Bacterial Periplasmic Permeases as Model Systems for the Superfamily of Traffic ATPases, Including the Multidrug Resistance Protein and the Cystic Fibrosis Transmembrane Conductance Regulator

Abstract

This chapter discusses the composition and basic features of periplasmic permeases of gram-negative bacteria emphasizing those aspects of periplasmic transport that relate to their energy-coupling mechanism and structural organization. The mechanism of action of eukaryotic transporters is also presented in the chapter. Periplasmic permeases are composed of a receptor (a periplasmic substrate binding protein) and two to three membrane-bound components. All periplasmic permeases have the same overall composition. The similarity in the composition of these permeases indicates a conserved structural organization and mechanism of action despite the vast variety of substrates transported and a common evolutionary origin. Periplasmic permeases typically concentrate substrates against a very large concentration gradient. ATP binding and hydrolysis result in the conformational changes that are transmitted to the rest of the permease, thereby causing the opening of a pore or the creation of a substrate binding site in the membrane-bound complex. Conformational changes may be necessary as a signal for the receptor to release the substrate, which is deeply buried between its two lobes.