Glycosylation reduces the glycan-independent immunomodulatory effect of recombinant Orysata lectin in Drosophila S2 cells

Several plant lectins, or carbohydrate-binding proteins, interact with glycan moieties on the surface of immune cells, thereby influencing the immune response of these cells. Orysata, a mannose-binding lectin from rice, has been reported to exert immunomodulatory activities on insect cells. While the natural lectin is non-glycosylated, recombinant Orysata produced in the yeast Pichia pastoris (YOry) is modified with a hyper-mannosylated N-glycan. Since it is unclear whether this glycosylation can affect the YOry activity, non-glycosylated rOrysata was produced in Escherichia coli (BOry). In a comparative analysis, both recombinant Orysata proteins were tested for their carbohydrate specificity on a glycan array, followed by the investigation of the carbohydrate-dependent agglutination of red blood cells (RBCs) and the carbohydrate-independent immune responses in Drosophila melanogaster S2 cells. Although YOry and BOry showed a similar carbohydrate-binding profiles, lower concentration of BOry were sufficient for the agglutination of RBCs and BOry induced stronger immune responses in S2 cells. The data are discussed in relation to different hypotheses explaining the weaker responses of glycosylated YOry. In conclusion, these observations contribute to the understanding how post-translational modification can affect protein function, and provide guidance in the selection of the proper expression system for the recombinant production of lectins.