Endogenous calcium attenuates the immunomodulatory activity of a polysaccharide from Lycium barbarum L. leaves by altering the global molecular conformation

A heteropolysaccharide, LP5, was purified from Lycium barbarum L. leaves. It was identified as a calcium-rich polysaccharide (8.6 mg calcium/g) with a molecular weight of 2.50 × 105 Da. The polysaccharide was composed of six kinds of monosaccharides, of which mannose and xylose are the main components. And it contains 16.37% glucuronic acid. Studies on RAW264.7 cells demonstrated that this polysaccharide exhibited potent immunomodulatory activity, including an increase in phagocytic activity, as well as the release of both nitric oxide and cytokines. However, after the depletion of calcium, the polysaccharide exhibited greater immunomodulatory activity (p < 0.05). Further conformation analysis confirmed that the polysaccharide changed from a compact spherical conformation to a random coil structure in aqueous solution after the depletion of calcium, which resulted in increased immunomodulatory activity by LP5.