Acinetobacter baumannii—a leading cause of nosocomial infections—has a remarkable capacity to persist in hospital environments and medical devices due to its ability to form biofilms. Biofilm ...formation is mediated by Csu pili, assembled via the “archaic” chaperone–usher pathway. The X-ray structure of the CsuC-CsuE chaperone–adhesin preassembly complex reveals the basis for bacterial attachment to abiotic surfaces. CsuE exposes three hydrophobic finger-like loops at the tip of the pilus. Decreasing the hydrophobicity of these abolishes bacterial attachment, suggesting that archaic pili use tip-fingers to detect and bind to hydrophobic cavities in substrates. Antitip antibody completely blocks biofilm formation, presenting a means to prevent the spread of the pathogen. The use of hydrophilic materials instead of hydrophobic plastics in medical devices may represent another simple and cheap solution to reduce pathogen spread. Phylogenetic analysis suggests that the tip-fingers binding mechanism is shared by all archaic pili carrying two-domain adhesins. The use of flexible fingers instead of classical receptor-binding cavities is presumably more advantageous for attachment to structurally variable substrates, such as abiotic surfaces.
The BabA adhesin mediates high-affinity binding of Helicobacter pylori to the ABO blood group antigen-glycosylated gastric mucosa. Here we show that BabA is acid responsive—binding is reduced at low ...pH and restored by acid neutralization. Acid responsiveness differs among strains; often correlates with different intragastric regions and evolves during chronic infection and disease progression; and depends on pH sensor sequences in BabA and on pH reversible formation of high-affinity binding BabA multimers. We propose that BabA’s extraordinary reversible acid responsiveness enables tight mucosal bacterial adherence while also allowing an effective escape from epithelial cells and mucus that are shed into the acidic bactericidal lumen and that bio-selection and changes in BabA binding properties through mutation and recombination with babA-related genes are selected by differences among individuals and by changes in gastric acidity over time. These processes generate diverse H. pylori subpopulations, in which BabA’s adaptive evolution contributes to H. pylori persistence and overt gastric disease.
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•H. pylori adherence is acid sensitive and fully reversed by increased pH•Diversity in BabA adhesin's acid sensitivity is driven by inflammation and disease progression•pH sensor sequences in BabA’s binding domains determine its pH responsiveness•BabA adaptation to mucosal atrophy and elevated pH can contribute to gastric cancer
Helicobacter pylori binds with high affinity to ABO/Leb blood group antigens to persist in the stomach mucosa. Bugaytsova et al. show that adherence is acid sensitive, fully reversed when acidity is decreased, and controlled by BabA adhesin protein's pH-sensors sequences changes in which are selected during chronic infection and disease.
Significance Serogroup B meningococcus (MenB) causes severe sepsis and invasive meningococcal disease, particularly affecting young children and adolescents. The genome-derived vaccine 4CMenB that ...targets MenB, has now been approved in over 30 countries worldwide. Here we report the crystal structure of the trimeric autotransporter Neisserial adhesin A (NadA), one of the three protein antigens included in 4CMenB, and the epitope mapping of a bactericidal mAb monoclonal antibody that targets the functional head domain of NadA. These results provide important insights into the structure and vaccine-induced immune response of this meningococcal antigen and may inform the engineering of improved immunogens by structure-based design.
Serogroup B Neisseria meningitidis (MenB) is a major cause of severe sepsis and invasive meningococcal disease, which is associated with 5–15% mortality and devastating long-term sequelae. Neisserial adhesin A (NadA), a trimeric autotransporter adhesin (TAA) that acts in adhesion to and invasion of host epithelial cells, is one of the three antigens discovered by genome mining that are part of the MenB vaccine that recently was approved by the European Medicines Agency. Here we present the crystal structure of NadA variant 5 at 2 Å resolution and transmission electron microscopy data for NadA variant 3 that is present in the vaccine. The two variants show similar overall topology with a novel TAA fold predominantly composed of trimeric coiled-coils with three protruding wing-like structures that create an unusual N-terminal head domain. Detailed mapping of the binding site of a bactericidal antibody by hydrogen/deuterium exchange MS shows that a protective conformational epitope is located in the head of NadA. These results provide information that is important for elucidating the biological function and vaccine efficacy of NadA.
Bovine mycoplasmosis is an important infectious disease of cattle caused by
(
) which poses a serious threat to the breeding industry. Adhesin is involved in the initial process of
colonization, ...which is closely related to the infection, cell invasion, immune escape and virulence of this pathogenic microorganism. For the reason that
lacks a cell wall, its adhesin is predominantly located on the surface of the cell membrane. The adhesins of
are usually identified by adhesion and adhesion inhibition analysis, and more than 10 adhesins have been identified so far. These adhesins primarily bind to plasminogen, fibronectin, heparin and amyloid precursor-like protein-2 of host cells. This review aims to concisely summarize the current knowledge regarding the adhesins of
and their target proteins of the host cell. Additionally, the biological characteristics of the adhesin will be briefly analyzed.
Most core residues of coiled coils are hydrophobic. Occasional polar residues are thought to lower stability, but impart structural specificity. The coiled coils of trimeric autotransporter adhesins ...(TAAs) are conspicuous for their large number of polar residues in position d of the core, which often leads to their prediction as natively unstructured regions. The most frequent residue, asparagine (N@d), can occur in runs of up to 19 consecutive heptads, frequently in the motif I/VxxNTxx. In the Salmonella TAA, SadA, the core asparagines form rings of interacting residues with the following threonines, grouped around a central anion. This conformation is observed generally in N@d layers from trimeric coiled coils of known structure. Attempts to impose a different register on the motif show that the asparagines orient themselves specifically into the core, even against conflicting information from flanking domains. When engineered into the GCN4 leucine zipper, N@d layers progressively destabilized the structure, but zippers with 3 N@d layers still folded at high concentration. We propose that N@d layers maintain the coiled coils of TAAs in a soluble, export-competent state during autotransport through the outer membrane. More generally, we think that polar motifs that are both periodic and conserved may often reflect special folding requirements, rather than an unstructured state of the mature proteins.
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•Bacteria use adhesive proteins to bind host cell receptors to cause infection.•Both fast and strong binding is mediated by a switch in the adhesin conformation.•The conformational ...switch involves allosteric activation of the adhesive domain.•The allosteric activation requires separation from the anchoring domain.•The domain separation is the basis of ‘catch bonds’ but also occurs without force.
The FimH protein of Escherichia coli is a model two-domain adhesin that is able to mediate an allosteric catch bond mechanism of bacterial cell attachment, where the mannose-binding lectin domain switches from an ‘inactive’ conformation with fast binding to mannose to an ‘active’ conformation with slow detachment from mannose. Because mechanical tensile force favors separation of the domains and, thus, FimH activation, it has been thought that the catch bonds can only be manifested in a fluidic shear-dependent mode of adhesion. Here, we used recombinant FimH variants with a weakened inter-domain interaction and show that a fast and sustained allosteric activation of FimH can also occur under static, non-shear conditions. Moreover, it appears that lectin domain conformational activation happens intrinsically at a constant rate, independently from its ability to interact with the pilin domain or mannose. However, the latter two factors control the rate of FimH deactivation. Thus, the allosteric catch bond mechanism can be a much broader phenomenon involved in both fast and strong cell-pathogen attachments under a broad range of hydrodynamic conditions. This concept that allostery can enable more effective receptor-ligand interactions is fundamentally different from the conventional wisdom that allostery provides a mechanism to turn binding off under specific conditions.
Arg-gingipain A (RgpA) is the primary virulence factor of Porphyromonas gingivalis and contains hemagglutinin adhesin (HA), which helps bacteria adhere to cells and proteins. Hemagglutinin's ...functional domains include cleaved adhesin (CA), which acts as a hemagglutination and hemoglobin-binding actor. Here, we confirmed that the HA and CA genes are immunogenic, and using adjuvant chemokine to target dendritic cells (DCs) enhanced protective autoimmunity against P. gingivalis-induced periodontal disease.
C57 mice were immunized prophylactically with pVAX1-CA, pVAX1-HA, pVAX1, and phosphate-buffered saline (PBS) through intramuscular injection every 2 weeks for a total of three administrations before P. gingivalis-induced periodontitis. The DCs were analyzed using flow cytometry and ribonucleic acid sequencing (RNA-seq) transcriptomic assays following transfection with CA lentivirus. The efficacy of the co-delivered molecular adjuvant CA DNA vaccine was evaluated in vivo using flow cytometry, immunofluorescence techniques, and micro-computed tomography.
After the immunization, both the pVAX1-CA and pVAX1-HA groups exhibited significantly elevated P. gingivalis-specific IgG and IgG1, as well as a reduction in bone loss around periodontitis-affected teeth, compared to the pVAX1 and PBS groups (p < 0.05). The expression of CA promoted the secretion of HLA, CD86, CD83, and DC-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) in DCs. Furthermore, the RNA-seq analysis revealed a significant increase in the chemokine (C-C motif) ligand 19 (p < 0.05). A notable elevation in the quantities of DCs co-labeled with CD11c and major histocompatibility complex class II, along with an increase in interferon-gamma (IFN-γ) cells, was observed in the inguinal lymph nodes of mice subjected to CCL19-CA immunization. This outcome effectively illustrated the preservation of peri-implant bone mass in rats afflicted with P. gingivalis-induced peri-implantitis (p < 0.05).
The co-administration of a CCL19-conjugated CA DNA vaccine holds promise as an innovative and targeted immunization strategy against P. gingivalis-induced periodontitis and peri-implantitis.
The bacterionanofiber protein AtaA, a member of the trimeric autotransporter adhesin family found in Acinetobacter sp. Tol 5, is responsible for the nonspecific, high adhesiveness and ...autoagglutination of this strain. Previously, we introduced the ataA gene into the nonadhesive Acinetobacter strain ST-550, which conferred high adhesiveness to this strain, immobilized its cells, and improved indigo productivity due to enhanced tolerance to the toxic substrate. In this study, we again demonstrated the effectiveness of this new microbial immobilization method using AtaA in a number of conditions. AtaA enabled the effective immobilization of growing, resting, and lyophilized cells of a type strain of Acinetobacter, ADP1, which is also intrinsically nonadhesive, onto the surface of several kinds of support ranging from artificial to natural materials and from hydrophobic polyurethane to hydrophilic glass. Immobilization with AtaA enabled exclusive cell growth in the support space and only a few cells existed in the bulk medium. Immobilization of resting cells drastically increased cell concentration, depending on the support material; dry cells of approximately 110 g/L could be immobilized onto glass wool. Finally, we demonstrated that ADP1 cells immobilized on polyurethane foam can undergo at least 10 repetitive reactions without inactivation during a 5-h period. Even after drying and storing for 3 days, the immobilized cells showed enzymatic activity and an ester hydrolysis reaction was repeated by simply transferring the support with the cells into a fresh reaction buffer.
Cyclic diguanylate (c-di-GMP) is a second messenger that regulates the transition from motile to sessile lifestyles in numerous bacteria and controls virulence factor production in a variety of ...pathogens. In
, c-di-GMP negatively regulates flagellum biosynthesis and swimming motility and promotes the production of type IV pili (TFP), biofilm formation, and surface motility
Flagella have been identified as colonization factors in
, but the role of TFP in adherence to host cells and in colonization of the mammalian gut is unknown. Here we show that c-di-GMP promotes adherence to epithelial cells
, which can be partly attributed to the loss of flagella. Using TFP-null mutants, we demonstrate that adherence to epithelial cells is partially mediated by TFP and that this TFP-mediated adherence requires c-di-GMP regulation. In a mouse model of colonization, the TFP-null mutants initially colonized the intestine as well as the parental strain but were cleared more quickly. Moreover, compared to the parent strain,
strains lacking TFP were particularly deficient in association with the cecal mucosa. Together these data indicate that TFP and their positive regulation by c-di-GMP promote attachment of
to the intestinal epithelium and contribute to persistence of
in the host intestine.
Aims
The aims of this study were to develop an effective oral vaccine against enterotoxigenic Escherichia coli (ETEC) infection and to design new and more versatile mucosal adjuvants.
Methods and ...Results
Genetically engineered Lactobacillus casei strains expressing F4 (K88) fimbrial adhesin FaeG (rLpPG‐2‐FaeG) and either co‐expressing heat‐labile enterotoxin A (LTA) subunit with an amino acid mutation associated with reduced virulence (LTAK63) and a heat‐labile enterotoxin B (LTB) subunit of E. coli (rLpPG‐2‐LTAK63‐co‐LTB) or fused‐expressing LTAK63 and LTB (rLpPG‐2‐LTAK63‐fu‐LTB) were constructed. The immunogenicity of rLpPG‐2‐FaeG in conjunction with rLpPG‐2‐LTAK63‐co‐LTB or rLpPG‐2‐LTAK63‐fu‐LTB as an orally administered mucosal adjuvant in mice was evaluated. Results showed that the levels of FaeG‐specific serum IgG and mucosal sIgA, as well as the proliferation of lymphocytes, were significantly higher in mice orally co‐administered rLpPG‐2‐FaeG and rLpPG‐2‐LTAK63‐fu‐LTB compared with those administered rLpPG‐2‐FaeG alone, and were lower than those co‐administered rLpPG‐2‐FaeG and rLpPG‐2‐LTAK63‐co‐LTB. Moreover, effective protection was observed after challenge with F4+ ETEC strain CVCC 230 in mice co‐administered rLpPG‐2‐FaeG and rLpPG‐2‐LTAK63‐co‐LTB or rLpPG‐2‐FaeG and rLpPG‐2‐LTAK63‐fu‐LTB group compared with those that received rLpPG‐2‐FaeG alone.
Conclusions
rLpPG‐2‐FaeG showed greater immunogenicity in combination with LTAK63 and LTB as molecular adjuvants.
Significance and Impact of the Study
Recombinant Lactobacillus provides a promising platform for the development of vaccines against F4+ ETEC infection.
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