Prime Time for LipoPolySaccharides.
Two independent X-ray crystal structures of a lipid-polysaccharide transport (Lpt) protein machinery open the way to understand the detailed mechanism of LPS insertion in the outer-membrane, a fundamental feature of biological membranes that exhibit asymmetric distribution of the lipid membrane. The outer-membrane lipopolysaccharide comprises a lipid A membrane anchor, a core glycan unit, and a terminal O-carbohydrate chain. After being assembled in the cytoplasm, the lipopolysaccharide is transferred from the inner to the outer membrane as a result of the successive action of complexes involving in a time dependent manner seven proteins, LptA to LptE.
Both investigations deal with the so-called LptD-LptE protein complexes, from the bacteria Salmonella typhimurium and Shigella flexneri, respectively. They provide very detailed descriptions of the trajectory undergone by LPSs up to their final destination in the bacterial outer membrane. Beside deciphering a fundamental mechanism by which each complex transports around 5LPS molecules to the cell surface every second, these studies promise to facilitate the development of new antibiotics.