The structure of SAV1646 from Staphylococcus aureus belonging to a new `ribosome-associated' subfamily of bacterial proteins.

The crystal structure of the SAV1646 protein from the pathogenic microorganism Staphylococcus aureus has been determined at 1.7 Šresolution. The 106-amino-acid protein forms a two-layer sandwich with α/ß topology. The protein molecules associate as dimers in the crystal and in solution, with the monomers related by a pseudo-twofold rotation axis. A sequence-homology search identified the protein as a member of a new subfamily of yet uncharacterized bacterial `ribosome-associated' proteins with at least 13 members to date. A detailed analysis of the crystal protein structure along with the genomic structure of the operon containing the sav1646 gene allowed a tentative functional model of this protein to be proposed. The SAV1646 dimer is assumed to form a complex with ribosomal proteins L21 and L27 which could help to complete the assembly of the large subunit of the ribosome.

Mode of action, in vitro activity, and in vivo efficacy of AFN-1252, a selective antistaphylococcal FabI inhibitor.

The mechanism of action of AFN-1252, a selective inhibitor of Staphylococcus aureus enoyl-acyl carrier protein reductase (FabI), which is involved in fatty acid biosynthesis, was confirmed by using biochemistry, macromolecular synthesis, genetics, and cocrystallization of an AFN-1252-FabI complex. AFN-1252 demonstrated a low propensity for spontaneous resistance development and a time-dependent reduction of the viability of both methicillin-susceptible and methicillin-resistant S. aureus, achieving a ≥2-log(10) reduction in S. aureus counts over 24 h, and was extremely potent against clinical isolates of S. aureus (MIC(90), 0.015 µg/ml) and coagulase-negative staphylococci (MIC(90), 0.12 µg/ml), regardless of their drug resistance, hospital- or community-associated origin, or other clinical subgroup. AFN-1252 was orally available in mouse pharmacokinetic studies, and a single oral dose of 1 mg/kg AFN-1252 was efficacious in a mouse model of septicemia, providing 100% protection from an otherwise lethal peritoneal infection of S. aureus Smith. A median effective dose of 0.15 mg/kg indicated that AFN-1252 was 12 to 24 times more potent than linezolid in the model. These studies, demonstrating a selective mode of action, potent in vitro activity, and in vivo efficacy, support the continued investigation of AFN-1252 as a targeted therapeutic for staphylococcal infections.

Crystal structure of alkyl hydroperoxidase D like protein PA0269 from Pseudomonas aeruginosa: homology of the AhpD-like structural family.

BACKGROUND: Alkyl hydroperoxidase activity provides an important antioxidant defense for bacterial cells. The catalytic mechanism requires two peroxidases, AhpC and AhpD, where AhpD plays the role of an essential adaptor protein. RESULTS: The crystal structure of a putative AhpD from Pseudomonas aeruginosa has been determined at 1.9 Å. The protein has an all-helical fold with a chain topology similar to a known AhpD from Mycobacterium tuberculosis despite a low overall sequence identity of 9%. A conserved two α-helical motif responsible for function is present in both. However, in the P. aeruginosa protein, helices H3, H4 of this motif are located at the N-terminal part of the chain, while in M. tuberculosis AhpD, the corresponding helices H8, H9 are situated at the C-terminus. Residues 24-62 of the putative catalytic region of P. aeruginosa have a higher sequence identity of 33% where the functional activity is supplied by a proton relay system of five residues, Glu36, Cys48, Tyr50, Cys51, and His55, and one structural water molecule. A comparison of five other related hypothetical proteins from various species, assigned to the alkyl hydroperoxidase D-like protein family, shows they contain the same conserved structural motif and catalytic sequence Cys-X-X-Cys. We have shown that AhpD from P. aeruginosa exhibits a weak ability to reduce H(2)O(2) as tested using a ferrous oxidation-xylenol orange (FOX) assay, and this activity is blocked by thiol alkylating reagents. CONCLUSION: Thus, this hypothetical protein was assigned to the AhpD-like protein family with peroxidase-related activity. The functional relationship of specific oligomeric structures of AhpD-like structural family is discussed.

Structure of Francisella tularensis peptidyl-tRNA hydrolase.

The rational design of novel antibiotics for bacteria involves the identification of inhibitors for enzymes involved in essential biochemical pathways in cells. In this study, the cloning, expression, purification, crystallization and structure of the enzyme peptidyl-tRNA hydrolase from Francisella tularensis, the causative agent of tularemia, was performed. The structure of F. tularensis peptidyl-tRNA hydrolase is comparable to those of other bacterial peptidyl-tRNA hydrolases, with most residues in the active site conserved amongst the family. The resultant reagents, structural data and analyses provide essential information for the structure-based design of novel inhibitors for this class of proteins.

Ferric hydroxamate binding protein FhuD from Escherichia coli: mutants in conserved and non-conserved regions.

Uptake of iron complexes into the gram-negative bacterial cell requires highly specific outer membrane receptors and specific ATP-dependent (ATP-Binding-Cassette (ABC)) transport systems located in the inner membrane. The latter type of import system is characterized by a periplasmic binding protein (BP), integral membrane proteins, and membrane-associated ATP-hydrolyzing proteins. In gram-positive bacteria lacking the periplasmic space, the binding proteins are lipoproteins tethered to the cytoplasmic membrane. To date, there is little structural information about the components of ABC transport systems involved in iron complex transport. The recently determined structure of the Escherichia coli periplasmic ferric siderophore binding protein FhuD is unique for an ABC transport system (Clarke et al. 2000). Unlike other BP's, FhuD has two domains connected by a long alpha-helix. The ligand binds in a shallow pocket between the two domains. In vivo and in vitro analysis of single amino acid mutants of FhuD identified several residues that are important for proper functioning of the protein. In this study, the mutated residues were mapped to the protein structure to define special areas and specific amino acid residues in E. coli FhuD that are vital for correct protein function. A number of these important residues were localized in conserved regions according to a multiple sequence alignment of E. coli FhuD with other BP's that transport siderophores, heme, and vitamin B12. The alignment and structure prediction of these polypeptides indicate that they form a distinct family of periplasmic binding proteins.

X-ray crystallographic structures of the Escherichia coli periplasmic protein FhuD bound to hydroxamate-type siderophores and the antibiotic albomycin.

Siderophore-binding proteins play an essential role in the uptake of iron in many Gram-positive and Gram-negative bacteria. FhuD is an ATP-binding cassette-type (ABC-type) binding protein involved in the uptake of hydroxamate-type siderophores in Escherichia coli. Structures of FhuD complexed with the antibiotic albomycin, the fungal siderophore coprogen and the drug Desferal have been determined at high resolution by x-ray crystallography. FhuD has an unusual bilobal structure for a periplasmic ligand binding protein, with two mixed beta/alpha domains connected by a long alpha-helix. The binding site for hydroxamate-type ligands is composed of a shallow pocket that lies between these two domains. Recognition of siderophores primarily occurs through interactions between the iron-hydroxamate centers of each siderophore and the side chains of several key residues in the binding pocket. Rearrangements of side chains within the binding pocket accommodate the unique structural features of each siderophore. The backbones of the siderophores are not involved in any direct interactions with the protein, demonstrating how siderophores with considerable chemical and structural diversity can be bound by FhuD. For albomycin, which consists of an antibiotic group attached to a hydroxamate siderophore, electron density for the antibiotic portion was not observed. Therefore, this study provides a basis for the rational design of novel bacteriostatic agents, in the form of siderophore-antibiotic conjugates that can act as "Trojan horses," using the hydroxamate-type siderophore uptake system to actively deliver antibiotics directly into targeted pathogens.