3.A.1.106.20
MsbA of 582 aas and 6 TMSs in an M-C arrangement.  The X-ray structure at 2.8 Å resolution in an inward-facing conformation after cocrystallization with lipid A and using a stabilizing facial amphiphile has been reported (Padayatti et al. 2019). The structure displays a large amplitude opening in the transmembrane portal, which is likely to be required for lipid A to pass from its site of synthesis into the protein-enclosed transport pathway. Putative lipid A density is observed further inside the transmembrane cavity, consistent with a trap and flip model. Additional electron density attributed to lipid A is observed near an outer surface cleft at the periplasmic ends of the transmembrane helices (Padayatti et al. 2019). This protein is 96% identical to the E. coli ortholog, TC# 3.A.1.106.1.