Membrane proteins with beta-barrel fold

Porins, the major proteins found in the bacterial outer membrane, exhibit a n unusual hollow beta -barrel structure. This motif constitutes the scaffol d for a pore that facilitates the diffusion of solutes across the membrane. OmpF porin was the first membrane protein to be crystallized many years ag o at the Biozentrum in Basel. Since then a wealth of structural information at high resolution has been acquired by X-ray crystallography. Porins from E. coli turned out to be extremely robust and easy to manipulate, allowing detailed and comprehensive structure-function analysis. In particular, ins ight was obtained into the role of the highly charged pore constriction in OmpF porin and the 'greasy slide', a string of aromatic residues, in maltop orin.