The structural analysis of the periplasmic domain of Sinorhizobium meliloti chemoreceptor McpZ reveals a novel fold and suggests a complex mechanism of transmembrane signaling.

Chemotaxis is a fundamental process whereby bacteria seek out nutrient sources and avoid harmful chemicals. For the symbiotic soil bacterium Sinorhizobium meliloti, the chemotaxis system also plays an essential role in the interaction with its legume host. The chemotactic signaling cascade is initiated through interactions of an attractant or repellent compound with chemoreceptors or methyl-accepting chemotaxis proteins (MCPs).

Biochemical analysis of protein-protein interfaces underlying the regulation of bacterial secretion systems.

Bacterial pathogens such as Pseudomonas aeruginosa use complex regulatory networks to tailor gene expression patterns to meet complex environmental challenges. P. aeruginosa is capable of causing both acute and chronic persistent infections, each type being characterized by distinct symptoms brought about by distinct sets of virulence mechanisms.

RetS inhibits Pseudomonas aeruginosa biofilm formation by disrupting the canonical histidine kinase dimerization interface of GacS.

Bacterial signaling histidine kinases (HKs) have long been postulated to function exclusively through linear signal transduction chains. However, several HKs have recently been shown to form complex multikinase networks (MKNs). The most prominent MKN, involving the enzymes RetS and GacS, controls the switch between the motile and biofilm lifestyles in the pathogenic bacterium Pseudomonas aeruginosa.

Backbone Interactions Between Transcriptional Activator ExsA and Anti-Activator ExsD Facilitate Regulation of the Type III Secretion System in Pseudomonas aeruginosa.

The type III secretion system (T3SS) is a pivotal virulence mechanism of many Gram-negative bacteria. During infection, the syringe-like T3SS injects cytotoxic proteins directly into the eukaryotic host cell cytoplasm. In Pseudomonas aeruginosa, expression of the T3SS is regulated by a signaling cascade involving the proteins ExsA, ExsC, ExsD, and ExsE.

Helix Cracking Regulates the Critical Interaction between RetS and GacS in Pseudomonas aeruginosa.

Recent paradigm shifting discoveries have demonstrated that bacterial signaling kinases engage in unexpected regulatory crosstalk, yet the underlying molecular mechanisms remain largely uncharacterized. The Pseudomonas aeruginosa RetS/GacS system constitutes an ideal model for studying these mechanisms. The in-depth analysis of the kinase region of RetS and RetS/GacS interactions presented here refutes a longstanding model, which posited the formation of a catalytically inactive RetS/GacS heterodimer.

Structure of the sensory domain of McpX from , the first known bacterial chemotactic sensor for quaternary ammonium compounds.

The α-proteobacterium can live freely in the soil or engage in a symbiosis with its legume host. facilitates nitrogen fixation in root nodules, thus providing pivotal, utilizable nitrogen to the host. The organism has eight chemoreceptors, namely McpT to McpZ and IcpA that facilitate chemotaxis.

The type IV pilus assembly ATPase PilB functions as a signaling protein to regulate exopolysaccharide production in Myxococcus xanthus.

Myxococcus xanthus possesses a form of surface motility powered by the retraction of the type IV pilus (T4P). Additionally, exopolysaccharide (EPS), the major constituent of bacterial biofilms, is required for this T4P-mediated motility in M. xanthus as the putative trigger of T4P retraction.

Using a Concept Inventory to Reveal Student Thinking Associated with Common Misconceptions about Antibiotic Resistance.

Misconceptions, also known as alternate conceptions, about key concepts often hinder the ability of students to learn new knowledge. Concept inventories (CIs) are designed to assess students' understanding of key concepts, especially those prone to misconceptions. Two-tiered CIs include prompts that ask students to explain the logic behind their answer choice.

Crystal Structure of a Type IV Pilus Assembly ATPase: Insights into the Molecular Mechanism of PilB from Thermus thermophilus.

Type IV pili (T4P) mediate bacterial motility and virulence. The PilB/GspE family ATPases power the assembly of T4P and type 2 secretion systems. We determined the structure of the ATPase region of PilB (PilB) in complex with ATPγS to provide a model of a T4P assembly ATPase and a view of a PilB/GspE family hexamer at better than 3-Å resolution.

Structural Analysis of the Regulatory Domain of ExsA, a Key Transcriptional Regulator of the Type Three Secretion System in Pseudomonas aeruginosa.

Pseudomonas aeruginosa employs a type three secretion system to facilitate infections in mammalian hosts. The operons encoding genes of structural components of the secretion machinery and associated virulence factors are all under the control of the AraC-type transcriptional activator protein, ExsA. ExsA belongs to a unique subfamily of AraC-proteins that is regulated through protein-protein contacts rather than small molecule ligands.

Self-association is required for occupation of adjacent binding sites in Pseudomonas aeruginosa type III secretion system promoters.

ExsA is a member of the AraC/XylS family of transcriptional regulators and is required for expression of the Pseudomonas aeruginosa type III secretion system (T3SS). All P. aeruginosa T3SS promoters contain two adjacent binding sites for monomeric ExsA.

A naturally variable residue in the S1 subsite of M1 family aminopeptidases modulates catalytic properties and promotes functional specialization.

M1 family metallo-aminopeptidases fulfill a wide range of critical and in some cases medically relevant roles in humans and human pathogens. The specificity of M1-aminopeptidases is dominated by the interaction of the well defined S1 subsite with the side chain of the first (P1) residue of the substrate and can vary widely. Extensive natural variation occurs at one of the residues that contributes to formation of the cylindrical S1 subsite.

Self-trimerization of ExsD limits inhibition of the Pseudomonas aeruginosa transcriptional activator ExsA in vitro.

The opportunistic pathogen Pseudomonas aeruginosa ranks among the leading causes of nosocomial infection. The type III secretion system (T3SS) aids acute Pseudomonas aeruginosa infection by injecting potent cytotoxins into host cells to suppress the host's innate immune response. Expression of all T3SS-related genes is strictly dependent on the transcription factor ExsA.

The catalytic domain of the germination-specific lytic transglycosylase SleB from Bacillus anthracis displays a unique active site topology.

Bacillus anthracis produces metabolically inactive spores. Germination of these spores requires germination-specific lytic enzymes (GSLEs) that degrade the unique cortex peptidoglycan to permit resumption of metabolic activity and outgrowth. We report the first crystal structure of the catalytic domain of a GSLE, SleB.

Orientation of Pseudomonas aeruginosa ExsA monomers bound to promoter DNA and base-specific contacts with the P(exoT) promoter.

ExsA is a transcriptional activator of the Pseudomonas aeruginosa type III secretion system (T3SS) and a member of the AraC/XylS protein family. Each of the 10 ExsA-dependent promoter regions that define the T3SS regulon has two adjacent binding sites for monomeric ExsA. Whereas the promoter-proximal sites (binding site 1) contain highly conserved GnC and TGnnA sequences that are separated by ∼10 bp, the promoter-distal sites (binding site 2) share no obvious sequence similarity to each other or to the binding site 1 consensus.

Phosphorylation and dephosphorylation among Dif chemosensory proteins essential for exopolysaccharide regulation in Myxococcus xanthus.

Myxococcus xanthus social gliding motility, which is powered by type IV pili, requires the presence of exopolysaccharides (EPS) on the cell surface. The Dif chemosensory system is essential for the regulation of EPS production. It was demonstrated previously that DifA (methyl-accepting chemotaxis protein [MCP]-like), DifC (CheW-like), and DifE (CheA-like) stimulate whereas DifD (CheY-like) and DifG (CheC-like) inhibit EPS production.

Analysis of the crystal structure of the ExsC.ExsE complex reveals distinctive binding interactions of the Pseudomonas aeruginosa type III secretion chaperone ExsC with ExsE and ExsD.

Pseudomonas aeruginosa, like many Gram-negative bacterial pathogens, requires its type III secretion system (T3SS) to facilitate acute infections. In P. aeruginosa, the expression of all T3SS-related genes is regulated by the transcriptional activator ExsA.

Crystal structure and oligomeric state of the RetS signaling kinase sensory domain.

The opportunistic pathogen Pseudomonas aeruginosa may cause both acute and chronic-persistent infections in predisposed individuals. Acute infections require the presence of a functional type III secretion system (T3SS), whereas chronic P. aeruginosa infections are characterized by the formation of drug-resistant biofilms.

Structural evidence suggests that antiactivator ExsD from Pseudomonas aeruginosa is a DNA binding protein.

The opportunistic pathogen P. aeruginosa utilizes a type III secretion system (T3SS) to support acute infections in predisposed individuals. In this bacterium, expression of all T3SS-related genes is dependent on the AraC-type transcriptional activator ExsA.

New protein fold revealed by a 1.65 A resolution crystal structure of Francisella tularensis pathogenicity island protein IglC.

Francisella tularensis is a highly infectious Gram-negative intracellular pathogen that causes the fulminating disease tularemia and is considered to be a potential bioweapon. F. tularensis pathogenicity island proteins play a key role in modulating phagosome biogenesis and subsequent bacterial escape into the cytoplasm of macrophages.

Structure of the POZ domain of human LRF, a master regulator of oncogenesis.

The proto-oncogenic properties of the POK family of transcriptional repressors BCL6, PLZF, and LRF have been well established. These proteins utilize their amino-terminal POZ domains for multimerization and the recruitment of co-repressors. Because LRF represses the production of the tumor suppressor p19(Arf) (ARF), it is regarded as an attractive therapeutic target for the treatment of many types of cancer.

Selection and characterization of Yersinia pestis YopN mutants that constitutively block Yop secretion.

Secretion of Yop effector proteins by the Yersinia pestis plasmid pCD1-encoded type III secretion system (T3SS) is regulated in response to specific environmental signals. Yop secretion is activated by contact with a eukaryotic cell or by growth at 37 degrees C in the absence of calcium. The secreted YopN protein, the SycN/YscB chaperone and TyeA form a cytosolic YopN/SycN/YscB/TyeA complex that is required to prevent Yop secretion in the presence of calcium and prior to contact with a eukaryotic cell.

Crystal structure of the protease-resistant core domain of Yersinia pestis virulence factor YopR.

Yersinia pestis, the causative agent of the plague, employs a type III secretion system (T3SS) to secrete and translocate virulence factors into to the cytoplasm of mammalian host cells. One of the secreted virulence factors is YopR. Little is known about the function of YopR other than that it is secreted into the extracellular milieu during the early stages of infection and that it contributes to virulence.

Three-dimensional structure of a macromolecular assembly that regulates type III secretion in Yersinia pestis.

Yersinia pestis, the causative agent of plague, utilizes a type III secretion system (T3SS) to inject effector proteins directly into the cytosol of mammalian cells where they interfere with signal transduction pathways that regulate actin cytoskeleton dynamics and inflammation, thereby enabling the bacterium to avoid engulfment and destruction by macrophages. Type III secretion normally does not occur in the absence of close contact with eukaryotic cells. Negative regulation is mediated in part by a multiprotein complex that has been proposed to act as a physical impediment to type III secretion by blocking the entrance to the secretion apparatus prior to contact with mammalian cells.

On increasing protein-crystallization throughput for X-ray diffraction studies.

Two recent developments, a novel screening/optimization strategy that considerably reduces the number of trials required to produce diffraction-size crystals and a simple modification that doubles the screening capacity of the Douglas Instruments ORYX 1-6 protein-crystallization robot, have been implemented into a structural genomics project. The new two-step screening/optimization strategy yields diffraction-quality crystals directly from the screening process, reducing the need for further optimization. The ORYX modification involves the addition of extensions to the sample- and oil-delivery arms and software modifications that allow two plates to be set up simultaneously.