Structural characteristics of Saccharomyces cerevisiae mannoprotein and its immunomodulatory activities on RAW264.7 cells

An enzyme-extracted mannoprotein (SC-MP) from the cell wall of Saccharomyces cerevisiae was investigated for structural characteristics and immunomodulatory effects on RAW264.7. The SC-MP was purified using the diethylaminoethyl (DEAE) cellulose column and gel column to isolate 2 fractions (MP-1 and MP-2), with MP-1 as the dominant fraction (yield, 87.4 %). The results of composition analyses showed that MP-1, which comprises 88.13 % (w/w) sugar and 6.93 % (w/w) protein, had lower protein content than SC-MP (20.89 %, w/w). Monosaccharide analysis showed MP-1 comprises mannose, glucose, and glucosamine in a molar ratio of 97.64:1.46:0.38. The molecule weight of MP-1 was 141 kDa. The MP-1 was further analyzed using GC-MS, NMR to elucidate its structural characteristics, the results showed that the main sugar residue types of MP-1 included T-D-Manp (45.41 mol%), 1,2,6-D-Manp (21.58 mol%), 1,2-D-Manp (19.45 mol%), and 1,6-D-Manp (6.06 mol%), 1,3-D-Manp (3.91 mol%), and a little amount of 1,6-D-Glcp (3.59 mol%). The mannoses polymerized to form mannan and mano-oligosaccharide. Mannan, which has α-1,6-mannan backbone branched with α-1,2-mannan and α-1,3-mannan, connected to protein by N-glycosylation (via asparagine), and mano-oligosaccharide connected to protein by O-glycosylation (via serine or threonine). At 150 μg/mL concentrations, SC-MP and MP-1, which were different in purity, significantly stimulated the secretion of TNF-α and inhibited the secretion of IL-10 of RAW 264.7 cells, and MP-1 showed stronger effects. This study provided a scientific basis for further exploring the applications of yeast mannoprotein.