FecB, a periplasmic ferric-citrate transporter from E. coli, can bind different forms of ferric-citrate as well as a wide variety of metal-free and metal-loaded tricarboxylic acids.

The Escherichia coli Fec system, consisting of an outer membrane receptor (FecA), a periplasmic substrate binding protein (FecB) and an inner membrane permease-ATPase type transporter (FecC/D), plays an important role in the uptake and transport of Fe(3+)-citrate. Although several FecB sequences from various organisms have been reported, there are no biophysical or structural data available for this protein to date. In this work, using isothermal titration calorimetry (ITC), we report for the first time the ability of FecB to bind different species of Fe(3+)-citrate as well as other citrate complexes with trivalent (Ga(3+), Al(3+), Sc(3+) and In(3+)) and a representative divalent metal ion (Mg(2+)) with low μM affinity.

The solution structure, binding properties, and dynamics of the bacterial siderophore-binding protein FepB.

The periplasmic binding protein (PBP) FepB plays a key role in transporting the catecholate siderophore ferric enterobactin from the outer to the inner membrane in Gram-negative bacteria. The solution structures of the 34-kDa apo- and holo-FepB from Escherichia coli, solved by NMR, represent the first solution structures determined for the type III class of PBPs. Unlike type I and II PBPs, which undergo large "Venus flytrap" conformational changes upon ligand binding, both forms of FepB maintain similar overall folds; however, binding of the ligand is accompanied by significant loop movements.

Role of the two structural domains from the periplasmic Escherichia coli histidine-binding protein HisJ.

Escherichia coli HisJ is a type II periplasmic binding protein that functions to reversibly capture histidine and transfer it to its cognate inner membrane ABC permease. Here, we used NMR spectroscopy to determine the structure of apo-HisJ (26.5 kDa) in solution.

A structural and functional analysis of type III periplasmic and substrate binding proteins: their role in bacterial siderophore and heme transport.

In Escherichia coli the Fhu, Fep and Fec transport systems are involved in the uptake of chelated ferric iron-siderophore complexes, whereas in pathogenic strains heme can also be used as an iron source. An essential step in these pathways is the movement of the ferric-siderophore complex or heme from the outer membrane transporter across the periplasm to the cognate cytoplasmic membrane ATP-dependent transporter. This is accomplished in each case by a dedicated periplasmic binding protein (PBP).

NMR solution structure and biophysical characterization of Vibrio harveyi acyl carrier protein A75H: effects of divalent metal ions.

Bacterial acyl carrier protein (ACP) is a highly anionic, 9 kDa protein that functions as a cofactor protein in fatty acid biosynthesis. Escherichia coli ACP is folded at neutral pH and in the absence of divalent cations, while Vibrio harveyi ACP, which is very similar at 86% sequence identity, is unfolded under the same conditions. V.

Siderophore uptake in bacteria and the battle for iron with the host; a bird's eye view.

Siderophores are biosynthetically produced and secreted by many bacteria, yeasts, fungi and plants, to scavenge for ferric iron (Fe(3+)). They are selective iron-chelators that have an extremely high affinity for binding this trivalent metal ion. The ferric ion is poorly soluble but it is the form of iron that is predominantly found in oxygenated environments.

A Novel extracytoplasmic function (ECF) sigma factor regulates virulence in Pseudomonas aeruginosa.

Next to the two-component and quorum sensing systems, cell-surface signaling (CSS) has been recently identified as an important regulatory system in Pseudomonas aeruginosa. CSS systems sense signals from outside the cell and transmit them into the cytoplasm. They generally consist of a TonB-dependent outer membrane receptor, a sigma factor regulator (or anti-sigma factor) in the cytoplasmic membrane, and an extracytoplasmic function (ECF) sigma factor.

Mutational study of the role of N-terminal amino acid residues in tetrachlorohydroquinone reductive dehalogenase from Sphingomonas sp. UG30.

This research presents the first extensive mutational study of N-terminal amino acids necessary for activity of a bacterial Zeta class glutathione transferase (GST). Our studies on UG30 tetrachlorohydroquinone reductive dehalogenase (PcpC) revealed that, similar to other Zeta class GSTs, N-terminal Ser and Cys residues play critical roles in glutathione binding and their mutation results in functional and structural changes to PcpC. Mutation of the N-terminal Ser and Cys residues decreased the apparent temperature optimum (by 6-10 degrees C) and maximum (by 5 degrees C) of PcpC.

Genetic improvement of Saccharomyces cerevisiae for xylose fermentation.

There is considerable interest in recent years in the bioconversion of forestry and agricultural residues into ethanol and value-added chemicals. High ethanol yields from lignocellulosic residues are dependent on efficient use of all the available sugars including glucose and xylose. The well-known fermentative yeast Saccharomyces cerevisiae is the preferred microorganism for ethanol production, but unfortunately, this yeast is unable to ferment xylose.

Bioinformatic analysis of the TonB protein family.

TonB is a protein prevalent in a large number of Gram-negative bacteria that is believed to be responsible for the energy transduction component in the import of ferric iron complexes and vitamin B(12) across the outer membrane. We have analyzed all the TonB proteins that are currently contained in the Entrez database and have identified nine different clusters based on its conserved 90-residue C-terminal domain amino acid sequence. The vast majority of the proteins contained a single predicted cytoplasmic transmembrane domain; however, nine of the TonB proteins encompass a approximately 290 amino acid N-terminal extension homologous to the MecR1 protein, which is composed of three additional predicted transmembrane helices.

Investigation of the role of a conserved glycine motif in the Saccharomyces cerevisiae xylose reductase.

All yeast xylose reductases, with the exception of that from Schizosaccharomyces pombe, possess the catalytic and coenzyme-binding elements from both the aldo-keto reductase and short-chain dehydrogenase-reductase (SDR) enzyme families in their primary sequences. In the Saccharomyces cerevisiae xylose reductase (XR), the SDR-like coenzyme-binding GXXXGXG motif (Gly motif) is located between residues 128 and 134, with the third Gly residue being replaced by an Asp. We used site-directed mutagenesis to study the role of this SDR-like Gly motif in the S.