Different routes to the same ending: comparing the N‐glycosylation processes of Haloferax volcanii and Haloarcula marismortui , two halophilic archaea from the Dead Sea

Summary Recent insight into the N‐glycosylation pathway of the haloarchaeon, Haloferax volcanii , is helping to bridge the gap between our limited understanding of the archaeal version of this universal post‐translational modification and the better‐described eukaryal and bacterial processes. To delineate as yet undefined steps of the Hfx. volcanii N‐glycosylation pathway, a comparative approach was taken with the initial characterization of N‐glycosylation in Haloarcula marismortui , a second haloarchaeon also originating from the Dead Sea. While both species decorate the reporter glycoprotein, the S‐layer glycoprotein, with the same N‐linked pentasaccharide and employ dolichol phosphate as lipid glycan carrier, species‐specific differences in the two N‐glycosylation pathways exist. Specifically, Har. marismortui first assembles the complete pentasaccharide on dolichol phosphate and only then transfers the glycan to the target protein, as in the bacterial N‐glycosylation pathway. In contrast, Hfx. volcanii initially transfers the first four pentasaccharide subunits from a common dolichol phosphate carrier to the target protein and only then delivers the final pentasaccharide subunit from a distinct dolichol phosphate to the N‐linked tetrasaccharide, reminiscent of what occurs in eukaryal N‐glycosylation. This study further indicates the extraordinary diversity of N‐glycosylation pathways in Archaea, as compared with the relatively conserved parallel processes in Eukarya and Bacteria.