Effect of purification of galactooligosaccharides derived from lactulose with Saccharomyces cerevisiae on their capacity to bind immune cell receptor Dectin-2

Lactulose-derived oligosaccharides (OsLu) are prebiotic galactooligosaccharides (GOS) known to be beneficial for human health. Many of these carbohydrates are reported to have immunomodulatory properties; however the molecular mechanism is unclear. OsLu produced by enzymatic synthesis can be purified with Saccharomyces cerevisiae (OsLu-Sc). We show that this purification method introduces yeast-derived proteins reactive to Dectin-2, an innate immune receptor for fungal polysaccharides. Using a cell-based bioassay, we tested the binding of OsLu and GOS samples to Dectin-2. While OsLu purified with active charcoal and commercial GOS failed to bind to Dectin-2, we found OsLu-Sc bound to this receptor. The carbohydrate-binding incompetent mutant of Dectin-2 failed to bind to OsLu-Sc. These data suggest that OsLu-Sc introduced carbohydrate ligands for Dectin-2. In accordance with this, proteomic analysis revealed OsLu-Sc contained S. cerevisiae-derived mannoproteins. Therefore, our data highlights the importance of the purification method for OsLu, which may positively affect the bioactivity of OsLu.