Fig. 1

Basic components of the polyisoprenol-based machineries. a Typical polyisoprenol lipid carriers in the three domains of life. b Topology (membrane orientation) of characteristic N-glycosylation pathways in the three domains of life and bacterial peptidoglycan biosynthesis. The lipid carrier is embedded in a cell membrane (ER membrane in eukaryotes, plasma membranes in archaea and bacteria), first facing the cytoplasmic side, then flipped to the opposite side (i.e. ER lumen in eukaryotes, periplasm in prokaryotes). Monosaccharides are attached one by one to the lipid carriers by specific glycosyltransferases, although in the eukaryotic N-glycosylation each kind of sugar is only represented once per compartment, for simplicity. The monosaccharides are nucleotide-activated in the cytoplasmic side or translocated to the ER lumen by separate lipid carriers