| Type: | Family | Name: | Ferrichrome-binding periplasmic protein |
| Description: | Iron is essential for growth in both bacteria and mammals. Controlling the amount of free iron in solution is often used as a tactic by hosts to limit invasion of pathogenic microbes; binding iron tightly within protein molecules can accomplish this. Such iron-protein complexes include haem in blood, lactoferrin in tears/saliva, and transferrin in blood plasma. Some bacteria express surface receptors to capture eukaryotic iron-binding compounds, while others have evolved siderophores (enterobactins) to scavenge iron from iron-binding host proteins []. Most high-affinity systems for iron uptake in Gram-negative bacteria are thought to employ periplasmic-binding-protein-dependent transport. In Escherichia coli, FepB is a periplasmic protein required for uptake of iron complexed to its endogenously-synthesized siderophore enterobactin (Ent) [].The control of such siderophore gene expression in E. coli is under the regulation of the negative repressor protein FUR []. When complexed with Fe2+, it down-regulates the transcription not only of the siderophore genes, but also of the moieties that release Fe2+ ions bound to the hydrox-amate enterobactin proteins in the microbial cytoplasm []. One of thesecodes for FhuD, a ferric hydroxymate binding protein located in the bacterial periplasm [, ]. Homologues of the FhuD gene, first described in E. coli, have been found in other Gram-negative pathogens, such as Yersinia pestisand Salmonella typhimurium, as well as in the plant microbe Rhizobium leguminosarum[, ].Recent mutational studies have shown the FhuD gene to be an essential and integral part of the ferric hydroxymate ABC transport system in E. coli []. Mutants lacking the Fhu operon were unable to utilise ferrichrome as an iron source, and showed a lower level of virulence than the wild type bacteria [].The structure of E. coli FhuD complexed to gallichrome has been resolved to 1.90A using X-ray crystallography []. The iron component is held in a shallow binding pocket between two domains separated by a long central alpha-helix []. This constitutes a novel fold, and is not found in any other periplasmic binding protein. | Short Name: | Ferrichrome-bd |
