Figure 3.

Transport pathways of OM lipoproteins and LPS across the cell envelope in Gram-negative bacteria. OM lipoproteins and LPS are transported via a chaperone (Lol pathway) and protein bridge (Lpt machine), respectively. In Lol-mediated transport, ATP hydrolysis is only required to release lipoproteins from the IM. In Lpt-mediated LPS transport, ATP hydrolysis powers LPS transport all the way from the IM to the OM. Bulk PL transport from the IM to the OM depends on the pmf. As opposed to lipoprotein and LPS transport, PL transport across the envelope is bidirectional.