Structural basis of flagellar motility regulation by the MogR repressor and the GmaR antirepressor in Listeria monocytogenes.

The pathogenic Listeria monocytogenes bacterium produces the flagellum as a locomotive organelle at or below 30°C outside the host, but it halts flagellar expression at 37°C inside the human host to evade the flagellum-induced immune response. Listeria monocytogenes GmaR is a thermosensor protein that coordinates flagellar expression by binding the master transcriptional repressor of flagellar genes (MogR) in a temperature-responsive manner. To understand the regulatory mechanism whereby GmaR exerts the antirepression activity on flagellar expression, we performed structural and mutational analyses of the GmaR-MogR system. At or below 30°C, GmaR exists as a functional monomer and forms a circularly enclosed multidomain structure via an interdomain interaction. GmaR in this conformation recognizes MogR using the C-terminal antirepressor domain in a unique dual binding mode and mediates the antirepressor function through direct competition and spatial restraint mechanisms. Surprisingly, at 37°C, GmaR rapidly forms autologous aggregates that are deficient in MogR neutralization capabilities.

Crystal structure of the VanR transcription factor and the role of its unique α-helix in effector recognition.

VanR is a negative transcriptional regulator of bacteria that belongs to the PadR family and modulates the expression of vanillate transport and degradation proteins in response to vanillate. Although VanR plays a key role in the utilization of vanillate as a carbon source, it is barely understood how VanR recognizes its effector. Thus, our knowledge concerning the gene regulatory mechanism of VanR is limited. Here, we reveal the vanillate-binding mode of VanR through structural, biophysical, and mutational studies. Similar to other PadR family members, VanR forms a functional dimer, and each VanR subunit consists of an N-terminal DNA-binding domain (NTD) and a C-terminal dimerization domain (CTD). One VanR dimer simultaneously binds two vanillate molecules using two interdomain cavities, as observed in PadR. In contrast to these common features, VanR contains an additional α-helix, αi, that has not been found in other PadR family members. The αi helix functions as an interdomain crosslinker that mediates interactions between the NTD and the CTD. In addition, the VanR-specific αi helix plays a key role in the formation of a unique effector-binding site. As a result, the effector-binding mode of VanR is distinguishable from that of PadR in the location and accessibility of the effector-binding site as well as the orientation of its bound effector. Furthermore, we propose the DNA-binding mode and vanillate-mediated transcriptional regulation mechanism of VanR based on comparative structural and mutational analyses. DATABASES: The atomic coordinates and the structure factors for VanR (PDB ID 5Z7B) have been deposited in the Protein Data Bank, www.pdb.org.

Structural basis of effector and operator recognition by the phenolic acid-responsive transcriptional regulator PadR.

The PadR family is a large group of transcriptional regulators that function as environmental sensors. PadR negatively controls the expression of phenolic acid decarboxylase, which detoxifies harmful phenolic acids. To identify the mechanism by which PadR regulates phenolic acid-mediated gene expression, we performed structural and mutational studies of effector and operator recognition by Bacillus subtilis PadR. PadR contains an N-terminal winged helix-turn-helix (wHTH) domain (NTD) and a C-terminal homodimerization domain (CTD) and dimerizes into a dolmen shape. The PadR dimer interacts with the palindromic sequence of the operator DNA using the NTD. Two tyrosine residues and a positively charged residue in the NTD provide major DNA-binding energy and are highly conserved in the PadR family, suggesting that these three residues represent the canonical DNA-binding motif of the PadR family. PadR directly binds a phenolic acid effector molecule using a unique interdomain pocket created between the NTD and the CTD. Although the effector-binding site of PadR is positionally segregated from the DNA-binding site, effector binding to the interdomain pocket causes PadR to be rearranged into a DNA binding-incompatible conformer through an allosteric interdomain-reorganization mechanism.

Loeffler's Syndrome Induced by Ingestion of Urushiol Chicken.

Eosinophilic lung diseases are heterogeneous disorders characterized by varying degrees of pulmonary parenchyma or blood eosinophilia. Causes of eosinophilic lung diseases range from drug ingestion to parasitic or fungal infection as well as idiopathic. The exact pathogenesis of eosinophilic lung disease remains unknown. Urushiol chicken can frequently cause allergic reactions. Contact dermatitis (both local and systemic) represents the most-common side effect of urushiol chicken ingestion. However, there has been no previous report of lung involvement following urushiol chicken ingestion until now. A 66-year-old male was admitted to our hospital with exertional dyspnea. Serial chest X-ray revealed multiple migrating infiltrations in both lung fields, with eosinophilic infiltration revealed by lung biopsy. The patient had ingested urushiol chicken on two occasions within the 2 weeks immediately prior to disease onset. His symptoms and migrating lung lesions were resolved following administration of oral corticosteroids.