Shown are three systems in E. coli that facilitate removal of
mislocalized phospholipids from the outer leaflet. The OM phospholipase, PldA,
processively degrades mislocalized PLs. The Mla system is comprised of
components in each cellular compartment (MlaA,B,C,D,E,F) that collectively
facilitate retrograde PL trafficking. The palmitoyltransferase, PagP, also uses
mislocalized PLs as a substrate, and transfers an acyl chain to lipid A. The
resultant heptaacylated LPS contributes to OM stability and the lyso-PL
by-products can presumably be recycled.