Transmembrane ß-barrel proteins of bacteria: From structure to function.

ABSTRACT

The outer membrane of Gram-negative bacteria is a specialized organelle conferring protection to the cell against various environmental stresses and resistance to many harmful compounds. The outer membrane has a number of unique features, including an asymmetric lipid bilayer, the presence of lipopolysaccharides and an individual proteome. The vast majority of the integral transmembrane proteins in the outer membrane belongs to the family of ß-barrel proteins. These evolutionarily related proteins share a cylindrical, anti-parallel ß-sheet core fold spanning the outer membrane. The loops and accessory domains attached to the ß-barrel allow for a remarkable versatility in function for these proteins, ranging from diffusion pores and transporters to enzymes and adhesins. We summarize the current knowledge on ß-barrel structure and folding and give an overview of their functions, evolution, and potential as drug targets.