Exploring protein N-glycosylation in the green microalga Dunaliella salina

N -glycosylation is a major post-translational modification of proteins that has a crucial influence on cell targeting, activity, and half-life. This process starts in the endoplasmic reticulum where an oligosaccharide precursor is added to the newly synthesized protein and continues in the Golgi apparatus where the N -linked carbohydrate sequences are processed. Importantly, the most approved recombinant pharmaceutical proteins (so-called biologics) are glycoproteins mainly currently produced in mammalian cells which is a lengthy, costly, and complex process. Today, several microalgae such as the diatom Phaeodactylum tricornutum , and the green microalgae Chlamydomonas reinhardtii , Chlorella vulgaris , and Dunaliella salina are considered as efficient and eco-friendly alternative platforms for the production of biologics. However, unlike for C. reinhardtii , C. vulgaris , and P. tricornutum , there is to date no data reported regarding the protein N -glycosylation pathway in D. salina . Here, we first investigated the protein N -glycosylation in this green microalga by MALDI-TOF mass spectrometry. These analyses showed that proteins from D. salina are N -glycosylated with Man 5 GlcNAc 2 oligomannoside. Using genome mining approaches, we then identified genes encoding proteins involved in the N -glycosylation pathways in D. salina . Genetic similarities and phylogenetic relationships of the putative sequences with homologues from C. reinhardtii , P. tricornutum , and humans were investigated. These data revealed that in D. salina the biosynthesis of nucleotide sugars and N -glycan biosynthesis share mainly similarities with the GnT I-independent pathway of C. reinhardtii that gives rise to the synthesis of a non-canonical oligomannoside Man 5 GlcNAc 2 . Although an α(1,3)-fucosyltransferase is identified in the D. salina genome, impairment of the cytosolic GDP-Fuc biosynthesis prevents the Golgi fucosylation of N -glycans. Taken together, these data demonstrated that proteins from D. salina are homogeneously N -glycosylated with a non-canonical Man 5 GlcNAc 2 . • The N -glycosylation pathway in D. salina is independent of the GnT I enzyme. • No fucose and xylose residues exist in the glycoproteins of D. salina . • D. salina is a safer platform for the production of pharmaceutical glycoproteins.