The YebST system (renamed the LetAB system) of intermembrane phospholipid translocation (Nakayama and Zhang-Akiyama 2016). LetA is a 427 aa protein with 8 TMSs in the cytoplasmic membrane while LetB  is an 877 aa protein; it spans the periplasm and has an N-terminal TMS followed by seven repeats that are stacked on top of each other to form a channel across the periplasm. The first repeat accepts the phospholipid from LetA while the seventh repeat interacts with the outer membrane where it delivers the phospholipid (Isom et al. 2020).