The Irreversible Transport of Lipopolysaccharides.
In Gram-negative bacteria, lipopolysaccharides (LPS) LPSs are synthesized in the inner membrane, before being transported and assembled in the outer membrane1. the molecules are extracted from the external layer of the inner membrane and shuttled across a bridge to the outer membrane, before emerging on the cell surface. Two papers published in Nature now provide long-awaited details of the molecular processes that drive LPS transport.
The structures of six of the components of the LPS transport apparatus (made up of seven components) have been fully characterized. They reveal that a portal for LPS molecules forms two of the subunits in the outer membrane, and is connected to a pump in the inner membrane by a bridge, which includes other subunits.
The pump is driven by the binding and hydrolysis of cytoplasmic ATP, the cell’s energy-carrying molecule, but how it binds to LPSs from the inner membrane and pumps them only in the outward direction was unknown. The authors infer that the gate opens to allow LPS to slide past, but then spontaneously closes behind the molecule to block any backward flow.