Structures and homologies of carbohydrate: phosphotransferase system (PTS) proteins

Abstract

The bacterial phosphotransferase system (PTS) is the major transport system for many carbohydrates that are phosphorylated concomitantly with the translocation step through the membrane (group translocation). It consists of two general proteins, enzyme I and histidine protein (HPr), and a series of more than 15 substrate-specific enzymes II (ElI). The sequences of several of these derived from Gram-positive and Gram-negative bacteria were compared, which allowed the possible identification of the following functional domains: membrane-bound pore, substrate-binding site, linker domains, transphosphorylation domain and primary phosphorylation site. Several Ells have been analysed in the meantime, also by topological .tests, by sequential deletion of the corresponding structural genes, and by construction of intergenic hybrids between different domains of several Ells. These data suggest evolutionary relationships between different Ells; they also enable a general model to be constructed of Ells as carbohydrate transport systems, phosphotransferases, chemoreceptors in chemotaxis and as part of a global regulatory network.