3.A.1.106.15
Lipid flippase, PglK or WlaB, of 564 aas and 6 N-terminal TMSs with a C-terminal ATPase domain.  Mediates the ATP-dependent translocation of an undecaprenylpyrophosphate-linked heptasaccharide intermediate (LLO) across the cell membrane, an essential step during the N-linked protein glycosylation pathway. Transport across the membrane is effected via ATP-driven conformation changes. Most likely, only the polar and charged part of the glycolipid enter the substrate-binding cavity, and the lipid tail remains exposed to the membrane lipids during the transmembrane flipping process (Alaimo et al. 2006; Kelly et al. 2006; Perez et al. 2015). PglK may employ a "substrate-hunting" mechanism to locally increase the LLO concentration and facilitate its jump into the translocation pathway, for which sugars from the LLO head group are essential; the release of LLO to the outside occurs before ATP hydrolysis and is followed by the closing of the periplasmic cavity of PglK (Perez et al. 2019). The bacterial lipid-linked oligosaccharide (LLO) flippase, PglK, in which the hydrophilic head group and the hydrophobic polyprenyl tail of the substrate are proposed to have distinct translocation pathways but are not chemically separated during transport (Theodoulou et al. 2016).