Lipopolysaccharide transport and assembly at the outer membrane: the PEZ model

Abstract

Gram-negative bacteria contain a double-membrane cellular envelope that enables them to colonize harsh environments and prevents entry of many clinically available antibiotics. A main component of most outer membranes is lipopolysaccharide (LPS), a glycolipid containing multiple fatty acyl chains and up to hundreds of sugars that is synthesized in the cytoplasm. In the last two decades, the proteins responsible for transporting LPS across the cellular envelope and assembling it at the cell surface in Escherichia coli have been identified, but it remains unclear how they function. In this Review, we discuss recent advances in this area and present a model explaining how energy from the cytoplasm is used to power LPS transport across the cellular envelope to the cell surface.