Lipoproteins: Structure, Function, Biosynthesis

The Lpp lipoprotein of Escherichia coli is the first identified protein with a covalently linked lipidLipid. It is chemically boundChemical linkage by its C-terminus to mureinMurein (peptidoglycanPeptidoglycan) and inserts by the lipidLipid at the N-terminus into the outer membraneOuter membrane. As the most abundant protein in E. coli (106 molecules per cell) it plays an important role for the integrity of the cell envelopeCell envelope. Lpp represents the type protein of a large variety of lipoproteins found in Gram-negative and Gram-positive bacteriaGram-positive bacteria and in archaeaArchaea that have in common the lipidLipid structure for anchoring the proteins to membranes but otherwise strongly vary in sequence, structure, and function. Predicted lipoproteins in known prokaryotic genomes comprise 2.7% of all proteins. Lipoproteins are modified by a unique phospholipid pathway and transferred from the cytoplasmic membraneCytoplasmic membrane into the outer membraneOuter membrane by a special system. They are involved in protein incorporation into the outer membraneOuter membrane, protein secretionProtein secretion across the cytoplasmic membraneCytoplasmic membrane, periplasmPeriplasm and outer membraneOuter 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 system of vertebrates, where they cause inflammationInflammation and elicit innate and adaptive immune responseImmune response, adaptive, innate through Toll-like receptorsToll-like receptors. This review discusses various aspects of Lpp and other lipoproteins of Gram-negative and Gram-positive bacteriaGram-positive bacteria and archaeaArchaea.