Production and characterization of monoclonal antibodies against vaginolysin: Mapping of a region critical for its cytolytic activity

Transcriptomic and Proteomic Analysis of Gardnerella vaginalis Responding to Acidic pH and Hydrogen Peroxide Stress

Gardnerella vaginalis is the main pathogen that causes bacterial vaginosis. In the healthy vaginal microecological environment of a woman, the lactobacilli produce lactate and hydrogen peroxide to inhibit the growth of pathogens such as G. vaginalis. The lack of lactobacilli results in a high pH and low hydrogen peroxide in the vagina which facilitate G. vaginalis growth, leading to the imbalance of the vaginal microecology. In this study, lactate and hydrogen peroxide were added to a G. vaginalis culture medium to simulate the co-culture of the lactobacilli and G. vaginalis, and then the genes related to the stress response of G. vaginalis were identified using transcriptomics and proteomics. It was indicated that, among all the upregulated genes, most of them encoded transporters associated with the efflux of harmful substances, and the majority of the downregulated genes were related to the biofilm formation and epithelial cell adhesion. This study may help find new drug targets for G. vaginalis for the development of novel therapies for bacterial vaginosis.

Cross-reactive monoclonal antibodies against fish parvalbumins as a tool for studying antigenic similarity of different parvalbumins and analysis of fish extracts

Fish parvalbumins are heat-stable calcium-binding proteins that are highly cross-reactive in causing allergy symptoms in fish-sensitized patients. The reactivities of parvalbumin-specific monoclonal or polyclonal antibodies with parvalbumins of different fish species allowed their application for development of various immunoassays for allergen identification in fish samples. In this study, monoclonal antibodies (MAbs) were generated against two parvalbumins - natural Atlantic cod parvalbumin and recombinant common carp β-parvalbumin expressed in E. coli. Large collections of recombinant parvalbumins and natural allergen extracts of different fish species and other animals were used to identify the specificities of these MAbs using ELISA, Western blot, and dot blot. MAbs demonstrated different patterns of cross-reactivities with recombinant parvalbumins. Their binding affinities were affected by the addition and removal of Ca²⁺ ions. Moreover, all MAbs showed a broad reactivity with the target antigens in natural fish, chicken, and pork extracts. The ability of two MAbs (clones 7B2 and 3F6) to identify and isolate native parvalbumins from allergen extracts was confirmed by Western blot. Epitope mapping using recombinant fragments of Atlantic cod parvalbumin (Gad m 1) and common carp parvalbumin (Cyp c 1) revealed that 4 out of 5 MAbs recognize parvalbumin regions that contain calcium binding sites. In conclusion, the generated broadly reactive well-characterized MAbs against fish β-parvalbumins could be applied for investigation of parvalbumins of fish and other animals and their detection in allergen extracts.

Rapid Point-of-Care Test Kit for Bacterial Vaginosis: Detection of Vaginolysin and Clue Cells Using Paper Strips and a Smartphone

There is an unmet need for a point-of-care test that is accurate, affordable, and simple to diagnose bacterial vaginosis, the most common cause of vaginal symptoms among women. Bacterial vaginosis leaves patients with undesirable vaginal discharge, malodor, and discomfort. Currently, the diagnosis of bacterial vaginosis is inaccurate and complex, leading to high rates of misdiagnosis. Inaccurate diagnoses are unsafe as bacterial vaginosis increases the risks of acquiring sexually transmitted infections as well as the likelihood of miscarriages. To date, the most commonly identified bacteria associated with bacterial vaginosis is Gardnerella vaginalis. We developed a method for the expression, purification, and detection of vaginolysin, the most well-characterized virulence factor of G. vaginalis. Elevated levels of G. vaginalis have been shown to lead to a toxic vaginal environment, facilitating bacterial vaginosis. We have developed an enzyme-linked immunosorbent assay for the detection of vaginolysin, which was translated to a lateral flow assay for use in a rapid, straightforward, cost-effective paper-based diagnostic test for vaginolysin that does not require the use of instrumentation. In conjunction, we have employed a commercially available smartphone microscopy kit to visualize clue cells without the need for equipment or electricity. The combination of these methodologies allows for an accurate and easy approach to diagnose bacterial vaginosis with minimal resources for use in any setting.

Membrane Cholesterol Content and Lipid Organization Influence Melittin and Pneumolysin Pore-Forming Activity

Melittin, the main toxic component in the venom of the European honeybee, interacts with natural and artificial membranes due to its amphiphilic properties. Rather than interacting with a specific receptor, melittin interacts with the lipid components, disrupting the lipid bilayer and inducing ion leakage and osmotic shock. This mechanism of action is shared with pneumolysin and other members of the cholesterol-dependent cytolysin family. In this manuscript, we investigated the inverse correlation for cholesterol dependency of these two toxins. While pneumolysin-induced damage is reduced by pretreatment with the cholesterol-depleting agent methyl-β-cyclodextrin, the toxicity of melittin, after cholesterol depletion, increased. A similar response was also observed after a short incubation with lipophilic simvastatin, which alters membrane lipid organization and structure, clustering lipid rafts. Therefore, changes in toxin sensitivity can be achieved in cells by depleting cholesterol or changing the lipid bilayer organization.

Inhibitory Monoclonal Antibodies and Their Recombinant Derivatives Targeting Surface-Exposed Carbonic Anhydrase XII on Cancer Cells

Monoclonal and recombinant antibodies are widely used for the diagnostics and therapy of cancer. They are generated to interact with cell surface proteins which are usually involved in the development and progression of cancer. Carbonic anhydrase XII (CA XII) contributes to the survival of tumors under hypoxic conditions thus is considered a candidate target for antibody-based therapy. In this study, we have generated a novel collection of monoclonal antibodies (MAbs) against the recombinant extracellular domain of CA XII produced in HEK-293 cells. Eighteen out of 24 MAbs were reactive with cellular CA XII on the surface of live kidney and lung cancer cells as determined by flow cytometry. One MAb 14D6 also inhibited the enzymatic activity of recombinant CA XII as measured by the stopped-flow assay. MAb 14D6 showed the migrastatic effect on human lung carcinoma A549 and renal carcinoma A498 cell lines in a ‘wound healing’ assay. It did not reduce the growth of multicellular lung and renal cancer spheroids but reduced the cell viability by the ATP Bioluminescence assay. Epitope mapping revealed the surface-exposed amino acid sequence (35-FGPDGENS-42) close to the catalytic center of CA XII recognized by the MAb 14D6. The variable regions of the heavy and light chains of MAb 14D6 were sequenced and their complementarity-determining regions were defined. The obtained variable sequences were used to generate recombinant antibodies in two formats: single-chain fragment variable (scFv) expressed in E. coli and scFv fused to human IgG1 Fc fragment (scFv-Fc) expressed in Chinese Hamster Ovary (CHO) cells. Both recombinant antibodies maintained the same specificity for CA XII as the parental MAb 14D6. The novel antibodies may represent promising tools for CA XII-related cancer research and immunotherapy.

Mapping of Recognition Sites of Monoclonal Antibodies Responsible for the Inhibition of Pneumolysin Functional Activity

The pathogenicity of many bacteria, including Streptococcus pneumoniae, depends on pore-forming toxins (PFTs) that cause host cell lysis by forming large pores in cholesterol-containing cell membranes. Therefore, PFTs-neutralising antibodies may provide useful tools for reducing S. pneumoniae pathogenic effects. This study aimed at the development and characterisation of monoclonal antibodies (MAbs) with neutralising activity to S. pneumoniae PFT pneumolysin (PLY). Five out of 10 produced MAbs were able to neutralise the cytolytic activity of PLY on a lung epithelial cell line. Epitope mapping with a series of recombinant overlapping PLY fragments revealed that neutralising MAbs are directed against PLY loops L1 and L3 within domain 4. The epitopes of MAbs 3A9, 6E5 and 12F11 located at L1 loop (aa 454–471) were crucial for PLY binding to the immobilised cholesterol. In contrast, the MAb 12D10 recognising L3 (aa 403–423) and the MAb 3F3 against the conformational epitope did not interfere with PLY-cholesterol interaction. Due to conformation-dependent binding, the approach to use overlapping peptides for fine epitope mapping of the neutralising MAbs was unsuccessful. Therefore, the epitopes recognised by the MAbs were analysed using computational methods. This study provides new data on PLY sites involved in functional activity.

Cholesterol-Dependent Cytolysins Produced by Vaginal Bacteria: Certainties and Controversies

Bacterial vaginosis (BV) is a vaginal anaerobic dysbiosis that affects women of reproductive age worldwide. BV is microbiologically characterized by the depletion of vaginal lactobacilli and the overgrowth of anaerobic bacterial species. Accumulated evidence suggests that Gardnerella spp. have a pivotal role among BV-associated bacteria in the initiation and development of BV. However, Gardnerella spp. often colonize healthy women. Lactobacillus iners is considered as a prevalent constituent of healthy vaginal microbiota, and is abundant in BV. Gardnerella spp. and L. iners secrete the toxins vaginolysin (VLY) and inerolysin (INY), which have structural and activity features attributed to cholesterol-dependent cytolysins (CDCs). CDCs are produced by many pathogenic bacteria as virulence factors that participate in various stages of disease progression by forming lytic and non-lytic pores in cell membranes or via pore-independent pathways. VLY is expressed in the majority of Gardnerella spp. isolates; less is known about the prevalence of the gene that encodes INY. INY is a classical CDC; membrane cholesterol acts a receptor for INY. VLY uses human CD59 as its receptor, although cholesterol remains indispensable for VLY pore-forming activity. INY-induced damage of artificial membranes is directly dependent on cholesterol concentration in the bilayer, whereas VLY-induced damage occurs with high levels of membrane cholesterol (>40 mol%). VLY primarily forms membrane-embedded complete rings in the synthetic bilayer, whereas INY forms arciform structures with smaller pore sizes. VLY activity is high at elevated pH, which is characteristic of BV, whereas INY activity is high at more acidic pH, which is specific for a healthy vagina. Increased VLY levels in vaginal mucosa in vivo were associated with clinical indicators of BV. However, experimental evidence is lacking for the specific roles of VLY and INY in BV. The interplay between vaginal bacterial species affects the expression of the gene encoding VLY, thereby modulating the virulence of Gardnerella spp. This review discusses the current evidence for VLY and INY cytolysins, including their structures and activities, factors affecting their expression, and their potential impacts on the progression of anaerobic dysbiosis.

Inerolysin and vaginolysin, the cytolysins implicated in vaginal dysbiosis, differently impair molecular integrity of phospholipid membranes

The pore-forming toxins, inerolysin (INY) and vaginolysin (VLY), produced by vaginal bacteria Lactobacillus iners and Gardnerella vaginalis were studied using the artificial cholesterol-rich tethered bilayer membranes (tBLMs) by electrochemical techniques. The electrochemical impedance spectroscopy (EIS) of tBLMs attested for the toxin-induced impairment of the integrity of phospholipid membranes. This observation was in line with the atomic force microscopy data demonstrating formation of oligomeric protein assemblies in tBLMs. These assemblies exhibited different morphologies: VLY mostly formed complete rings, whereas INY produced arciform structures. We found that both EIS (membrane damage) and the surface plasmon resonance (protein binding) data obtained on tBLMs are in-line with the data obtained in human cell lysis experiments. EIS, however, is capable of capturing effects inaccessible for biological activity assays. Specifically, we found that the INY-induced damage of tBLMs is nearly a linear function of membrane cholesterol content, whereas VLY triggered significant damage only at high (50 mol%) cholesterol concentrations. The observed differences of INY and VLY activities on phospholipid membranes might have clinical importance: both toxin-producing bacteria have been found in healthy vagina and dysbiosis, suggesting the need for adaptation at different vaginal conditions. Our results broaden the possibilities of application of tBLMs in medical diagnostics.

Interaction of Gardnerella vaginalis and Vaginolysin with the Apical versus Basolateral Face of a Three-Dimensional Model of Vaginal Epithelium

Studies have implicated Gardnerella vaginalis as an important etiological agent in bacterial vaginosis (BV). It produces a cholesterol-dependent cytolysin, vaginolysin (VLY). In this study, we sought to characterize the interaction between vaginal epithelium, G. vaginalis, and VLY using EpiVaginal tissues from MatTek. These tissues are three-dimensional and have distinct apical and basolateral sides, enabling comparison of the effects of G. vaginalis and VLY following exposure to either side. We measured cytotoxicity, cytokine production, and bacterial growth, following apical versus basolateral exposure. G. vaginalis exhibited more-rapid growth in coculture with the tissue model when it was exposed to the apical side. VLY permeabilized cells on the basolateral side of the tissues but failed to permeabilize apical epithelial cells. Cytokine secretion in response to VLY and G. vaginalis also depended on the polarity of exposure. VLY did not cause significant changes in cytokine levels when exposed apically. Apical tissue challenge by G. vaginalis appeared to dampen the inflammatory response, as decreases in granulocyte-macrophage colony-stimulating factor (GM-CSF) (6.6-fold), RANTES (14.8-fold), and interferon gamma inducible protein 10 kDa (IP-10) (53-fold) and an increase in interleukin-1 receptor antagonist (IL-1ra) (5-fold) were observed. In vivo, G. vaginalis normally colonizes the apical face of the vaginal epithelium. Results from this study suggest that while G. vaginalis may grow on the apical face of the vaginal epithelium, its VLY toxin does not target these cells in this model. This phenomenon could have important implications regarding colonization of the vagina by G. vaginalis and may suggest an explanation for the lack of an overt immune response to this organism.

Phenotypic characterization of Gardnerella vaginalis subgroups suggests differences in their virulence potential

The well-known genotypic and phenotypic diversity of G. vaginalis resulted in its classification into at least four subgroups (clades) with diverse genomic properties. To evaluate the virulence potential of G. vaginalis subgroups, we analyzed the virulence-related phenotypic characteristics of 14 isolates of clade 1, 12 isolates of clade 2, 8 isolates of clade 4 assessing their in vitro ability to grow as a biofilm, produce the toxin vaginolysin, and express sialidase activity. Significant differences in VLY production were found (p = 0.023), but further analysis of clade pairs did not confirm this finding. The amount of biofim did not differ significantly among the clades. Analysis of sialidase activity indicated statistically significant differences among the clades (p < 0.001). Production of active recombinant G. vaginalis sialidase demonstrated the link between the sld gene and enzymatic activity, which may be differentially regulated at the transcriptional level. Statistical classification analysis (random forests algorithm) showed that G. vaginalis clades could be best defined by the profiles of two phenotypic characteristics: sialidase activity and vaginolysin production. The results of principal component analysis and hierarchical clustering suggested that all isolates can be subgrouped into three clusters, the structures of which are determined based on phenotypic characteristics of the isolates. Clade 4 was the most homogenous group, as all isolates were found in the same cluster, which is characterized by low production of all studied virulence factors. Clade 2 isolates were mainly distributed between two clusters, whereas clade 1 isolates were found in all three clusters that were characterized by a distinct profile of phenotypic characteristics. Our findings suggest that G. vaginalis subgroups with different virulence potential might play distinct roles in vaginal microbiota.

Generation in yeast and antigenic characterization of hepatitis E virus capsid protein virus-like particles

Hepatitis E is a globally distributed human disease caused by hepatitis E virus (HEV). In Europe, it spreads through undercooked pork meat or other products and with blood components through transfusions. There are no approved or golden standard serologic systems for HEV diagnostics. Commercially available HEV tests often provide inconsistent results which may differ among the assays. In this study, we describe generation in yeast and characterization of HEV genotype 3 (HEV-3) and rat HEV capsid proteins self-assembled into virus-like particles (VLPs) and the development of HEV-specific monoclonal antibodies (MAbs). Full-length HEV-3 and rat HEV capsid proteins and their truncated variants comprising amino acids (aa) 112-608 were produced in yeast S. cerevisiae. The yeast-expressed rat HEV capsid protein was found to be glycosylated. The full-length HEV-3 capsid protein and both full-length and truncated rat HEV capsid proteins were capable to self-assemble into VLPs. All recombinant proteins contained HEV genotype-specific linear epitopes and cross-reactive conformational epitopes recognized by serum antibodies from HEV-infected reservoir animals. Two panels of MAbs against HEV-3 and rat HEV capsid proteins were generated. Their cross-reactivity pattern was investigated by Western blot, ELISA, and immunofluorescence assay on HEV-3-infected cell cultures. The analysis revealed cross-reactive, genotype-specific, and virus-reactive MAbs. MAb epitopes were localized within S, M, and P domains of HEV-3 and rat HEV capsid proteins. Yeast-generated recombinant VLPs of HEV-3 and rat HEV capsid proteins and HEV-specific MAbs might be employed to develop novel HEV detection systems.

Gardnerella vaginalis bacteremia associated with severe acute encephalopathy in a young female patient

Gardnerella vaginalis is a facultative anaerobic bacterium that inhabits the genitourinary tract of both healthy women and those with bacterial vaginosis. We report a case of G. vaginalis bacteremia associated with severe toxic encephalopathy in a young woman. Anaerobic blood cultures yielded pure growth of small gram-variable rods later identified as G. vaginalis by both rapid biochemical tests and 16S rRNA gene sequencing. The patient recovered after treatment with amoxicillin-clavulanate according to the in vitro susceptibility testing. The complete genome of G. vaginalis isolate from blood cultures was determined. In vitro G. vaginalis isolate produced elevated amounts of a pore-forming toxin vaginolysin compared to control G. vaginalis isolates. We hypothesize that this toxin, if produced in high amounts in blood, is able to disrupt the blood-brain barrier and exert a toxic activity on brain cells.

Synthesis of human parainfluenza virus 4 nucleocapsid-like particles in yeast and their use for detection of virus-specific antibodies in human serum

The aim of this study was to produce human parainfluenza virus type 4 (HPIV4) nucleocapsid (N) protein in yeast Saccharomyces cerevisiae expression system, to explore its structural and antigenic properties and to evaluate its applicability in serology. The use of an optimized gene encoding HPIV4 N protein amino acid (aa) sequence GenBank AGU90031.1 allowed high yield of recombinant N protein forming nucleocapsid-like particles (NLPs) in yeast. A substitution L332D disrupted self-assembly of NLPs, confirming the role of this position in the N proteins of Paramyxovirinae. Three monoclonal antibodies (MAbs) were generated against the NLP-forming HPIV4 N protein. They recognised HPIV4-infected cells, demonstrating the antigenic similarity between the recombinant and virus-derived N proteins. HPIV4 N protein was used as a coating antigen in an indirect IgG ELISA with serum specimens of 154 patients with respiratory tract infection. The same serum specimens were tested with previously generated N protein of a closely related HPIV2, another representative of genus Rubulavirus. Competitive ELISA was developed using related yeast-produced viral antigens to deplete the cross-reactive serum antibodies. In the ELISA either without or with competition using heterologous HPIV (2 or 4) N or mumps virus N proteins, the seroprevalence of HPIV4 N-specific IgG was, respectively, 46.8, 39.6 and 40.3% and the seroprevalence of HPIV2 N-specific IgG-47.4, 39.0 and 37.7%. In conclusion, yeast-produced HPIV4 N protein shares structural and antigenic properties of the native virus nucleocapsids. Yeast-produced HPIV4 and HPIV2 NLPs are prospective tools in serology.

Structural Basis for Receptor Recognition by the Human CD59-Responsive Cholesterol-Dependent Cytolysins

Cholesterol-dependent cytolysins (CDCs) are a family of pore-forming toxins that punch holes in the outer membrane of eukaryotic cells. Cholesterol serves as the receptor, but a subclass of CDCs first binds to human CD59. Here we describe the crystal structures of vaginolysin and intermedilysin complexed to CD59. These studies, together with small-angle X-ray scattering, reveal that CD59 binds to each at different, though overlapping, sites, consistent with molecular dynamics simulations and binding studies. The CDC consensus undecapeptide motif, which for the CD59-responsive CDCs has a proline instead of a tryptophan in the motif, adopts a strikingly different conformation between the structures; our data suggest that the proline acts as a selectivity switch to ensure CD59-dependent CDCs bind their protein receptor first in preference to cholesterol. The structural data suggest a detailed model of how these water-soluble toxins assemble as prepores on the cell surface.

Tethered bilayer membranes as a complementary tool for functional and structural studies: The pyolysin case

We demonstrate the use of tethered bilayer lipid membranes (tBLMs) as an experimental platform for functional and structural studies of membrane associated proteins by electrochemical techniques. The reconstitution of the cholesterol-dependent cytolysin (CDC) pyolysin (PLO) from Trueperella pyogenes into tBLMs was followed in real-time by electrochemical impedance spectroscopy (EIS). Changes of the EIS parameters of the tBLMs upon exposure to PLO solutions were consistent with the dielectric barrier damage occurring through the formation of water-filled pores in membranes. Parallel experiments involving a mutant version of PLO, which is able to bind to the membranes but does not form oligomer pores, strengthen the reliability of this methodology, since no change in the electrochemical impedance was observed. Complementary atomic force microscopy (AFM) and neutron reflectometry (NR) measurements revealed structural details of the membrane bound PLO, consistent with the structural transformations of the membrane bound toxins found for other cholesterol dependent cytolysins. In this work, using the tBLMs platform we also observed a protective effect of the dynamin inhibitor Dynasore against pyolysin as well as pneumolysin. An effect of Dynasore in tBLMs, which was earlier observed in experiments with live cells, confirms the biological relevance of the tBLMs models, as well as demonstrates the potential of the electrochemical impedance spectroscopy to quantify membrane damage by the pore forming toxins. In conclusion, tBLMs are a reliable and complementary method to explore the activity of CDCs in eukaryotic cells and to develop strategies to limit the toxic effects of CDCs.

The cytolytic activity of vaginolysin strictly depends on cholesterol and is potentiated by human CD59

Gardnerella vaginalis produces cytolysin vaginolysin (VLY), which has been suggested to be a contributor to bacterial vaginosis pathogenesis. VLY along with intermedilysin (ILY) from Streptococcus intermedius have been attributed to a group of cholesterol-dependent cytolysins (CDCs) whose pore-forming activity depends on human CD59 (hCD59). Here, we show that different types of cells lacking hCD59 are susceptible to VLY-mediated lysis, albeit to different extents. We analyze the effects of both hCD59 and cholesterol on VLY cytolytic activity. We show that VLY binds to cholesterol-rich membranes of non-human cells, while VLY with an impaired cholesterol recognition site retains binding to the hCD59-containing cells. We further demonstrate that cholesterol binding by VLY is sufficient to trigger the formation of oligomeric complexes on cholesterol rich-liposomes lacking hCD59. Thus, VLY may induce cell lysis following two alternative pathways. One requires only cholesterol and does not depend on hCD59. The second pathway involves hCD59 contribution similarly to ILY. Apparently, under physiological conditions VLY acts in the most effective way by accepting the assistance of hCD59.

Monoclonal antibodies raised against 167-180 aa sequence of human carbonic anhydrase XII inhibit its enzymatic activity

Abstract Human carbonic anhydrase XII (CA XII) is a single-pass transmembrane protein with an extracellular catalytic domain. This enzyme is being recognized as a potential biomarker for different tumours. The current study was aimed to generate monoclonal antibodies (MAbs) neutralizing the enzymatic activity of CA XII. Bioinformatics analysis of CA XII structure revealed surface-exposed sequences located in a proximity of its catalytic centre. Two MAbs against the selected antigenic peptide spanning 167-180 aa sequence of CA XII were generated. The MAbs were reactive with recombinant catalytic domain of CA XII expressed either in E. coli or mammalian cells. Inhibitory activity of the MAbs was demonstrated by a stopped flow CO2 hydration assay. The study provides new data on the surface-exposed linear CA XII epitope that may serve as a target for inhibitory antibodies with a potential immunotherapeutic application.

Reconstitution of cholesterol-dependent vaginolysin into tethered phospholipid bilayers: implications for bioanalysis

Functional reconstitution of the cholesterol-dependent cytolysin vaginolysin (VLY) from Gardnerella vaginalis into artificial tethered bilayer membranes (tBLMs) has been accomplished. The reconstitution of VLY was followed in real-time by electrochemical impedance spectroscopy (EIS). Changes of the EIS parameters of the tBLMs upon exposure to VLY solutions were consistent with the formation of water-filled pores in the membranes. It was found that reconstitution of VLY is a strictly cholesterol-dependent, irreversible process. At a constant cholesterol concentration reconstitution of VLY occurred in a concentration-dependent manner, thus allowing the monitoring of VLY concentration and activity in vitro and opening possibilities for tBLM utilization in bioanalysis. EIS methodology allowed us to detect VLY down to 0.5 nM (28 ng/mL) concentration. Inactivation of VLY by certain amino acid substitutions led to noticeably lesser tBLM damage. Pre-incubation of VLY with the neutralizing monoclonal antibody 9B4 inactivated the VLY membrane damage in a concentration-dependent manner, while the non-neutralizing antibody 21A5 exhibited no effect. These findings demonstrate the biological relevance of the interaction between VLY and the tBLM. The membrane-damaging interaction between VLY and tBLM was observed in the absence of the human CD59 receptor, known to strongly facilitate the hemolytic activity of VLY. Taken together, our study demonstrates the applicability of tBLMs as a bioanalytical platform for the detection of the activity of VLY and possibly other cholesterol-dependent cytolysins.

Genetic and biochemical diversity of Gardnerella vaginalis strains isolated from women with bacterial vaginosis

Gardnerella vaginalis is considered a substantial player in the progression of bacterial vaginosis (BV). We analysed 17 G. vaginalis strains isolated from the genital tract of women diagnosed with BV to establish a potential link between genotypes/biotypes and the expression of virulence factors, vaginolysin (VLY) and sialidase, which are assumed to play a substantial role in the pathogenesis of BV. Amplified ribosomal DNA restriction analysis revealed two G. vaginalis genotypes. Gardnerella vaginalis isolates of genotype 2 appeared more complex than genotype 1 and were subdivided into three subtypes. Biochemical typing allowed us to distinguish four different biotypes. A great diversity of the level of VLY production among the isolates of G. vaginalis may be related to a different cytotoxicity level of the strains. We did not find any correlation between VLY production level and G. vaginalis genotype/biotype. In contrast, a link between G. vaginalis genotype and sialidase production was established. Our findings on the diversity of VLY expression level in different clinical isolates and linking sialidase activity with the genotype of G. vaginalis could help to evaluate the pathogenic potential of different G. vaginalis strains.

Production in yeast of pseudotype virus-like particles harboring functionally active antibody fragments neutralizing the cytolytic activity of vaginolysin

Background

Recombinant antibodies can be produced in different formats and different expression systems. Single chain variable fragments (scFvs) represent an attractive alternative to full-length antibodies and they can be easily produced in bacteria or yeast. However, the scFvs exhibit monovalent antigen-binding properties and short serum half-lives. The stability and avidity of the scFvs can be improved by their multimerization or fusion with IgG Fc domain. The aim of the current study was to investigate the possibilities to produce in yeast high-affinity scFv-Fc proteins neutralizing the cytolytic activity of vaginolysin (VLY), the main virulence factor of Gardnerella vaginalis.

Results

The scFv protein derived from hybridoma cell line producing high-affinity neutralizing antibodies against VLY was fused with human IgG1 Fc domain. Four different variants of anti-VLY scFv-Fc fusion proteins were constructed and produced in yeast Saccharomyces cerevisiae. The non-tagged scFv-Fc and hexahistidine-tagged scFv-Fc proteins were found predominantly as insoluble aggregates and therefore were not suitable for further purification and activity testing. The addition of yeast α-factor signal sequence did not support secretion of anti-VLY scFv-Fc but increased the amount of its intracellular soluble form. However, the purified protein showed a weak VLY-neutralizing capability. In contrast, the fusion of anti-VLY scFv-Fc molecules with hamster polyomavirus-derived VP2 protein and its co-expression with VP1 protein resulted in an effective production of pseudotype virus-like particles (VLPs) that exhibited strong VLY-binding activity. Recombinant scFv-Fc molecules displayed on the surface of VLPs neutralized VLY-mediated lysis of human erythrocytes and HeLa cells with high potency comparable to that of full-length antibody.

Conclusions

Recombinant scFv-Fc proteins were expressed in yeast with low efficiency. New approach to display the scFv-Fc molecules on the surface of pseudotype VLPs was successful and allowed generation of multivalent scFv-Fc proteins with high VLY-neutralizing potency. Our study demonstrated for the first time that large recombinant antibody molecule fused with hamster polyomavirus VP2 protein and co-expressed with VP1 protein in the form of pseudotype VLPs was properly folded and exhibited strong antigen-binding activity. The current study broadens the potential of recombinant VLPs as a highly efficient carrier for functionally active complex proteins.

Generation of recombinant single-chain antibodies neutralizing the cytolytic activity of vaginolysin, the main virulence factor of Gardnerella vaginalis

Background

Gardnerella vaginalis is identified as the predominant colonist of the vaginal tract in women with bacterial vaginosis. Vaginolysin (VLY) is a protein toxin released by G. vaginalis. VLY possesses cytolytic activity and is considered as a main virulence factor of G. vaginalis. Inhibition of VLY-mediated cell lysis by antibodies may have important physiological relevance.

Results

Single-chain variable fragments of immunoglobulins (scFvs) were cloned from two hybridoma cell lines producing neutralizing antibodies against VLY and expressed as active proteins in E. coli. For each hybridoma, two variants of anti-VLY scFv consisting of either VL-VH or VH-VL linked with a 20 aa-long linker sequence (G₄S)₄ were constructed. Recovery of scFvs from inclusion bodies with subsequent purification by metal-chelate chromatography resulted in VLY-binding proteins that were predominantly monomeric. The antigen-binding activity of purified scFvs was verified by an indirect ELISA. The neutralizing activity was investigated by in vitro hemolytic assay and cytolytic assay using HeLa cell line. Calculated apparent K_d values and neutralizing potency of scFvs were in agreement with those of parental full-length antibodies. VH-VL and VL-VH variants of scFvs showed similar affinity and neutralizing potency. The anti-VLY scFvs derived from hybridoma clone 9B4 exhibited high VLY-neutralizing activity both on human erythrocytes and cervical epithelial HeLa cells.

Conclusions

Hybridoma-derived scFvs with VLY-binding activity were expressed in E. coli. Recombinant anti-VLY scFvs inhibited VLY-mediated cell lysis. The monovalent scFvs showed reduced affinity and neutralizing potency as compared to the respective full-length antibodies. The loss of avidity could be restored by generating scFv constructs with multivalent binding properties. Generated scFvs is the first example of recombinant single-chain antibodies with VLY-neutralizing activity produced in prokaryote expression system. G. vaginalis caused infections continue to be a world-wide problem, therefore neutralizing recombinant antibodies may provide novel therapeutic agents useful in the treatment of bacterial vaginosis and other diseases caused by G. vaginalis.

Preparation and identification of monoclonal antibody against abrin-a

BALB/c mice were immunized four times with formalin-prepared abrin-a. Using the polyethylene glycol method, immunized splenocytes were isolated and fused with SP2/0 cells. An indirect ELISA was established and used to detect positive clones secreting monoclonal antibodies (mAbs) against abrin-a. After analysis, three hybridoma clones secreting IgG-subtype mAbs were obtained. The antibodies were purified from the hybridoma growth medium using protein A or G affinity chromatography. Western blot analysis was used to analyze the antigenic epitopes on abrin-a recognized by the mAbs. The mAbs were specific for abrin-a, with no detectable cross-reactivity with several homologous toxins and associated agglutinins. Sandwich ELISA was then developed using these mAbs, which had a detection limit for abrin-a of 7.8 ng/mL.

Comparative genomics of Gardnerella vaginalis strains reveals substantial differences in metabolic and virulence potential

BACKGROUND

Gardnerella vaginalis is described as a common vaginal bacterial species whose presence correlates strongly with bacterial vaginosis (BV). Here we report the genome sequencing and comparative analyses of three strains of G. vaginalis. Strains 317 (ATCC 14019) and 594 (ATCC 14018) were isolated from the vaginal tracts of women with symptomatic BV, while Strain 409-05 was isolated from a healthy, asymptomatic individual with a Nugent score of 9.

PRINCIPAL FINDINGS

Substantial genomic rearrangement and heterogeneity were observed that appeared to have resulted from both mobile elements and substantial lateral gene transfer. These genomic differences translated to differences in metabolic potential. All strains are equipped with significant virulence potential, including genes encoding the previously described vaginolysin, pili for cytoadhesion, EPS biosynthetic genes for biofilm formation, and antimicrobial resistance systems, We also observed systems promoting multi-drug and lantibiotic extrusion. All G. vaginalis strains possess a large number of genes that may enhance their ability to compete with and exclude other vaginal colonists. These include up to six toxin-antitoxin systems and up to nine additional antitoxins lacking cognate toxins, several of which are clustered within each genome. All strains encode bacteriocidal toxins, including two lysozyme-like toxins produced uniquely by strain 409-05. Interestingly, the BV isolates encode numerous proteins not found in strain 409-05 that likely increase their pathogenic potential. These include enzymes enabling mucin degradation, a trait previously described to strongly correlate with BV, although commonly attributed to non-G. vaginalis species.

CONCLUSIONS

Collectively, our results indicate that all three strains are able to thrive in vaginal environments, and therein the BV isolates are capable of occupying a niche that is unique from 409-05. Each strain has significant virulence potential, although genomic and metabolic differences, such as the ability to degrade mucin, indicate that the detection of G. vaginalis in the vaginal tract provides only partial information on the physiological potential of the organism.