Figure 2: Model for LPS transport by the Lpt system.

LPS is transported from the inner membrane (IM) to the outer membrane (OM) by the LptB₂FGCADE complex in an ATP-dependent manner. Each round of ATP binding and hydrolysis by the LptB₂FGC ABC transporter is thought to be used to extract one molecule of LPS from the inner membrane and place it onto the periplasmic Lpt bridge. Repeated rounds of hydrolysis extract LPS molecules that push others ahead on the bridge so that a stream of LPS travels towards the outer membrane through the Lpt bridge. LPS finally reaches the LptDE translocon and exits into the outer leaflet of the outer membrane. PG represents the peptidoglycan cell wall.