The Escherichia coli AcrAB-TolC efflux pump is the archetype of the resistance nodulation cell division (RND) exporters from Gram-negative bacteria. Overexpression of RND-type efflux pumps is a major factor in multidrug resistance (MDR), which makes these pumps important antibacterial drug discovery targets. We have recently developed novel pyranopyridine-based inhibitors of AcrB, which are orders of magnitude more powerful than the previously known inhibitors. However, further development of such inhibitors has been hindered by the lack of structural information for rational drug design. Although only the soluble, periplasmic part of AcrB binds and exports the ligands, the presence of the membraneembedded domain in AcrB and its polyspecific binding behavior have made cocrystallization with drugs challenging. To overcome this obstacle, we have engineered and produced a soluble version of AcrB [AcrB periplasmic domain (AcrBper)], which is highly congruent in structure with the periplasmic part of the full-length protein, and is capable of binding substrates and potent inhibitors. Here, we describe the molecular basis for pyranopyridine-based inhibition of AcrB using a combination of cellular, X-ray crystallographic, and molecular dynamics (MD) simulations studies. The pyranopyridines bind within a phenylalanine-rich cage that branches from the deep binding pocket of AcrB, where they form extensive hydrophobic interactions. Moreover, the increasing potency of improved inhibitors correlates with the formation of a delicate protein-and water-mediated hydrogen bond network. These detailed insights provide a molecular platform for the development of novel combinational therapies using efflux pump inhibitors for combating multidrug resistant Gramnegative pathogens.RND efflux transporters | multidrug resistance | efflux pump inhibitors | X-ray crystallography | molecular dynamics simulation

Inflammation, regardless of whether it is provoked by infection or by tissue damage, starts with the activation of macrophages which initiate a cascade of inflammatory responses by producing the cytokines interleukin-1 (IL-1) and tumour necrosis factor-alpha (ref. 1). Three naturally occurring ligands for the IL-1 receptor (IL1R) exist: the agonists IL-1alpha and IL-1beta and the IL-1-receptor antagonist IL1RA (ref. 2). IL-1 is the only cytokine for which a naturally occurring antagonist is known. Here we describe the crystal structure at 2.7 A resolution of the soluble extracellular part of type-I IL1R complexed with IL1RA. The receptor consists of three immunoglobulin-like domains. Domains 1 and 2 are tightly linked, but domain three is completely separate and connected by a flexible linker. Residues of all three domains contact the antagonist and include the five critical IL1RA residues which were identified by site-directed mutagenesis. A region that is important for biological function in IL-1beta, the 'receptor trigger site' is not in direct contact with the receptor in the IL1RA complex. Modelling studies suggest that this IL-1beta trigger site might induce a movement of domain 3.

Respiratory syncytial virus (RSV) is a negative-sense, single-strand RNA virus that can initiate severe bronchiolitis in infants, as well as in elderly adults. Although RSV preferentially infects and replicates in the airway epithelium, studies have shown that RSV has the ability to infect and, to a limited extent, replicate in alveolar macrophages. In the present study, we sought to characterize the RSV-induced chemokine production in vitro and in vivo, because chemokines have been shown to contribute to both the inflammation and pathophysiology of disease. Our results show that RSV-infected airway epithelial cells and alveolar macrophages display differential profiles of chemokine production: airway epithelial cells produce CCL2/monocyte chemoattractant protein-1, CCL5/RANTES, CXCL10/gamma interferon inducible protein-10, and kerotinocyte cytokine (KC); and alveolar macrophages up-regulate CCL5 and macrophage inflammatory protein (MIP)-2 after RSV infection. In vivo, we observed the induction of CCL2, CCL3/MIP-1 alpha, CCL5, CXCL10, and KC after RSV infection. In the present study, we also addressed the necessity for viral infection and/or replication in chemokine induction by use of ultraviolet (UV)-inactivated RSV, as well as RSV inhibitors of binding/infection and replication, that is, NMSO3, a sulfated sialyl lipid compound, and ribavirin, respectively. Our results suggest that viral replication is necessary for optimal chemokine production.

cMembers of the resistance-nodulation-division (RND) family of efflux pumps, such as AcrAB-TolC of Escherichia coli, play major roles in multidrug resistance (MDR) in Gram-negative bacteria. A strategy for combating MDR is to develop efflux pump inhibitors (EPIs) for use in combination with an antibacterial agent. Here, we describe MBX2319, a novel pyranopyridine EPI with potent activity against RND efflux pumps of the Enterobacteriaceae. MBX2319 decreased the MICs of ciprofloxacin (CIP), levofloxacin, and piperacillin versus E. coli AB1157 by 2-, 4-, and 8-fold, respectively, but did not exhibit antibacterial activity alone and was not active against AcrAB-TolC-deficient strains. MBX2319 (3.13 M) in combination with 0.016 g/ml CIP (minimally bactericidal) decreased the viability (CFU/ml) of E. coli AB1157 by 10,000-fold after 4 h of exposure, in comparison with 0.016 g/ml CIP alone. In contrast, phenyl-arginine-␤-naphthylamide (PA␤N), a known EPI, did not increase the bactericidal activity of 0.016 g/ml CIP at concentrations as high as 100 M. MBX2319 increased intracellular accumulation of the fluorescent dye Hoechst 33342 in wild-type but not AcrAB-TolC-deficient strains and did not perturb the transmembrane proton gradient. MBX2319 was broadly active against Enterobacteriaceae species and Pseudomonas aeruginosa. MBX2319 is a potent EPI with possible utility as an adjunctive therapeutic agent for the treatment of infections caused by Gram-negative pathogens. Multidrug resistance (MDR) in Gram-negative pathogens, including Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter spp., and Stenotrophomonas maltophilia, poses a significant threat to the effective treatment of infections caused by these organisms (1-4). The MDR threat has been exacerbated by the recent decrease in commercial efforts to discover and develop new antibacterial agents. In addition, antibacterial agents that have been introduced recently into the clinic or are in development, such as daptomycin, gemifloxacin, telithromycin, and telavancin, are not active against Gram-negative pathogens. Recently FDAapproved agents with activity against Gram-negative bacteria include tigecycline and doripenem. While tigecycline is active against bacteria producing a tetracycline-specific pump in vitro, it is pumped out rapidly by the ubiquitous multidrug pumps, and its pharmacokinetic properties limit its use for treating urinary tract infections (UTIs) and bloodstream infections (5), as will the evolution of resistance during therapy (6). Clearly, novel strategies for effectively treating infections caused by MDR Gram-negative pathogens are urgently needed.The MDR phenotype has been attributed to both acquired and intrinsic mechanisms of resistance. However, the resistance-nodulation-division (RND) efflux pumps of Gram-negative bacteria play a major role in MDR. Because of their broad substrate specificity, overexpression of these efflux pumps results in decreased susceptibility to a diverse array of antibacterial agents and biocides (7). The major ef...

The type III secretion system (T3SS) is a clinically important virulence mechanism in Pseudomonas aeruginosa that secretes and translocates up to four protein toxin effectors into human cells, facilitating the establishment and dissemination of infections. To discover inhibitors of this important virulence mechanism, we developed two cellular reporter assays and applied them to a library of 80,000 compounds. The primary screen was based on the dependence of the transcription of T3SS operons on the T3SS-mediated secretion of a negative regulator and consisted of a transcriptional fusion of the Photorhabdus luminescens luxCDABE operon to the P. aeruginosa exoT effector gene. Secondary assays included direct measurements of the T3SS-mediated secretion of a P. aeruginosa ExoS effector-␤-lactamase fusion protein as well as the detection of the secretion of native ExoS by the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of culture supernatants. Five inhibitors in three chemical classes were demonstrated to inhibit type III secretion selectively with minimal cytotoxicity and with no effects on bacterial growth or on the type II-mediated secretion of elastase. These inhibitors also block the T3SS-mediated secretion of a YopE effector-␤-lactamase fusion protein from an attenuated Yersinia pestis strain. The most promising of the inhibitors is a phenoxyacetamide that also blocks the T3SS-mediated translocation of effectors into mammalian cells in culture. Preliminary studies of structure-activity relationships in this phenoxyacetamide series demonstrated a strict requirement for the R-enantiomer at its stereocenter and indicated tolerance for a variety of substituents on one of its two aromatic rings.The type-three secretion system (T3SS) is a complex multiprotein apparatus that facilitates the secretion and translocation of effector proteins from the bacterial cytoplasm directly into the mammalian cytosol. This complex protein delivery device is shared by more than 15 species of gram-negative human pathogens, including Salmonella spp., Shigella flexneri, Pseudomonas aeruginosa, Yersinia spp., enteropathogenic and enteroinvasive Escherichia coli, and Chlamydia spp. (23,25,43). In the opportunistic pathogen P. aeruginosa, the T3SS is the major virulence factor contributing to the establishment and dissemination of acute infections (19). Four T3SS effectors have been identified in P. aeruginosa strains: ExoS, ExoT, ExoY, and ExoU. ExoS and ExoT are bifunctional proteins consisting of an N-terminal small G-protein-activating protein (GAP) domain and a C-terminal ADP ribosylation domain, ExoY is an adenylate cyclase, and ExoU is a phospholipase (reviewed in reference 11). In studies with strains producing each effector separately, ExoU and ExoS contributed significantly to persistence, dissemination, and mortality, while ExoT produced minor effects on virulence in a mouse lung infection model, and ExoY did not appear to play a major role in the pathogenesis of P. aeruginosa (51). While not a p...