Structural characterization and immune-enhancing activity of a novel acid proteoglycan from Black soybean

Black soybean (Glycine max (L.) merr), as an edible seed of the leguminous plant, possesses a high amount of proteins and carbohydrates. However, few studies have been conducted on the protein-polysaccharide polymer (proteoglycan) in Black soybean. Here, we aim to characterize the proteoglycan in Black soybean. Firstly, a crude extract from Black soybean was obtained by water extraction and alcohol precipitation. Then, DEAE-52 cellulose and Sephadex G-100 column chromatography were used to isolate proteoglycans in the crude extract, and a novel proteoglycan named BBWPS2 was obtained. Moreover, the chemical analysis showed that BBWPS2 was a proteoglycan of 2.02 × 105 Da, and composed of 7 kinds of monosaccharides and 16 kinds of amino acids. β-elimination reaction identified the carbohydrate chain was connected to peptide chain with O-glycosidic bonds. Finally, the immunomodulatory tests indicated that BBWPS2 can significantly promote the primary splenocyte proliferation and activate mouse peritoneal macrophages to produce TNF-α. Subsequent pathway studies revealed that BBWPS2 activated macrophages through the mannose receptor-mediated NF-κB/MAPK signaling pathway. Our work indicated that BBWPS2 from Black soybean could be explored as a promising natural immunopotentiator in food and pharmaceutical industries.