Lipoproteins: Structure, Function, Biosynthesis

The Lpp lipoproteinof Escherichia coli is the first identified protein with a covalently linked lipid. It is chemically bound by its C-terminus to murein ( peptidoglycan) and inserts by the lipid at the N-terminus into the outer membrane. As the most abundant protein in E. coli (106 molecules per cell) it plays an important role for the integrity of the cell envelope. Lpp represents the type protein of a large variety of lipoproteinsfound in Gram-negative and Gram-positive bacteriaand in archaeathat have in common the lipid structure for anchoring the proteins to membranes but otherwise strongly vary in sequence, structure, and function. Predicted lipoproteinsin known prokaryotic genomes comprise 2.7% of all proteins. Lipoproteinsare modified by a unique phospholipid pathway and transferred from the cytoplasmic membrane into the outer membrane by a special system. They are involved in protein incorporation into the outer membrane, protein secretion across the cytoplasmic membrane, periplasm and outer membrane, signal transduction, conjugation, cell wall metabolism, antibiotic resistance, biofilm formation, and adhesion to host tissues. They are only found in bacteria and function as signal molecules for the innate immune systemof vertebrates, where they cause inflammation and elicit innate and adaptive immune response through Toll-like receptors. This review discusses various aspects of Lpp and other lipoproteinsof Gram-negative and Gram-positive bacteriaand archaea.