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).