependent but TLR2-independent, while that mediated by LMWYCP-3 was neither TLR2- nor TLR4-dependent. Together with the structural information that LMWYCPs shared the similar structure features with YCP, we deduced that LMWYCP-4 may be the functional unit of YCP responsible for YCP/TLR4 interaction. This is the first time that the probable functional unit of glucan with the structure of α-d-(1–4)-linked residues in main chain and α-d-(1–6)-linked residues in branches is reported.