Fine-tuning the N-glycosylation of recombinant human erythropoietin using Chlamydomonas reinhardtii mutants

Microalgae are considered as attractive expression systems for the production of biologics. As photosynthetic unicellular organisms, they do not require costly and complex media for growing and are able to secrete proteins and perform protein glycosylation. Some biologics have been successfully produced in the green microalgae Chlamydomonas reinhardtii. However, post-translational modifications like glycosylation of these Chlamydomonas-made biologics have poorly been investigated so far. Therefore, in this study, we report on the first structural investigation of glycans linked to human erythropoietin (hEPO) expressed in a wild-type C. reinhardtii strain and mutants impaired in key Golgi glycosyltransferases. The glycoproteomic analysis of recombinant hEPO (rhEPO) expressed in the wild-type strain demonstrated that the three N-glycosylation sites are 100% glycosylated with mature N-glycans containing four to five mannose residues and carrying core xylose, core fucose and O-methyl groups. Moreover, expression in C. reinhardtii insertional mutants defective in xylosyltransferases A and B and fucosyltransferase resulted in drastic decreases of core xylosylation and core fucosylation of glycans N-linked to the rhEPOs, thus demonstrating that this strategy offers perspectives for humanizing the N-glycosylation of the Chlamydomonas-made biologics.