Periplasmic Transport Systems Research Articles

Escherichia coli K-12 envelope proteins specifically required for ferrienterobactin uptake.

Escherichia coli genes specifically required for transport of iron by the siderophore enterobactin are designated fep. The studies reported here were initiated to identify and localize the fepB product. The plasmid pCP111, which consisted of an 11-kilobase E. coli DNA fragment containing fepB ligated to pACYC184, was constructed. The fepB gene was subcloned; in the process, complementation tests and Tn5 mutagenesis results provided evidence for the existence of a new fep gene, fepC. The order of the transport genes in the ent gene cluster is as follows: fepA fes entF fepC fepB entE. Minicell, maxicell, and in vitro DNA-directed protein synthesizing systems were used to identify the fepB and fepC products. The fepC polypeptide was 30,500 daltons in standard sodium dodecyl sulfate-polyacrylamide gels. The fepB gene was responsible for the appearance of three or four bands (their apparent molecular weights ranged from 31,500 to 36,500) in sodium dodecyl sulfate-polyacrylamide gels, depending on the gel system employed. The largest of these was tentatively designated proFepB, since it apparently had a leader sequence. Localization experiments showed that FepC was a membrane constituent and that mature FepB was present in the periplasm. An additional polypeptide (X) was also encoded by the bacterial DNA of pCP111, but its relationship to iron transport is unknown. The results indicated that ferrienterobactin uptake is mediated by a periplasmic transport system and that genes coding for outer membrane (fepA), periplasmic (fepB), and cytoplasmic membrane (fepC) components have now been identified.

Bacterial periplasmic transport systems: structure, mechanism, and evolution.

Bacterial periplasmic transport systems: structure, mechanism, and evolution.

Bacterial Periplasmic Transport Systems: Structure, Mechanism, and Evolution

Bacterial Periplasmic Transport Systems: Structure, Mechanism, and Evolution

ATP-binding sites in the membrane components of histidine permease, a periplasmic transport system.

Two components of the histidine permease in Salmonella typhimurium, the membrane-bound P and M proteins, react with the photoaffinity labeling reagent 8-azido-ATP in isolated membranes. The extent of labeling is decreased by the addition of ATP and somewhat less by addition of GTP, CTP, UTP, and ADP. Cyclic AMP, NAD, FAD, and S-adenosylmethionine have little effect. We propose that one or both of these proteins have a site capable of binding an adenine nucleotide and that, therefore, they may be involved in the energy-coupling step in active transport.

Molecular mechanisms of bacterial periplasmic transport systems.

Molecular mechanisms of bacterial periplasmic transport systems.

The organization, mechanism of action, and evolution of periplasmic transport systems

Recent advances in molecular genetic techniques are now beginning to shed some light on the molecular mechanisms by which metabolites are transported across bacterial membranes and the role of periplasmic binding proteins in these processes. A comparison of such complex systems is providing some new insights into their evolutionary development.