Search

The Helicobacter pylori adhesin BabA binds mucosal ABO/Le(b) blood group (bg) carbohydrates. BabA facilitates bacterial attachment to gastric surfaces, increasing strain virulence and forming a recognized risk factor for peptic ulcers and gastric cancer. High sequence variation causes BabA functional diversity, but the underlying structural-molecular determinants are unknown. We generated X-ray structures of representative BabA isoforms that reveal a polymorphic, three-pronged Le(b) binding site. Two diversity loops, DL1 and DL2, provide adaptive control to binding affinity, notably ABO versus O bg preference. H. pylori strains can switch bg preference with single DL1 amino acid substitutions, and can coexpress functionally divergent BabA isoforms. The anchor point for receptor binding is the embrace of an ABO fucose residue by a disulfide-clasped loop, which is inactivated by reduction. Treatment with the redox-active pharmaceutic N-acetylcysteine lowers gastric mucosal neutrophil infiltration in H. pylori-infected Le(b)-expressing mice, providing perspectives on possible H. pylori eradication therapies.

During the different stages of the Plasmodium life cycle, surface-associated proteins establish key interactions with the host and play critical roles in parasite survival. The 6-cysteine (6-cys) protein family is one of the most abundant surface antigens and expressed throughout the Plasmodium falciparum life cycle. This protein family is conserved across Plasmodium species and plays critical roles in parasite transmission, evasion of the host immune response and host cell invasion. Several 6-cys proteins are present on the parasite surface as hetero-complexes but it is not known how two 6-cys proteins interact together. Here, we present a crystal structure of Pf12 bound to Pf41 at 2.85 Å resolution, two P. falciparum proteins usually found on the parasite surface of late schizonts and merozoites. Our structure revealed two critical interfaces required for complex formation with important implications on how different 6-cysteine proteins may interact with each other. Using structure-function analyses, we identified important residues for Pf12-Pf41 complex formation. In addition, we generated 16 nanobodies against Pf12 and Pf41 and showed that several Pf12-specific nanobodies inhibit Pf12-Pf41 complex formation. Using X-ray crystallography, we were able to describe the structural mechanism of an inhibitory nanobody in blocking Pf12-Pf41 complex formation. Future studies using these inhibitory nanobodies will be useful to determine the functional role of these two 6-cys proteins in malaria parasites. [ABSTRACT FROM AUTHOR]

Abstract Background Porphyromonas gingivalis in subgingival dental plaque, as part of a mature biofilm, has been strongly implicated in the onset and progression of chronic periodontitis. In this study using DNA microarray we compared the global gene expression of a P. gingivalis biofilm with that of its planktonic counterpart grown in the same continuous culture. Results Approximately 18% (377 genes, at 1.5 fold or more, P-value < 0.01) of the P. gingivalis genome was differentially expressed when the bacterium was grown as a biofilm. Genes that were down-regulated in biofilm cells, relative to planktonic cells, included those involved in cell envelope biogenesis, DNA replication, energy production and biosynthesis of cofactors, prosthetic groups and carriers. A number of genes encoding transport and binding proteins were up-regulated in P. gingivalis biofilm cells. Several genes predicted to encode proteins involved in signal transduction and transcriptional regulation were differentially regulated and may be important in the regulation of biofilm growth. Conclusion This study analyzing global gene expression provides insight into the adaptive response of P. gingivalis to biofilm growth, in particular showing a down regulation of genes involved in growth and metabolic activity.

Bacterial autotransporters comprise a C-terminal β-barrel domain, which must be correctly folded and inserted into the outer membrane to facilitate translocation of the N-terminal passenger domain to the cell exterior. Once at the surface, the passenger domains of most autotransporters are folded into an elongated β-helix. In a cellular context, key molecules catalyze the assembly of the autotransporter β-barrel domain. However, how the passenger domain folds into its functional form is poorly understood. Here we use mutational analysis on the autotransporter Pet to show that the β-hairpin structure of the fifth extracellular loop of the β-barrel domain has a crucial role for passenger domain folding into a β-helix. Bioinformatics and structural analyses, and mutagenesis of a homologous autotransporter, suggest that this function is conserved among autotransporter proteins with β-helical passenger domains. We propose that the autotransporter β-barrel domain is a folding vector that nucleates folding of the passenger domain. [ABSTRACT FROM AUTHOR]

Objectives: Escherichia coli ST131 is a globally disseminated MDR clone originally identified due to its association with the blaCTX-M-15 gene encoding an ESBL. It is thus assumed that blaCTX-M-15 is the major determinant for resistance to β-lactam antibiotics in this clone. The complete sequence of EC958, a reference strain for E. coli ST131, revealed that it contains a chromosomally located blaCMY-M-23 gene with an upstream ISEcp1 element as well as several additional plasmid-encoded β-lactamase genes. Here, we examined the genetic context of the blaCMY-M-23 element in EC958 and other E. coli ST131 strains and investigated the contribution of blaCMY-M-23 to EC958 resistance to a range of β-lactam antibiotics. Methods: The genetic context of blaCMY-M-23 and its associated mobile elements was determined by PCR and sequencing. Antibiotic susceptibility testing was performed using Etests. The activity of the blaCMY-M-23 promoter was assessed using lacZ reporter assays. Mutations were generated using λ-Red-recombination. Results: The genetic structure of the ISEcp1-IS5-blaCTX-M-23 mobile element was determined and localized within the betU gene on the chromosome of EC958 and five other E. coli ST131 strains. The transcription of blaCTX-M-23, driven by a previously defined promoter within ISEcp1, was significantly higher than other β-lactamase genes and could be induced by cefotaxime. Deletion of the blaCTX-M-23 gene resulted in enhanced susceptibility to cefoxitin, cefotaxime and ceftazidime. Conclusions: This is the first known report to demonstrate the chromosomal location of blaCTX-M-23 in E. coli ST131. In EC958, CMY-23 plays a major role in resistance to third-generation cephalosporins and cephamycins. [ABSTRACT FROM AUTHOR]

Shiga toxin Stx2e is the major known agent that causes edema disease in newly weaned pigs. This severe disease is characterized by neurological disorders, hemorrhagic lesions, and frequent fatal outcomes. Stx2e consists of an enzymatically active A subunit and five B subunits that bind to a specific glycolipid receptor on host cells. It is evident that antibodies binding to the A subunit or the B subunits of Shiga toxin variants may have the capability to inhibit their cytotoxicity. Here, we report the discovery and characterization of a VHH single domain antibody (nanobody) isolated from a llama phage display library that confers potent neutralizing capacity against Stx2e toxin.Wefurther present the crystal structure of the complex formed between the nanobody (NbStx2e1) and the Stx2e toxoid, determined at 2.8Å resolution. Structural analysis revealed that for each B subunit of Stx2e, one NbStx2e1 is interacting in a head-to-head orientation and directly competing with the glycolipid receptor binding site on the surface of the B subunit. The neutralizing NbStx2e1 can in the future be used to prevent or treat edema disease. [ABSTRACT FROM AUTHOR]

Bacteria express a multitude of hair-like adhesive appendages on their cell surfaces, together referred to as pili or fimbriae. In Gram-negative bacteria, these proteinaceous structures are assembled through a number of dedicated secretion pathways including the chaperone-usher pathway, the nucleation/precipitation pathway and the type IV pilus pathway. Pili are prevalent in pathogenic strains and play important roles in the establishment and persistence of bacterial infections by mediating host cell adhesion, cell invasion or biofilm formation. Their indispensible roles in pathogenesis render them attractive targets for directed therapeutic intervention. Here, we describe the recent advances in the chemical attenuation of pilus-associated virulence in Gram-negative bacteria., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Background: Porphyromonas gingivalis in subgingival dental plaque, as part of a mature biofilm, has been strongly implicated in the onset and progression of chronic periodontitis. In this study using DNA microarray we compared the global gene expression of a P. gingivalis biofilm with that of its planktonic counterpart grown in the same continuous culture., Results: Approximately 18% (377 genes, at 1.5 fold or more, P-value < 0.01) of the P. gingivalis genome was differentially expressed when the bacterium was grown as a biofilm. Genes that were down-regulated in biofilm cells, relative to planktonic cells, included those involved in cell envelope biogenesis, DNA replication, energy production and biosynthesis of cofactors, prosthetic groups and carriers. A number of genes encoding transport and binding proteins were up-regulated in P. gingivalis biofilm cells. Several genes predicted to encode proteins involved in signal transduction and transcriptional regulation were differentially regulated and may be important in the regulation of biofilm growth., Conclusion: This study analyzing global gene expression provides insight into the adaptive response of P. gingivalis to biofilm growth, in particular showing a down regulation of genes involved in growth and metabolic activity.