Glycosylation in the crenarchaeon Sulfolobus solfataricus

Glycosylation is a complex process of co- or post-translational modification that expands the diversity of the proteome by the addition of different carbohydrate structures. Long believed to be an exclusively eukaryal trait, it is now clear that both Bacteria and Archaea are also capable of attaching glycan moieties to selected proteins. 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, much less is known of this post-translational modification in Archaea. Archaeal glycosylation displays bacterial-like and eukaryal-like traits, such as monomeric oligosyltransferases and dolichol phosphate carrier, respectively, in addition to unique features2. For instance, the oligosaccharide structure of cytochrome b558/566 from Sulfolobus acidocaldarius displays the presence of a rare acidic sugar, 6-sulfoquinovose (Qui6S)3, which has not been hitherto found in any other glycoprotein, although Qui6S is rather common in glycolipids of chloroplasts and photosynthetic bacteria4. Insights into the biosynthesis and attachment of N-linked glycans decorating archaeal glycoproteins arise from euryarchaeal model species, primarily halophiles5 and methanogenes6. In Crenarchaea, a phylum evolutionarily distant from Euryarchaea, the steps and the components of the synthesis of oligosaccharides of N-glycosylation have not been described to date. Here, we report our recent studies on the enzymes involved in the synthesis and in the maturation of the glycan component of the glycoproteins from the hyperthermophilic crenarchaeon Sulfolobus solfataricus7. A better understanding of archaeal glycosylation will provide new insights into this post-translational modification across evolution as well as protein processing under extreme conditions