Archaeal glycosylation: analysis of the glycome and identification of the enzymes involved

Glycosylation is one of the most prevalent post-translational modifications of proteins that expand the diversity of the proteome by the addition of different glycan moieties. Long believed a prerogative of eukaryotes, it is now clear that both N-glycosylation and O-glycosylation also transpire in Bacteria and Archaea. In recent years, substantial progresses are being made in understanding bacterial glycosylation while much less is known of this post-translational modification in Archaea, despite the fact that the first prokaryotic N-glycosylated protein was discovered over three decades ago in the haloarchaeon Halobacterium salinarum1 and that N-glycosylated proteins are more prevalent in Archaea than in Bacteria. Archaeal glycosylation displays bacterial- and eukaryal-like traits, such as monomeric oligosyltransferases and dolichol phosphate carrier respectively, in addition to unique features2. Insights into the biosynthesis and the nature of N-linked glycans decorating archaeal glycoproteins arise from euryarchaeal model species3. In Crenarchaea, a phylum evolutionarily distant from Euryarchaea, the study of the steps and the components of the machinery involved in glycosylation and of the nature of the glycosylated proteins is still in its infancy. However, preliminary results indicate that glycosylation in these organisms is indispensable for cell survival4 and even more widespread than in Euryarchaea5. Here, we report our recent studies on the enzymes from the hyperthermophilic crenarchaeon Sulfolobus solfataricus involved in the synthesis and in the maturation of the glycan component of the glycoproteins6. Moreover, sugar composition and structure of the sulfolobales glycoproteins are explored by glycoproteomic analysis. A better understanding of crenarchaeal glycosylation will provide new insights into this post-translational modification across evolution as well as protein processing under extreme conditions.