Electrophoretic resolution of the "major outer membrane protein" of Escherichia coli K12 into four bands

Specificity and mechanism of TonB-dependent ferric catecholate uptake by Fiu

We studied the Escherichia coli outer membrane protein Fiu, a presumed transporter of monomeric ferric catecholates, by introducing Cys residues in its surface loops and modifying them with fluorescein maleimide (FM). Fiu-FM bound iron complexes of the tricatecholate siderophore enterobactin (FeEnt) and glucosylated enterobactin (FeGEnt), their dicatecholate degradation product Fe(DHBS)2 (FeEnt*), the monocatecholates dihydroxybenzoic acid (FeDHBA) and dihydroxybenzoyl serine (FeDHBS), and the siderophore antibiotics cefiderocol (FDC) and MB-1. Unlike high-affinity ligand-gated porins (LGPs), Fiu-FM had only micromolar affinity for iron complexes. Its apparent KD values for FeDHBS, FeDHBA, FeEnt*, FeEnt, FeGEnt, FeFDC, and FeMB-1 were 0.1, 0.7, 0.7, 1.0, 0.3, 0.4, and 4 μM, respectively. Despite its broad binding abilities, the transport repertoires of E. coli Fiu, as well as those of Cir and FepA, were less broad. Fiu only transported FeEnt*. Cir transported FeEnt* and FeDHBS (weakly); FepA transported FeEnt, FeEnt*, and FeDHBA. Both Cir and FepA bound FeGEnt, albeit with lower affinity. Related transporters of Acinetobacter baumannii (PiuA, PirA, BauA) had similarly moderate affinity and broad specificity for di- or monomeric ferric catecholates. Both microbiological and radioisotopic experiments showed Fiu's exclusive transport of FeEnt*, rather than ferric monocatecholate compounds. Molecular docking and molecular dynamics simulations predicted three binding sites for FeEnt*in the external vestibule of Fiu, and a fourth site deeper in its interior. Alanine scanning mutagenesis in the outermost sites (1a, 1b, and 2) decreased FeEnt* binding affinity as much as 20-fold and reduced or eliminated FeEnt* uptake. Finally, the molecular dynamics simulations suggested a pathway of FeEnt* movement through Fiu that may generally describe the process of metal transport by TonB-dependent receptors.

Shigella flexneri Adapts to Niche-Specific Stresses through Modifications in Cell Envelope Composition and Decoration

Shigella flexneri is the primary causative agent of worldwide shigellosis. As the pathogen transverses the distinct niches of the gastrointestinal tract it necessitates dynamic adaptation strategies to mitigate host antimicrobials such as dietary fatty acids (FAs) and the bile salt, deoxycholate (DOC). This study investigates the dynamics of the S. flexneri cell envelope, by interrogating adaptations following FA or DOC exposure. We deciphered the effects of FAs and DOC on bacterial membrane fatty acid and lipopolysaccharide (LPS) compositions. We identified novel LPS-based strategies by the pathogen to support resistance to these host compounds. In particular, expression of S. flexneri very-long O antigen (VL-Oag) LPS was found to play a central role in stress mitigation, as VL-Oag protects against antimicrobial FAs, but its presence rendered S. flexneri susceptible to DOC stress. Collectively, this work underpins the importance for S. flexneri to maintain appropriate regulation of cell envelope constituents, in particular VL-Oag LPS, to adequately adapt to diverse stresses during infection.

Cysteine-Dependent Conformational Heterogeneity of Shigella flexneri Autotransporter IcsA and Implications of Its Function

Shigella IcsA is a versatile surface virulence factor required for early and late pathogenesis stages extracellularly and intracellularly. Despite IcsA serving as a model Type V secretion system (T5SS) autotransporter to study host-pathogen interactions, its detailed molecular architecture is poorly understood. Recently, IcsA was found to switch to a different conformation for its adhesin activity upon sensing the host stimuli by Shigella Type III secretion system (T3SS). Here, we reported that the single cysteine residue (C130) near the N terminus of the IcsA passenger had a role in IcsA adhesin activity. We also showed that the IcsA passenger (IcsAp) existed in multiple conformations, and the conformation populations were influenced by a central pair of cysteine residues (C375 and C379), which was not previously reported for any Type V autotransporter passengers. Disruption of either or both central cysteine residues altered the exposure of IcsA epitopes to polyclonal anti-IcsA antibodies previously shown to block Shigella adherence, yet without loss of IcsA intracellular functions in actin-based motility (ABM). Anti-IcsA antibody reactivity was restored when the IcsA-paired cysteine substitution mutants were expressed in an ΔipaD background with a constitutively active T3SS, highlighting an interplay between T3SS and T5SS. The work here uncovered a novel molecular switch empowered by a centrally localized, short-spaced cysteine pair in the Type V autotransporter IcsA that ensured conformational heterogeneity to aid IcsA evasion of host immunity. IMPORTANCE Shigella species are the leading cause of diarrheal-related death globally by causing bacillary dysentery. The surface virulence factor IcsA, which is essential for Shigella pathogenesis, is a unique multifunctional autotransporter that is responsible for cell adhesion, and actin-based motility, yet detailed mechanistic understanding is lacking. Here, we showed that the three cysteine residues in IcsA contributed to the protein's distinct functions. The N-terminal cysteine residue within the IcsA passenger domain played a role in adhesin function, while a centrally localized cysteine pair provided conformational heterogeneity that resulted in IcsA molecules with different reactivity to adhesion-blocking anti-IcsA antibodies. In synergy with the Type III secretion system, this molecular switch preserved biological function in distinct IcsA conformations for cell adhesion, actin-based motility, and autophagy escape, providing a potential strategy by which Shigella evades host immunity and targets this essential virulence factor.

Subcellular localization of the enterobacterial common antigen GT-E-like glycosyltransferase, WecG

Enterobacterales have developed a specialized outer membrane polysaccharide (enterobacterial common antigen [ECA]). ECA biosynthesis begins on the cytoplasmic side of the inner membrane (IM) where glycosyltransferases sequentially add sugar moieties to form a complete repeat unit which is then translocated across the IM by WzxE before being polymerized into short linear chains by WzyE/WzzE. Research into WecG, the enzyme responsible for generating ECA lipid-II, has not progressed beyond Barr et al. (1988) who described WecG as a membrane protein. Here we revise our understanding of WecG and re-characterize it as a peripherally associated membrane protein. Through the use of Western immunoblotting we show that WecG in Shigella flexneri is maintained to the IM via its three C-terminal helices and further identify key residues in helix II which are critical for this interaction which has allowed us to identify WecG as a GT-E glycosyltransferase. We investigate the possibility of protein complexes and ultimately show that ECA lipid-I maintains WecG to the membrane which is crucial for its function. This research is the first since Barr et al. (1988) to investigate the biochemistry of WecG and reveals possible novel drug targets to inhibit WecG and thus ECA function and cell viability.

Identification of the Shigella flexneri Wzy Domain Modulating WzzpHS-2 Interaction and Detection of the Wzy/Wzz/Oag Complex

Shigella flexneri implements the Wzy-dependent pathway to biosynthesize the O antigen (Oag) component of its surface lipopolysaccharide. The inner membrane polymerase Wzy_SF catalyzes the repeat addition of undecaprenol-diphosphate-linked Oag (Und-PP-RUs) to produce a polysaccharide, the length of which is tightly regulated by two competing copolymerase proteins, Wzz_SF (short-type Oag; 10 to 17 RUs) and Wzz_pHS-2 (very-long-type Oag; >90 RUs). The nature of the interaction between Wzy_SF and Wzz_SF/Wzz_pHS-2 in Oag polymerization remains poorly characterized, with the majority of the literature characterizing the individual protein constituents of the Wzy-dependent pathway. Here, we report instead a major investigation into the specific binding interactions of Wzy_SF with its copolymerase counterparts. For the first time, a region of Wzy_SF that forms a unique binding site for Wzz_pHS-2 has been identified. Specifically, this work has elucidated key Wzy_SF moieties at the N- and C-terminal domains (NTD and CTD) that form an intramolecular pocket modulating the Wzz_pHS-2 interaction. Novel copurification data highlight that disruption of residues within this NTD-CTD pocket impairs the interaction with Wzz_pHS-2 without affecting Wzz_SF binding, thereby specifically disrupting polymerization of longer polysaccharide chains. This study provides a novel understanding of the molecular interaction of Wzy_SF with Wzz_SF/Wzz_pHS-2 in the Wzy-dependent pathway and, furthermore, detects the Wzy/Wzz/Und-PP-Oag complex for the first time. Beyond S. flexneri, this work may be extended to provide insight into the interactions between protein homologues expressed by related species, especially members of Enterobacteriaceae, that produce dual Oag chain length determinants. IMPORTANCE Shigella flexneri is a pathogen causing significant morbidity and mortality, predominantly devastating the pediatric age group in developing countries. A major virulence factor contributing to S. flexneri pathogenesis is its surface lipopolysaccharide, which is comprised of three domains: lipid A, core oligosaccharide, and O antigen (Oag). The Wzy-dependent pathway is the most common biosynthetic mechanism implemented for Oag biosynthesis by Gram-negative bacteria, including S. flexneri. The nature of the interaction between the polymerase, Wzy_SF, and the polysaccharide copolymerases, Wzz_SF and Wzz_pHS-2, in Oag polymerization is poorly characterized. This study investigates the molecular interplay between Wzy_SF and its copolymerases, deciphering key interactions in the Wzy-dependent pathway that may be extended beyond S. flexneri, providing insight into Oag biosynthesis in Gram-negative bacteria.

Expression of membrane beta-barrel protein in E. coli at low temperatures: Structure of Yersinia pseudotuberculosis OmpF porin inclusion bodies

The recombinant OmpF porin of Yersinia pseudotuberculosis as a model of transmembrane protein of the β-barrel structural family was used to study low growth temperature effect on the structure of the produced inclusion bodies (IBs). This porin showed a very low expression level in E. coli at a growth temperature below optimal 37 °C. The introduction of a N-terminal hexahistidine tag into the mature porin molecule significantly increased the biosynthesis of the protein at low cultivation temperatures. The recombinant His-tagged porin (rOmpF-His) was expressed in E. coli at 30 and 18 °C as inclusion bodies (IB-30 and IB-18). The properties and structural organization of IBs, as well as the structure of rOmpF-His solubilized from the IBs with urea and SDS, were studied using turbidimetry, electron microscopy, dynamic light scattering, optical spectroscopy, and amyloid-specific dyes. IB-18, in comparison with IB-30, has a higher solubility in denaturants, suggesting a difference between IBs in the conformation of the associated polypeptide chains. The spectroscopic analysis revealed that rOmpF-His IBs have a high content of secondary structure with a tertiary-structure elements, including a native-like conformation, the proportion of which in IB-18 is higher than in IB-30. Solubilization of the porin from IBs is accompanied by a modification of its secondary structure. The studied IBs also contain amyloid-like structures. The results obtained in this study expand our knowledge of the structural organization of IBs formed by proteins of different structural classes and also have a contribution into the new approaches development of producing functionally active recombinant membrane proteins.

A screening method for binding synthetic metallo-complexes to haem proteins

The introduction of a second coordination sphere, in the form of a protein scaffold, to synthetic catalysts can be beneficial for their reactivity and substrate selectivity. Here we present semi-native polyacrylamide gel electrophoresis (semi-native PAGE) as a rapid screening method for studying metal complex-protein interactions. Such a screening is generally performed using electron spray ionization mass spectrometry (ESI-MS) and/or UV-Vis spectroscopy. Semi-native PAGE analysis has the advantage that it does not rely on spectral changes of the metal complex upon protein interaction and can be applied for high-throughput screening and optimization of complex binding. In semi-native PAGE non-denatured protein samples are loaded on a gel containing sodium dodecyl sulphate (SDS), leading to separation based on differences in structural stability. Semi-native PAGE gel runs of catalyst-protein mixtures were compared to gel runs obtained with native and denaturing PAGE. ESI-MS was additionally realised to confirm protein-complex binding. The general applicability of semi-native PAGE was investigated by screening the binding of various cobalt- and ruthenium-based compounds to three types of haem proteins.

Detection of a disulphide bond and conformational changes in Shigella flexneri Wzy, and the role of cysteine residues in polymerase activity

Shigella flexneri utilises the Wzy-dependent pathway for the production of a plethora of complex polysaccharides, including the lipopolysaccharide O-antigen (Oag) component. The inner membrane protein Wzy_SF polymerises Oag repeat units, whilst two co-polymerase proteins, Wzz_SF and Wzz_pHS-2, together interact with Wzy_SF to regulate production of short- (S-Oag) and very long- (VL-Oag) Oag modal lengths, respectively. The 2D arrangement of Wzy_SF transmembrane and soluble regions has been previously deciphered, however, attaining information on the 3D structural and conformational arrangement of Wzy_SF, or any homologue, has proven difficult. For the first time, the current study detected insights into the in situ Wzy_SF arrangement. In vitro assays using thiol-reactive PEG-maleimide were used to probe Wzy_SF conformation, which additionally detected novel, unique conformational changes in response to interaction with intrinsic factors, including Wzz_SF and Wzz_pHS-2, and extrinsic factors, such as temperature. Site-directed mutagenesis of Wzy_SF cysteine residues revealed the presence of a putative intramolecular disulphide bond, between cysteine moieties 13 and 60. Subsequent analyses highlighted both the structural and functional importance of Wzy_SF cysteines. Substitution of Wzy_SF cysteine residues significantly decreased biosynthesis of the VL-Oag modal length, without disruption to S-Oag production. This phenotype was corroborated in the absence of co-polymerase competition for Wzy_SF interaction. These data suggest Wzy_SF cysteine substitutions directly impair the interaction between Wzy/Wzz_pHS-2, without altering the Wzy/Wzz_SF interplay, and in combination with structural data, we propose that the N- and C-termini of Wzy_SF are arranged in close proximity, and together may form the unique Wzz_pHS-2 interaction site.

Topology of the Shigella flexneri Enterobacterial Common Antigen polymerase WzyE

Enterobacteriales have evolved a specialized outer membrane polysaccharide [Enterobacterial Common Antigen (ECA)] which allows them to persist in various environmental niches. Biosynthesis of ECA initiates on the cytoplasmic leaflet of the inner membrane (IM) where glycosyltransferases assemble ECA repeat units (RUs). Complete RUs are then translocated across the IM and assembled into polymers by ECA-specific homologues of the Wzy-dependent pathway. Consisting of the membrane proteins Wzx, Wzy and Wzz, the Wzy-dependent pathway is the most common polysaccharide biosynthetic pathway in Gram-negative bacteria where it is most notably involved in LPS O antigen (Oag) biosynthesis. As such, the majority of research directed towards these proteins has been orientated towards Oag biosynthetic homologues with little directed towards ECA homologues. Belonging to the Shape, Elongation, Division and Sporulation (SEDS) protein family, Wzy proteins are polymerases, and are characterized as possessing little or no peptide homology among homologues as well as being polytopic membrane proteins with functionally relevant residues within periplasmic loops, as defined by C-terminal reporter fusion topology mapping. Here, we present the first the first major study into the ECA polymerase WzyE. Multiple sequence alignments and topology mapping showed that WzyE is unlike WzyB proteins involved with Oag biosynthesis WzyE displays high peptide conservation across Enterobacteriales. In silico structures and reporter mapping allowed us to identify possible functionally conserved residues with WzyE_SF's periplasmic loops, which we showed were crucial for its function. This work provides novel insight into Wzy proteins and suggests that WzyE is an optimal model to investigate Wzy proteins and the Wzy-dependent pathway.

Fluorescent sensors of siderophores produced by bacterial pathogens

Siderophores are iron-chelating molecules that solubilize Fe³⁺ for microbial utilization and facilitate colonization or infection of eukaryotes by liberating host iron for bacterial uptake. By fluorescently labeling membrane receptors and binding proteins, we created 20 sensors that detect, discriminate, and quantify apo- and ferric siderophores. The sensor proteins originated from TonB-dependent ligand-gated porins (LGPs) of Escherichia coli (Fiu, FepA, Cir, FhuA, IutA, BtuB), Klebsiella pneumoniae (IroN, FepA, FyuA), Acinetobacter baumannii (PiuA, FepA, PirA, BauA), Pseudomonas aeruginosa (FepA, FpvA), and Caulobacter crescentus (HutA) from a periplasmic E. coli binding protein (FepB) and from a human serum binding protein (siderocalin). They detected ferric catecholates (enterobactin, degraded enterobactin, glucosylated enterobactin, dihydroxybenzoate, dihydroxybenzoyl serine, cefidericol, MB-1), ferric hydroxamates (ferrichromes, aerobactin), mixed iron complexes (yersiniabactin, acinetobactin, pyoverdine), and porphyrins (hemin, vitamin B12). The sensors defined the specificities and corresponding affinities of the LGPs and binding proteins and monitored ferric siderophore and porphyrin transport by microbial pathogens. We also quantified, for the first time, broad recognition of diverse ferric complexes by some LGPs, as well as monospecificity for a single metal chelate by others. In addition to their primary ferric siderophore ligands, most LGPs bound the corresponding aposiderophore with ∼100-fold lower affinity. These sensors provide insights into ferric siderophore biosynthesis and uptake pathways in free-living, commensal, and pathogenic Gram-negative bacteria.

Identification of a Region in Shigella flexneri WzyB Disrupting the Interaction with WzzpHS2

Shigella flexneri can synthesize polysaccharide chains having complex sugars and a regulated number of repeating units. S. flexneri lipopolysaccharide O antigen (Oag) is synthesized by the Wzy-dependent pathway, which is the most common pathway used in bacteria for polysaccharide synthesis. The inner membrane protein WzyB polymerizes the Oag repeat units into chains, while the polysaccharide copolymerases WzzB and Wzz_pHS2 determine the average number of repeat units or "the modal length," termed short type and very long type. Our data show for the first time a direct interaction between WzyB and Wzz_pHS2, with and without the use of the chemical cross-linker dithiobis (succinimidyl propionate) (DSP). Additionally, mutations generated via random and site-directed mutagenesis identify a region of WzyB that caused diminished function and significantly decreased very long Oag chain polymerization, and that affected the aforementioned interaction. These results provide insight into the mechanisms underlying the regulation of Oag biosynthesis. IMPORTANCE Complex polysaccharide chains are synthesized by bacteria, usually at a regulated number of repeating units, which has broad implications for bacterial pathogenesis. One example is the O antigen (Oag) component of lipopolysaccharide that is predominantly synthesized by the Wzy-dependent pathway. Our findings show for the first time a direct physical interaction between WzyB and Wzz_pHS2. Additionally, a set of Wzy mutant constructs were generated, revealing a proposed active site/switch region involved in the activity of WzyB and the physical interaction with Wzz_pHS2. Combined, these findings further understanding of the Wzy-dependent pathway. The identification of a novel interaction with the polysaccharide copolymerase Wzz_pHS2 and the region of WzyB that is involved in this aforementioned interaction and its impact on WzyB Oag synthesis activity have significant implication for the prevention/treatment of bacterial diseases and discovery of novel biotechnologies.

Separation of Glycosylated OmpA-Like Proteins from Porphyromonas gingivalis and Tannerella forsythia

OmpA-like proteins located in the outer bacterial membrane are potential virulence factors from the major periodontal pathogens Porphyromonas gingivalis and Tannerella forsythia. Our previous studies have shown that OmpA-like proteins are glycosylated by O-linked N-acetylglucosamine (O-GlcNAc) and are strongly reactive to wheat germ agglutinin (WGA) lectin, which shows sugar specificity to GlcNAc. Utilizing this property, we have developed a separation method for OmpA-like proteins by affinity chromatography using WGA lectin-agarose. The purity of enriched native OmpA-like proteins were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie Brilliant Blue (CBB) staining. More importantly, the purified OmpA-like proteins formed a unique trimeric structure keeping their bioactivity intact. In this chapter, we describe a detailed procedure to separate OmpA-like proteins, which may be used to further progress the biological studies of OmpA-like proteins.

Polysaccharide co-polymerase WzzB/WzzE chimeras reveal transmembrane 2 region of WzzB is important for interaction with WzyB

The ability of bacteria to synthesise complex polysaccharide chains at a controlled number of repeating units has wide implications for a range of biological activities that include: symbiosis, biofilm formation and immune system avoidance. Complex polysaccharide chains such as the O antigen (Oag) component of lipopolysaccharide and the enterobacterial common antigen (ECA) are synthesised by the most common polysaccharide synthesis pathway used in bacteria, known as the Wzy-dependent pathway. The Oag and ECA are polymerized into chains via the inner membrane proteins WzyB and WzyE, respectively, while the respective co-polymerases WzzB and WzzE modulate the number of repeat units in the chains or "the modal length" of the polysaccharide via a hypothesised interaction. Our data shows for the first time "cross-talk" between Oag and ECA synthesis in that WzzE is able to partially regulate Oag modal length via a potential interaction with WzyB. To investigate this, one or both of the transmembrane regions (TM1 and TM2) of WzzE and WzzB were swapped creating six chimera proteins. Several chimeric proteins showed significant increases Oag modal length control, while others reduced control. Additionally, co-purification experiments show an interaction between WzyB and WzzB for the first time without the use of a chemical cross-linker, and a novel interaction between WzyB and WzzE. These results suggest the TM2 region of Wzz proteins plays a critical role in Oag and ECA modal length control, presumably via the interaction with respective Wzy proteins, thus providing insight into the complex mechanism underlying the control of polysaccharide biosynthesis.ImportanceBacteria synthesise complex polysaccharide chains at a controlled number of repeating units, this has wide implications for a range of bacterial activities involved in virulence. Examples of complex polysaccharide chains include, the O antigen (Oag) component of lipopolysaccharide and the enterobacterial common antigen (ECA), both of these examples are predominantly synthesised by their own independent Wzy-dependent pathway. Our data show for the first time "cross-talk" between Oag and ECA synthesis and identifies novel physical protein-protein interactions between proteins in these systems. These findings further the understanding of how the system functions to control polysaccharide chain length which has great implications for novel biotechnologies and/or the combat of bacterial diseases.

Porin from Marine Bacterium Marinomonas primoryensis KMM 3633T: Isolation, Physico-Chemical Properties, and Functional Activity

Marinomonas primoryensis KMM 3633^T, extreme living marine bacterium was isolated from a sample of coastal sea ice in the Amursky Bay near Vladivostok, Russia. The goal of our investigation is to study outer membrane channels determining cell permeability. Porin from M. primoryensis KMM 3633^T (MpOmp) has been isolated and characterized. Amino acid analysis and whole genome sequencing were the sources of amino acid data of porin, identified as Porin_4 according to the conservative domain searching. The amino acid composition of MpOmp distinguished by high content of acidic amino acids and low content of sulfur-containing amino acids, but there are no tryptophan residues in its molecule. The native MpOmp existed as a trimer. The reconstitution of MpOmp into black lipid membranes demonstrated its ability to form ion channels whose conductivity depends on the electrolyte concentration. The spatial structure of MpOmp had features typical for the classical gram-negative porins. However, the oligomeric structure of isolated MpOmp was distinguished by very low stability: heat-modified monomer was already observed at 30 °C. The data obtained suggest the stabilizing role of lipids in the natural membrane of marine bacteria in the formation of the oligomeric structure of porin.

Conformational rearrangements in the N-domain of Escherichia coli FepA during ferric enterobactin transport

The Escherichia coli outer membrane receptor FepA transports ferric enterobactin (FeEnt) by an energy- and TonB-dependent, but otherwise a mechanistically undetermined process involving its internal 150-residue N-terminal globular domain (N-domain). We genetically introduced pairs of Cys residues in different regions of the FepA tertiary structure, with the potential to form disulfide bonds. These included Cys pairs on adjacent β-strands of the N-domain (intra-N) and Cys pairs that bridged the external surface of the N-domain to the interior of the C-terminal transmembrane β-barrel (inter-N-C). We characterized FeEnt uptake by these mutants with siderophore nutrition tests, [⁵⁹Fe]Ent binding and uptake experiments, and fluorescence decoy sensor assays. The three methods consistently showed that the intra-N disulfide bonds, which restrict conformational motion within the N-domain, prevented FeEnt uptake, whereas most inter-N-C disulfide bonds did not prevent FeEnt uptake. These outcomes indicate that conformational rearrangements must occur in the N terminus of FepA during FeEnt transport. They also argue against disengagement of the N-domain out of the channel as a rigid body and suggest instead that it remains within the transmembrane pore as FeEnt enters the periplasm.

The virulence domain of Shigella IcsA contains a subregion with specific host cell adhesion function

Shigella species cause bacillary dysentery, especially among young individuals. Shigellae target the human colon for invasion; however, the initial adhesion mechanism is poorly understood. The Shigella surface protein IcsA, in addition to its role in actin-based motility, acts as a host cell adhesin through unknown mechanism(s). Here we confirmed the role of IcsA in cell adhesion and defined the region required for IcsA adhesin activity. Purified IcsA passenger domain was able block S. flexneri adherence and was also used as a molecular probe that recognised multiple components from host cells. The region within IcsA's functional passenger domain (aa 138-148) was identified by mutagenesis. Upon the deletion of this region, the purified IcsAΔ138-148 was found to no longer block S. flexneri adherence and had reduced ability to interact with host molecules. Furthermore, S. flexneri expressing IcsAΔ138-148 was found to be significantly defective in both cell adherence and invasion. Taken together, our data identify an adherence region within the IcsA functional domain and provides useful information for designing therapeutics for Shigella infection.

Inclusion Bodies of Recombinant OmpF Porin from Yersinia pseudotuberculosis: Properties and Structural Characterization

Mature pore-forming OmpF protein from the outer membrane of Yersinia pseudotuberculosis was expressed in Escherichia coli in the form of inclusion bodies (IBs) under different cultivation conditions. The properties and structural organization of the IBs as well as the structure of the recombinant porin (rOmpF) solubilized from the IBs were investigated using electron microscopy, dynamic light scattering, optical spectroscopy, and specific hydrophobic dyes. The size, shape, and stability of the IBs under denaturing solutions were determined. It was found that the IBs were readily soluble in SDS and more resistant to urea. Dissolution of the IBs in both denaturing agents led to formation of a heterogeneous in size population of oligomeric particles. The IBs contained an intermediate form of the rOmpF with native-like secondary structure and elements of tertiary structure, which was able to penetrate a lipid bilayer and adopt a functionally active conformation. There were no significant differences in the properties and structure between the examined IBs formed at different concentrations of the inducer (IPTG). However, the content of amyloids in the IBs increased with increasing concentration of the inducer. These results contribute to the development of new approaches for the production of active proteins from IBs, as well as biologically and functionally active IBs.

The role of polyproline motifs in the histidine kinase EnvZ

Although distinct amino acid motifs containing consecutive prolines (polyP) cause ribosome stalling, which necessitates recruitment of the translation elongation factor P (EF-P), they occur strikingly often in bacterial proteomes. For example, polyP motifs are found in more than half of all histidine kinases in Escherichia coli K-12, which raises the question of their role(s) in receptor function. Here we have investigated the roles of two polyP motifs in the osmosensor and histidine kinase EnvZ. We show that the IPPPL motif in the HAMP domain is required for dimerization of EnvZ. Moreover, replacement of the prolines in this motif by alanines disables the receptor’s sensor function. The second motif, VVPPA, which is located in the periplasmic domain, was found to be required for interaction with the modulator protein MzrA. Our study also reveals that polyP-dependent stalling has little effect on EnvZ levels. Hence, both polyP motifs in EnvZ are primarily involved in protein-protein interaction. Furthermore, while the first motif occurs in almost all EnvZ homologues, the second motif is only found in species that have MzrA, indicating co-evolution of the two proteins.

Energy dispersive spectroscopy-scanning transmission electron microscope observations of free radical production in human polymorphonuclear leukocytes phagocytosing non-opsonized Tannerella forsythia

We investigated the association between human polymorphonuclear leukocytes (PMNs) and non-opsonized Tannerella forsythia ATCC 43037 displaying a serum-resistant surface layer (S-layer). When PMNs were mixed with T. forsythia in suspension, the cells phagocytosed T. forsythia cells. Nitro blue tetrazolium (NBT) reduction, indicative of O2- production, was observed by light microscopy; cerium (Ce) perhydroxide deposition, indicative of H₂ O₂ production, was observed by electron microscopy. We examined the relationship between high-molecular-weight proteins of the S-layer and Ce reaction (for T. forsythia phagocytosis) using electron microscopic immunolabeling. Immunogold particles were localized within the PMNs and on cell surfaces, labelling at the same Ce-reacted sites where the S-layer was present. We then used energy dispersive spectroscopy (EDS)-scanning transmission electron microscope (STEM) to perform Ce and nitrogen (N) (for S-layer immunocytochemistry) elemental analysis on the phagocytosed cells. That is, the elemental mapping and analysis of N by EDS appeared to reflect the presence of the same moieties detected by the 3,3'-diaminobenzidine-tetrahydrochloride (DAB) reaction with horseradish peroxidase (HRP)-conjugated secondary antibodies, instead of immunogold labeling. We focused on the use of EDS-STEM to visualize the presence of N resulting from the DAB reaction. In a parallel set of experiments, we used EDS-STEM to perform Ce and gold (Au; from immunogold labeling of the S-layer) elemental analysis on the same phagocytosing cells.

Peculiarities of thermal denaturation of OmpF porin from Yersinia ruckeri

Irreversible denaturation of membrane proteins in detergent solutions is similar to unfolding of water-soluble multidomain proteins and represents a complex, multistage process.

Resistance of Serratia marcescens to polymyxin B: a comparative investigation of two S-form lipopolysaccharides obtained from a sensitive and a resistant variant of strain 111

Lipopolysaccharide (LPS) of the polymyxin B (PmB)-sensitive variant of Serratia marcescens smooth-type strain 111 (senLPS) binds significantly more PmB than that of the resistant variant (resLPS), following mild acid hydrolysis this difference is abolished. The main compositional differences between these strains are: (i) the amount of 4-amino-4-deoxy-arabinose (Ara4N); and (ii) the substitution patterns of the phosphate groups. ResLPS contains three times more Ara4N than senLPS, mainly phosphodiesters, whereas senLPS contains mainly (di)-phosphomonoesters. Thus, the senLPS, and the bacterial surface, contain a higher negative charge density. Mild acid hydrolysis decreases the PmB-binding capacity of senLPS and increases that of resLPS. The resulting change in LPS composition was a reduction in the amount of phosphate (about 40%) and a loss of nearly all the Ara4N residues, from both LPS. Mild alkaline hydrolysis removes Ara4N from both LPS, and the hydrolysate contains Ara4N-phosphate, but no Ara4N-(1 →8)-Kdo was detected. The results suggest that the 4'-phosphate of lipid A mediates the binding of PmB, whereas its substitution by Ara4N prevents it.

Conserved transmembrane glycine residues in the Shigella flexneri polysaccharide co-polymerase protein WzzB influence protein-protein interactions

The O antigen (Oag) component of lipopolysaccharides (LPS) is crucial for virulence and Oag chain-length regulation is controlled by the polysaccharide co-polymerase class 1 (PCP1) proteins. Crystal structure analyses indicate that structural conservation among PCP1 proteins is highly maintained, however the mechanism of Oag modal-chain-length control remains to be fully elucidated. Shigella flexneri PCP1 protein WzzBSF confers a modal-chain length of 10-17 Oag repeat units (RUs), whereas the Salmonella enterica Typhimurium PCP1 protein WzzBST confers a modal-chain length of ~16-28 Oag RUs. Both proteins share >70 % overall sequence identity and contain two transmembrane (TM1 and TM2) regions, whereby a conserved proline-glycine-rich motif overlapping the TM2 region is identical in both proteins. Conserved glycine residues within TM2 are functionally important, as glycine to alanine substitutions at positions 305 and 311 confer very short Oag modal-chain length (~2-6 Oag RUs). In this study, WzzBSF was co-expressed with WzzBST in S. flexneri and a single intermediate modal-chain length of ~11-21 Oag RUs was observed, suggesting the presence of Wzz:Wzz interactions. Interestingly, co-expression of WzzBSF with WzzBG305A/G311A conferred a bimodal LPS Oag chain length (despite over 99 % protein sequence identity), and we hypothesized that the proteins fail to interact. Co-purification assays detected His6-WzzBSF co-purifying with FLAG-tagged WzzBST but not with FLAG-tagged WzzBG305A/G311A, supporting our hypothesis. These data indicate that the conserved glycine residues in TM2 are involved in Wzz:Wzz interactions, and provide insight into key interactions that drive Oag modal length control.

Single channel activity of OmpF-like porin from Yersinia pseudotuberculosis

To gain a mechanistic insight in the functioning of the OmpF-like porin from Yersinia pseudotuberculosis (YOmpF), we compared the effect of pH variation on the ion channel activity of the protein in planar lipid bilayers and its binding to lipid membranes. The behavior of YOmpF channels upon acidification was similar to that previously described for Escherichia coli OmpF. In particular, a decrease in pH of the bathing solution resulted in a substantial reduction of YOmpF single channel conductance, accompanied by the emergence of subconductance states. Similar subconductance substates were elicited by the addition of lysophosphatidylcholine. This observation, made with porin channels for the first time, pointed to the relevance of lipid-protein interactions, in particular, the lipid curvature stress, to the appearance of subconductance states at acidic pH. Binding of YOmpF to membranes displayed rather modest dependence on pH, whereas the channel-forming potency of the protein tremendously decreased upon acidification.

Structural and Biochemical Analysis of a Single Amino-Acid Mutant of WzzBSF That Alters Lipopolysaccharide O-Antigen Chain Length in Shigella flexneri

Lipopolysaccharide (LPS), a surface polymer of Gram-negative bacteria, helps bacteria survive in different environments and acts as a virulence determinant of host infection. The O-antigen (Oag) component of LPS exhibits a modal chain-length distribution that is controlled by polysaccharide co-polymerases (PCPs). The molecular basis of the regulation of Oag chain-lengths remains unclear, despite extensive mutagenesis and structural studies of PCPs from Escherichia coli and Shigella. Here, we identified a single mutation (A107P) of the Shigella flexneri WzzBSF, by a random mutagenesis approach, that causes a shortened Oag chain-length distribution in bacteria. We determined the crystal structures of the periplasmic domains of wild-type WzzBSF and the A107P mutant. Both structures form a highly similar open trimeric assembly in the crystals, and show a similar tendency to self-associate in solution. Binding studies by bio-layer interferometry reveal cooperative binding of very short (VS)-core-plus-O-antigen polysaccharide (COPS) to the periplasmic domains of both proteins, but with decreased affinity for the A107P mutant. Our studies reveal that subtle and localized structural differences in PCPs can have dramatic effects on LPS chain-length distribution in bacteria, for example by altering the affinity for the substrate, which supports the role of the structure of the growing Oag polymer in this process.

A small conserved motif supports polarity augmentation of Shigella flexneri IcsA

The rod-shaped enteric intracellular pathogen Shigella flexneri and other Shigella species are the causative agents of bacillary dysentery. S. flexneri are able to spread within the epithelial lining of the gut, resulting in lesion formation, cramps and bloody stools. The outer membrane protein IcsA is essential for this spreading process. IcsA is the initiator of an actin-based form of motility whereby it allows the formation of a filamentous actin 'tail' at the bacterial pole. Importantly, IcsA is specifically positioned at the bacterial pole such that this process occurs asymmetrically. The mechanism of IcsA polarity is not completely understood, but it appears to be a multifactorial process involving factors intrinsic to IcsA and other regulating factors. In this study, we further investigated IcsA polarization by its intramolecular N-terminal and central polar-targeting (PT) regions (nPT and cPT regions, respectively). The results obtained support a role in polar localization for the cPT region and contend the role of the nPT region. We identified single IcsA residues that have measurable impacts on IcsA polarity augmentation, resulting in decreased S. flexneri sprading efficiency. Intriguingly, regions and residues involved in PT clustered around a highly conserved motif which may provide a functional scaffold for polarity-augmenting residues. How these results fit with the current model of IcsA polarity determination is discussed.

Detection of Wzy/Wzz interaction in Shigella flexneri

The O antigen (Oag) component of Shigella flexneri lipopolysaccharide (LPS) is important for virulence and a protective antigen. It is synthesized by the Wzy-dependent mechanism. S. flexneri Wzy has 12 transmembrane segments and two large periplasmic loops. The modal chain length of the Oag is determined by Wzz. Experimental evidence supports multi-protein interactions in the Wzy-dependent pathway. However, evidence for direct interaction of Wzy with the other proteins of the Wzy-dependent pathway is limited. Initially, we purified Wzy-GFP-His8 and detected the presence of a dimeric form. In vivo cross-linking was then performed in an S. flexneri wzy mutant strain carrying plasmids encoding Wzy-GFP-His8 and untagged Wzz. Following solubilization with n-dodecyl-β-D-maltopyranoside (DDM) and affinity purification of Wzy-GFP-His8, Western immunoblotting with Wzz antibody detected co-purification of Wzz; this was supported by MS analysis. To the best of our knowledge, this is the first reported isolation of a complex between Wzy and Wzz. Wzy mutants (WzyR164A, WzyV92M, WzyY137H, and WzyR250K) whose properties are affected by Wzz were able to form complexes with Wzz. Their mutational alterations did not affect the interaction of Wzy with Wzz. Thus, the interaction may involve many regions of Wzy.

The passenger-associated transport repeat promotes virulence factor secretion efficiency and delineates a distinct autotransporter subtype

Autotransporters are a superfamily of virulence factors secreted by Gram negative bacteria. They are comprised of an N-terminal passenger domain that is translocated across the outer membrane and a C-terminal domain that inserts into the outer membrane forming a β-barrel anchor. It is still poorly understood how the passenger is efficiently translocated in the absence of external energy inputs. Several mechanisms have been proposed in solution of this problem, yet due to the vast diversity of size, sequence and function of the passenger, it is not clear how widely these mechanisms are employed. In this study we functionally characterize a conserved repeat found in many passengers that we designate the Passenger-associated Transport Repeat (PATR). Using the autotransporter IcsA from the enteropathogen Shigella flexneri, we identified conserved PATR residues that are required for efficient export of the passenger during growth and infection. Furthermore, PATR-containing autotransporters are significantly larger than non-PATR autotransporters, with PATR copy number correlating with passenger size. We also show that PATR-containing autotransporters delineate a subgroup that associates with specific virulence traits and architectures. These results advance our understanding of autotransporter composition and indicate that an additional transport mechanism is important for thousands of these proteins.

A new biofilm-associated colicin with increased efficiency against biofilm bacteria

Formation of bacterial biofilm communities leads to profound physiological modifications and increased physical and metabolic exchanges between bacteria. It was previously shown that bioactive molecules produced within the biofilm environment contribute to bacterial interactions. Here we describe new pore-forming colicin R, specifically produced in biofilms formed by the natural isolate Escherichia coli ROAR029 but that cannot be detected under planktonic culture conditions. We demonstrate that an increased SOS stress response within mature biofilms induces SOS-dependent colicin R expression. We provide evidence that colicin R displays increased activity against E. coli strains that have a reduced lipopolysaccharide length, such as the pathogenic enteroaggregative E. coli LF82 clinical isolate, therefore pointing to lipopolysaccharide size as an important determinant for resistance to colicins. We show that colicin R toxicity toward E. coli LF82 is increased under biofilm conditions compared with planktonic susceptibility and that release of colicin R confers a strong competitive advantage in mixed biofilms by rapidly outcompeting sensitive neighboring bacteria. This work identifies the first biofilm-associated colicin that preferentially targets biofilm bacteria. Furthermore, it indicates that the study of antagonistic molecules produced in biofilm and multispecies contexts could reveal unsuspected, ecologically relevant bacterial interactions influencing population dynamics in natural environments.

Relationship between O-antigen chain length and resistance to colicin E2 in Shigella flexneri

The Shigella flexneri polysaccharide co-polymerase class 1a (PCP1a) protein, WzzBSF, regulates LPS O-antigen (Oag) chain length to confer short (S)-type Oag chains of ~10-17 Oag repeat units (RUs). The S-type Oag chains affect Shigella flexneri virulence as they influence IcsA-mediated actin-based motility. However, they do not confer resistance to complement; this is conferred by the very-long (VL)-type Oag chains determined by WzzB(pHS2). Colicins are bacterial proteins produced by some Escherichia coli strains to kill related strains. While the presence of Oag chains has been shown to shield outer-membrane proteins from colicins, the impact of Oag chain length against colicins is unknown. In this study, initial testing indicated that a Shigella flexneri Y wzz : : kan(r) mutant was more sensitive to colicin E2 compared with the WT strain. Plasmids encoding Wzz mutant and WT PCP1a proteins conferring different Oag modal chain lengths were then expressed in the mutant background, and tested against purified colicin E2. Analysis of swab and spot sensitivity assays showed that strains expressing either S-type or long (L)-type Oag chains (16-28 Oag RUs) conferred greater resistance to colicin E2 compared with strains having very-short-type (2-8 Oag RUs), intermediate-short-type (8-14 Oag RUs) or VL-type (>80 Oag RUs) Oag chains. These results suggest a novel role for LPS Oag chain length control that may have evolved due to selection pressure from colicins in the environment.

Analysis of Major Virulence Factors inPorphyromonas gingivalisunder Various Culture Temperatures Using Specific Antibodies

Porphyromonas gingivalis is implicated in the occurrence of adult periodontitis. We have previously identified major outer membrane proteins from P. gingivalis, which include representative virulence factors such as gingipains, a 75 kDa major protein, RagA, RagB, and putative porin. Fimbriae, another important virulence factor, exist on the cell surface. In this study, we identified major supernatant proteins. They were fimbrilin, the 75 kDa major protein, gingipains and their adhesin domains. Microscopic examination showed that supernatant proteins formed vesicle-like and fimbrial structures. To learn more about the character of this bacterium, we examined effects of growth temperature on localization and expression of these virulence factors. In general, localization of major virulence factors did not change at the various growth temperatures used. Most of the 75 kDa major protein, RagA, RagB, and putative porin were found in the envelope fraction, not in cell-free culture supernatant. Gingipains were found in both the envelope fraction and supernatant. More than 80% of fimbriae were associated with cells, less than 20% migrated to the supernatant. Most fimbriae existed in the whole cell lysate, although there was a small amount in the envelope fraction. When the growth temperature was increased, expression of fimbriae, gingipains, the 75 kDa major protein, RagA, and RagB decreased. However, temperature had almost no effect on expression of putative porin. The tendency for expression of major virulence factors to decrease at higher temperatures may enable P. gingivalis to survive under hostile conditions.

LPS unmasking of Shigella flexneri reveals preferential localisation of tagged outer membrane protease IcsP to septa and new poles

The Shigella flexneri outer membrane (OM) protease IcsP (SopA) is a member of the enterobacterial Omptin family of proteases which cleaves the polarly localised OM protein IcsA that is essential for Shigella virulence. Unlike IcsA however, the specific localisation of IcsP on the cell surface is unknown. To determine the distribution of IcsP, a haemagglutinin (HA) epitope was inserted into the non-essential IcsP OM loop 5 using Splicing by Overlap Extension (SOE) PCR, and IcsP(HA) was characterised. Quantum Dot (QD) immunofluorescence (IF) surface labelling of IcsP(HA) was then undertaken. Quantitative fluorescence analysis of S. flexneri 2a 2457T treated with and without tunicaymcin to deplete lipopolysaccharide (LPS) O antigen (Oag) showed that IcsP(HA) was asymmetrically distributed on the surface of septating and non-septating cells, and that this distribution was masked by LPS Oag in untreated cells. Double QD IF labelling of IcsP(HA) and IcsA showed that IcsP(HA) preferentially localised to the new pole of non-septating cells and to the septum of septating cells. The localisation of IcsP(HA) in a rough LPS S. flexneri 2457T strain (with no Oag) was also investigated and a similar distribution of IcsP(HA) was observed. Complementation of the rough LPS strain with rmlD resulted in restored LPS Oag chain expression and loss of IcsP(HA) detection, providing further support for LPS Oag masking of surface proteins. Our data presents for the first time the distribution for the Omptin OM protease IcsP, relative to IcsA, and the effect of LPS Oag masking on its detection.

Antibiotic trapping by plasmid-encoded CMY-2 β-lactamase combined with reduced outer membrane permeability as a mechanism of carbapenem resistance in Escherichia coli

A liver transplant patient was admitted with cholangitis, for which meropenem therapy was started. Initial cultures showed a carbapenem-susceptible (CS) Escherichia coli strain, but during admission, a carbapenem-resistant (CR) E. coli strain was isolated. Analysis of the outer membrane protein profiles showed that both CS and CR E. coli lacked the porins OmpF and OmpC. Furthermore, PCR and sequence analysis revealed that both CS and CR E. coli possessed bla(CTX-M-15) and bla(OXA-1). The CR E. coli strain additionally harbored bla(CMY-2) and demonstrated a >15-fold increase in β-lactamase activity against nitrocefin, but no hydrolysis of meropenem was detected. However, nitrocefin hydrolysis appeared strongly inhibited by meropenem. Furthermore, the CMY-2 enzyme demonstrated lower electrophoretic mobility after its incubation either in vitro or in vivo with meropenem, indicative of its covalent modification with meropenem. The presence of the acyl-enzyme complex was confirmed by mass spectrometry. By transformation of the CMY-2-encoding plasmid into various E. coli strains, it was established that both porin deficiency and high-level expression of the enzyme were needed to confer meropenem resistance. In conclusion, carbapenem resistance emerged by a combination of elevated β-lactamase production and lack of porin expression. Due to the reduced outer membrane permeability, only small amounts of meropenem can enter the periplasm, where they are trapped but not degraded by the large amount of the β-lactamase. This study, therefore, provides evidence that the mechanism of "trapping" by CMY-2 β-lactamase plays a role in carbapenem resistance.

Improved production process for native outer membrane vesicle vaccine against Neisseria meningitidis

An improved detergent-free process has been developed to produce vaccine based on native outer membrane vesicles (NOMV) against Neisseria meningitidis serogroup B. Performance was evaluated with the NonaMen vaccine concept, which provides broad coverage based on nine distinct PorA antigens. Scalable aseptic equipment was implemented, replacing undesirable steps like ultracentrifugation, inactivation with phenol, and the use of preservatives. The resulting process is more consistent and gives a higher yield than published reference processes, enabling NOMV production at commercial scale. Product quality met preliminary specifications for 9 consecutive batches, and an ongoing study confirmed real-time stability up to 12 months after production. As the NOMV had low endotoxic activity and induced high bactericidal titres in mice, they are expected to be safe and effective in humans. The production process is not limited to NonaMen and may be applicable for other N. meningitidis serogroups and other gram-negative pathogens. The current results therefore facilitate the late-stage development and clinical evaluation of NOMV vaccines.

Residues located inside the Escherichia coli FepE protein oligomer are essential for lipopolysaccharide O-antigen modal chain length regulation

The Escherichia coli O157 : H7 FepE protein regulates lipopolysaccharide (LPS) O-antigen (Oag) chain length to confer a very long modal chain length of >80 Oag repeat units (RUs). The mechanism by which FepE regulates Oag modal chain length and the regions within it that are important for its function remain unclear. Studies on the structure of FepE show that the protein oligomerizes. However, the exact size of the oligomer is in dispute, further hampering our understanding of its mechanism. Guided by information previously obtained for regions known to be important for Oag modal chain length determination in the homologous Shigella flexneri WzzBSF protein, a set of FepE mutant constructs with single amino acid substitutions was created. Analysis of the resulting LPS conferred by these mutant His6-FepE proteins showed that amino acid substitutions of leucine 168 (L168) and aspartic acid 268 (D268) resulted in LPS with consistently shortened Oag chain lengths of <80 Oag RUs. Substitution of FepE's transmembrane cysteine residues did not affect function. Chemical cross-linking experiments on mutant FepE proteins showed no consistent correlation between oligomer size and functional activity, and MS analysis of FepE oligomers indicated that the in vivo size of FepE is consistent with a maximum size of a hexamer. Our findings suggest that different FepE residues, mainly located within the internal cavity of the oligomer, contribute to Oag modal chain length determination but not the oligomeric state of the protein.

Identification of Shigella flexneri IcsA residues affecting interaction with N-WASP, and evidence for IcsA-IcsA co-operative interaction

The Shigella flexneri IcsA (VirG) protein is a polarly distributed outer membrane protein that is a fundamental virulence factor which interacts with neural Wiskott-Aldrich syndrome protein (N-WASP). The activated N-WASP then activates the Arp2/3 complex which initiates de novo actin nucleation and polymerisation to form F-actin comet tails and allows bacterial cell-to-cell spreading. In a previous study, IcsA was found to have three N-WASP interacting regions (IRs): IR I (aa 185-312), IR II (aa 330-382) and IR III (aa 508-730). The aim of this study was to more clearly define N-WASP interacting regions II and III by site-directed mutagenesis of specific amino acids. Mutant IcsA proteins were expressed in both smooth lipopolysaccharide (S-LPS) and rough LPS (R-LPS) S. flexneri strains and characterised for IcsA production level, N-WASP recruitment and F-actin comet tail formation. We have successfully identified new amino acids involved in N-WASP recruitment within different N-WASP interacting regions, and report for the first time using co-expression of mutant IcsA proteins, that N-WASP activation involves interactions with different regions on different IcsA molecules as shown by Arp3 recruitment. In addition, our findings suggest that autochaperone (AC) mutant protein production was not rescued by another AC region provided in trans, differing to that reported for two other autotransporters, PrtS and BrkA autotransporters.

Energy filtering transmission electron microscopy immunocytochemistry and antigen retrieval of surface layer proteins from Tannerella forsythensis using microwave or autoclave heating with citraconic anhydride

Tannerella forsythensis (Bacteroides forsythus), an anaerobic Gram-negative species of bacteria that plays a role in the progression of periodontal disease, has a unique bacterial protein profile. It is characterized by two unique protein bands with molecular weights of more than 200 kDa. It also is known to have a typical surface layer (S-layer) consisting of regularly arrayed subunits outside the outer membrane. We examined the relationship between high molecular weight proteins and the S-layer using electron microscopic immunolabeling with chemical fixation and an antigen retrieval procedure consisting of heating in a microwave oven or autoclave with citraconic anhydride. Immunogold particles were localized clearly at the outermost cell surface. We also used energy-filtering transmission electron microscopy (EFTEM) to visualize 3, 3'-diaminobenzidine tetrahydrochloride (DAB) reaction products after microwave antigen retrieval with 1% citraconic anhydride. The three-window method for electron spectroscopic images (ESI) of nitrogen by the EFTEM reflected the presence of moieties demonstrated by the DAB reaction with horseradish peroxidase (HRP)-conjugated secondary antibodies instead of immunogold particles. The mapping patterns of net nitrogen were restricted to the outermost cell surface.

Absence of O antigen suppresses Shigella flexneri IcsA autochaperone region mutations

The Shigella flexneri IcsA (VirG) protein is a polarly distributed autotransporter protein. IcsA functions as a virulence factor by interacting with the host actin regulatory protein N-WASP, which in turn activates the Arp2/3 complex, initiating actin polymerization. Formation of F-actin comet tails allows bacterial cell-to-cell spreading. Although various accessory proteins such as periplasmic chaperones and the β-barrel assembly machine (BAM) complex have been shown to be involved in the export of IcsA, the IcsA translocation mechanism remains to be fully elucidated. A putative autochaperone (AC) region (amino acids 634-735) located at the C-terminal end of the IcsA passenger domain, which forms part of the self-associating autotransporter (SAAT) domain, has been suggested to be required for IcsA biogenesis, as well as for N-WASP recruitment, based on mutagenesis studies. IcsA(i) proteins with linker insertion mutations within the AC region have a significant reduction in production and are defective in N-WASP recruitment when expressed in smooth LPS (S-LPS) S. flexneri. In this study, we have found that the LPS O antigen plays a role in IcsA(i) production based on the use of an rmlD (rfbD) mutant having rough LPS (R-LPS) and a novel assay in which O antigen is depleted using tunicamycin treatment and then regenerated. In addition, we have identified a new N-WASP binding/interaction site within the IcsA AC region.

Self-association of the Shigella flexneri IcsA autotransporter protein

The IcsA autotransporter protein is a major virulence factor of the human intracellular pathogen Shigella flexneri. IcsA is distributed at the poles in the outer membrane (OM) of S. flexneri and interacts with components of the host actin-polymerization machinery to facilitate intracellular actin-based motility and subsequent cell-to-cell spreading of the bacterium. We sought to characterize the biochemical properties of IcsA in the bacterial OM. Chemical cross-linking data suggested that IcsA exists in a complex in the OM. Furthermore, reciprocal co-immunoprecipitation of differentially epitope-tagged IcsA proteins indicated that IcsA is able to self-associate. The identification of IcsA linker-insertion mutants that were negatively dominant provided genetic evidence of IcsA-IcsA interactions. From these results, we propose a model whereby IcsA self-association facilitates efficient actin-based motility.

The role of WlaRG, WlaTB and WlaTC in lipooligosaccharide synthesis by Campylobacter jejuni strain 81116

Campylobacter jejuni is a major bacterial cause of gastroenteritis world-wide. C. jejuni produces a range of glycans including lipooligosaccharide (LOS), an important virulence factor. The genetic content of the LOS synthesis locus varies between C. jejuni strains and 19 classes have been described. Three LOS synthesis genes of C. jejuni strain 81116 (NCTC 11828), wlaRG, wlaTB and wlaTC were the focus of this study. WlaRG and the remaining two proteins of interest share sequence similarity to aminotransferases and glycosyltransferases, respectively. These genes were insertionally inactivated and phenotypically characterised. Each mutant produced truncated LOS. Mutants lacking WlaRG, WlaTB and WlaTC produced LOS with reduced immunogenicity. Both the wlaRG and wlaTC mutants were non-motile and aflagellate. In vitro invasion and adhesion assays revealed that the wlaRG, wlaTB and wlaTC mutants displayed reduced adherence to chicken embryo fibroblasts. All mutants were less invasive of human cells than 81116 confirming the role of intact LOS during invasion of human cells in vitro. Here we propose the general composition for the 81116 LOS core backbone based on capillary electrophoresis-mass spectrometry.

The effectiveness of Echinacea extract or composite glucosamine, chondroitin and methyl sulfonyl methane supplements on acute and chronic rheumatoid arthritis rat model

The study aimed to investigate the effect of the oral administration for 15 days of either Echinacea (E) or genuphil (a composite of chondroitin sulphate, glucosamine and methyl sulfonyl methane [GCM]) nutraceutical supplements on female rat model of acute or chronic arthritis induced by bacterial outer membrane protein (OMP) from faecal flora of healthy and rheumatic humans. Anti-cyclic citrullinated peptide (anti-CCP2), C-reactive protein (CRP) and rheumatoid factor (RF) values increased ( p < 0.05) in both arthritic groups as compared to normal values. The rheumatic markers anti-CCP2, CRP and RF values decreased significantly in E- and GCM-treated groups compared to arthritic none-treated acute or chronic groups. The results of RF values of GCM-treated groups in acute and chronic models decreased exhibiting no statistical difference compared with the normal value. Histological examinations of the hind paw sections revealed moderate inflammation, oedema and mild proliferation of synovial cells in acute arthritic rats and more damage to cartilage and bone with severe inflammation in chronic ones. Echinacea acute treated group showed edema with proliferated synovial membrane and partial damage in cartilage and bone. While in the E -chronic treated group, rough edge with destructed cartilage and bone existed. However, the acute GCM group revealed mild cartilage damage. But the chronic GCM group showed mild synovial cells proliferation and revealed no inflammation with mild cartilage damage edge. Results demonstrated the OMP arthropathic property and through promising light on arthritis treatment using E- or GCM, with the advantage of GMC results over that of E -. The composite GCM is needed for further studies over the dose and duration to assess its preventive effects against the bacterial OMP arthrogenicity.

OmpA-like protein influences cell shape and adhesive activity of Tannerella forsythia

Tannerella forsythia, a gram-negative fusiform rod, is implicated in several types of oral anaerobic infections. Most gram-negative bacteria have OmpA-like proteins that are homologous to the OmpA protein in Escherichia coli. We identified an OmpA-like protein in T. forsythia encoded by the tf1331 gene as one of the major proteins by mass spectrometric analysis. Two-dimensional, diagonal electrophoresis showed that the OmpA-like protein formed a dimeric or trimeric structure via intermolecular disulfide bonds. A biotin labeling experiment revealed that a portion of the protein was exposed on the cell surface, even though T. forsythia possesses an S-layer at the outermost cell surface. Using a tf1331-deletion mutant, we showed that the OmpA-like protein affected cell morphology. The length of the mutant cell was reduced almost by half. Cell swelling was observed in more than 40% of the mutant cells. Moreover, the mutant exhibited decreased adhesion to fibronectin, retarded autoaggregation, and reduced cell surface hydrophobicity. These results suggest that the OmpA-like protein in T. forsythia plays an important role in cellular integrity and adhesive function.

Bacteriophage Lambda as a Delivery Vector for Tn10-Derived Transposons in Xenorhabdus bovienii

Xenorhabdus bovienii wild-type strains lack a functional receptor protein (LamB) in the outer membrane and as a result are unable to adsorb coliphage lambda (lambda). Introduction of plasmids encoding lamB into X. bovienii T228 results in constitutive expression of LamB in the outer membrane of this organism. LamB-expressing strains of X. bovienii adsorb lambda bacteriophage particles and can be used as hosts for lambda::Tn constructs. A Tn10-derived transposon, element 9 (J. C. Way, D. Davis, D. Morisato, D. E. Roberts, and N. Kleckner, Gene 32:369-379, 1984) was used to construct a variety of insertion mutants of X. bovienii. Mutants that had altered expression of protease, lipase, DNase, dye-binding capability, and hemolytic activity, in addition to a series of auxotrophic mutants, were isolated.

Mutagenesis and chemical cross-linking suggest that Wzz dimer stability and oligomerization affect lipopolysaccharide O-antigen modal chain length control

In Shigella flexneri, the polysaccharide copolymerase (PCP) protein Wzz(SF) confers a modal length of 10 to 17 repeat units (RUs) to the O-antigen (Oag) component of lipopolysaccharide (LPS). PCPs form oligomeric structures believed to be related to their function. To identify functionally important regions within Wzz(SF), random in-frame linker mutagenesis was used to create mutants with 5-amino-acid insertions (termed Wzz(i) proteins), and DNA sequencing was used to locate the insertions. Analysis of the resulting LPS conferred by Wzz(i) proteins identified five mutant classes. The class I mutants were inactive, resulting in nonregulated LPS Oag chains, while classes II and III conferred shorter LPS Oag chains of 2 to 10 and 8 to 14 RUs, respectively. Class IV mutants retained near-wild-type function, and class V mutants increased the LPS Oag chain length to 16 to 25 RUs. In vivo formaldehyde cross-linking indicated class V mutants readily formed high-molecular-mass oligomers; however, class II and III Wzz(i) mutants were not effectively cross-linked. Wzz dimer stability was also investigated by heating cross-linked oligomers at 100 degrees C in the presence of SDS. Unlike the Wzz(SF) wild type and class IV and V Wzz(i) mutants, the class II and III mutant dimers were not detectable. The location of each insertion was mapped onto available PCP three-dimensional (3D) structures, revealing that class V mutations were most likely located within the inner cavity of the PCP oligomer. These data suggest that the ability to produce stable dimers may be important in determining Oag modal chain length.