Prescott's Microbiology 8th Edition by Joanne Willey, Linda Sherwood, Christopher J. Woolverton, Lansing Prescott, John Harley, Donald Klein

Exercise 5

Although the assembly of lipopolysaccharide (LPS) in gram-negative bacteria is well understood, its transport across and its insertion into the outer membrane remains unclear. It is known that lipid A attached to the core moiety is moved from the inner leaflet of the plasma membrane to the outer leaflet by a "flippase that resides in the membrane." Once in the periplasm, polymerized O-antigen units are attached to the lipid A core. Five candidate proteins, LptA, B, C, D, and E, were identified as essential team members responsible for ferrying the newly assembled LPS from the periplasm to the outer membrane. Where do you think these proteins are located within the cell or cell envelope to do this job? How do you think these proteins ensure that the orientation of the LPS in the outer membrane is correct? (Hint: It appears these proteins may work sequentially in time and space.)

Step 1 of 2

Assembly of lipopolysaccharide (LPS) requires the movement of its protein components across the inner membrane and outer membrane of the gram-negative bacteria cell wall. Sperandeo et al. has identified five proteins, LptABCDE, which help to bring the assembled LPS molecule across the cell wall.

The location for these proteins is near the either one of the two membranes. LptB is cytoplasmic but interacts with the inner membrane. LptF and LptG are believed to be in the inner membrane and interact with the MsbA inner membrane LPS transporter protein. LptA and LptC are periplasmic proteins that are thought to move LPS across the periplasm. LptD is lodged in the outer membrane and LptE is believed to be associated with it on the periplasmic side. LptD and LptE are involved in moving LPS across the outer membrane.