Structural insights into the extracytoplasmic thiamine-binding lipoprotein p37 of Mycoplasma hyorhinis

Improved transformation efficiency in Mycoplasma hominis enables disruption of the MIB-MIP system targeting human immunoglobulins

The pathogenicity of Mycoplasma hominis is poorly understood, mainly due to the absence of efficient genetic tools. A polyethylene glycol-mediated transformation protocol was recently developed for the M. hominis reference strain M132 using the pMT85-Tet plasmid. The transformation efficiency remained low, hampering generation of a large mutant library. In this study, we improved transformation efficiency by designing M. hominis-specific pMT85 derivatives. Using the Gibson Assembly, the Enterococcus-derived tet(M) gene of the pMT85-Tet plasmid was replaced by that of a M. hominis clinical isolate. Next, the Spiroplasma-derived spiralin gene promoter driving tet(M) expression was substituted by one of three putative regulatory regions (RRs): the M. hominis arginine deiminase RR, the M. hominis elongation factor Tu RR, or the 68 bp SynMyco synthetic RR. SynMyco-based construction led to a 100-fold increase in transformation efficiency in M. hominis M132. This construct was also transformed into the M. hominis PG21 reference strain and three other clinical isolates. The transposon insertion locus was determined for 128 M132-transformants. The majority of the impacted coding sequences encoded lipoproteins and proteins involved in DNA repair or in gene transfer. One transposon integration site was in the mycoplasma immunoglobulin protease gene. Phenotypic characterization of the mutant showed complete disruption of the human antibody cleavage ability of the transformant. These results demonstrate that our M. hominis-optimized plasmid can be used to generate large random transposon insertion libraries, enabling future studies of the pathogenicity of M. hominis. IMPORTANCE Mycoplasma hominis is an opportunistic human pathogen, whose physiopathology is poorly understood and for which genetic tools for transposition mutagenesis have been unavailable for years. A PEG-mediated transformation protocol was developed using the pMT85-Tet plasmid, but the transformation efficiency remained low. We designed a modified pMT85-Tet plasmid suitable for M. hominis. The use of a synthetic regulatory region upstream of the antibiotic resistance marker led to a 100-fold increase in the transformation efficiency. The generation and characterization of large transposon mutagenesis mutant libraries will provide insight into M. hominis pathogenesis. We selected a transformant in which the transposon was integrated in the locus encoding the immunoglobulin cleavage system MIB-MIP. Phenotypic characterization showed that the wild-type strain has a functional MIB-MIP system, whereas the mutant strain had lost the ability to cleave human immunoglobulins.

Identification of specific B cell linear epitopes of mycoplasma hyorhinis P37 protein using monoclonal antibodies against baculovirus-expressed P37 protein

BACKGROUND

Mycoplasma hyorhinis (Mhr) is the etiologic agent of lameness and polyserositis in swine. P37 is a membrane protein of Mhr that may be an important immunogen and is a potential target for diagnostic development. However, there is little information concerning Mhr P37 protein epitopes. A precise analysis of the P37 protein epitopes should extend our understanding of the antigenic composition of the P37 protein and the humoral immune responses to Mhr infection. Investigating the epitopes of Mhr P37 will help to establish a detection method for Mhr in tissue and provide an effective tool for detecting Mhr infection.

RESULTS

Western blot and indirect immunofluorescence assays (IFA) confirmed that the expressed P37 protein was recognized by Mhr-positive porcine and mouse sera. Furthermore, the P37 protein was purified using affinity chromatography and used to immunize mice for hybridoma cell fusion. Four monoclonal antibodies (mAbs) found to be positive for Mhr were detected in infected lung tissue. A panel of truncated P37 proteins was used to identify the minimal B cell linear epitopes of the protein based on these mAbs. The core epitope was determined to be ²⁰⁶KIKKAWNDKDWNTFRNF²²²_. CONCLUSIONS: In this study, we identified 17 critical amino acids that determine the epitope of the P37 protein of Mhr. This study identified mAbs that could provide useful tools for investigating the Mhr P37 antigenic core epitope (amino acids 206-222) and detecting Mhr-specific antigens in infected tissue.

Essential metabolism for a minimal cell

JCVI-syn3A, a robust minimal cell with a 543 kbp genome and 493 genes, provides a versatile platform to study the basics of life. Using the vast amount of experimental information available on its precursor, Mycoplasma mycoides capri, we assembled a near-complete metabolic network with 98% of enzymatic reactions supported by annotation or experiment. The model agrees well with genome-scale in vivo transposon mutagenesis experiments, showing a Matthews correlation coefficient of 0.59. The genes in the reconstruction have a high in vivo essentiality or quasi-essentiality of 92% (68% essential), compared to 79% in silico essentiality. This coherent model of the minimal metabolism in JCVI-syn3A at the same time also points toward specific open questions regarding the minimal genome of JCVI-syn3A, which still contains many genes of generic or completely unclear function. In particular, the model, its comparison to in vivo essentiality and proteomics data yield specific hypotheses on gene functions and metabolic capabilities; and provide suggestions for several further gene removals. In this way, the model and its accompanying data guide future investigations of the minimal cell. Finally, the identification of 30 essential genes with unclear function will motivate the search for new biological mechanisms beyond metabolism.

One way that researchers can test whether they understand a biological system is to see if they can accurately recreate it as a computer model. The more they learn about living things, the more the researchers can improve their models and the closer the models become to simulating the original. In this approach, it is best to start by trying to model a simple system.

Biologists have previously succeeded in creating ‘minimal bacterial cells’. These synthetic cells contain fewer genes than almost all other living things and they are believed to be among the simplest possible forms of life that can grow on their own. The minimal cells can produce all the chemicals that they need to survive – in other words, they have a metabolism. Accurately recreating one of these cells in a computer is a key first step towards simulating a complete living system.

Breuer et al. have developed a computer model to simulate the network of the biochemical reactions going on inside a minimal cell with just 493 genes. By altering the parameters of their model and comparing the results to experimental data, Breuer et al. explored the accuracy of their model. Overall, the model reproduces experimental results, but it is not yet perfect. The differences between the model and the experiments suggest new questions and tests that could advance our understanding of biology. In particular, Breuer et al. identified 30 genes that are essential for life in these cells but that currently have no known purpose.

Continuing to develop and expand models like these to reproduce more complex living systems provides a tool to test current knowledge of biology. These models may become so advanced that they could predict how living things will respond to changing situations. This would allow scientists to test ideas sooner and make much faster progress in understanding life on Earth. Ultimately, these models could one day help to accelerate medical and industrial processes to save lives and enhance productivity.

A p37-based ELISA used to monitor anti- Mycoplasma hyorhinis IgG in serum from pigs immunized with inactivated M. hyorhinis vaccines

Mycoplasma hyorhinis is an important pathogen of swine that can often occur as a respiratory coinfection with viral pathogens, but can also cause arthritis and polyserositis in infected animals. To date, no assay is available to assess the serologic response to M. hyorhinis vaccines, to our knowledge. We used recombinantly expressed M. hyorhinis p37 protein to monitor the magnitude of the IgG response in vaccinated animals. The assay was able to distinguish animals vaccinated with M. hyorhinis from those vaccinated with the other important Mycoplasma species: M. hyopneumoniae and M. hyosynoviae. When formulated with an ideal adjuvant, inactivated vaccines designed to protect animals against M. hyorhinis induced a measurable and dose-dependent antibody response against the p37 protein. Additionally, the protein appears to be highly conserved between strains of M. hyorhinis isolated in the United States. The specificity of the assay as well as the conservation and immunogenicity of the p37 protein make it an ideal candidate antigen for use in measuring the immune response against M. hyorhinis after vaccination in weaned pigs.

Mycoplasma-associated multidrug resistance of hepatocarcinoma cells requires the interaction of P37 and Annexin A2

Mycoplasma infection has been reported to be associated with cancer migration, invasion, epithelial-mesenchymal transition as well as the resistance to nucleoside analogues chemotherapeutic drugs. In this study, we found that the sensitivity of hepatocarcinoma cells to Cisplatin, Gemcitabine and Mitoxantrone was increased by mycoplasma elimination. Similar to the effect of anti-mycoplasma agent, interrupting the interaction between Mycoplasma hyorhinis membrane protein P37 and Annexin A2 of host cells using the N-terminal of ANXA2 polypeptide enhanced the sensitivity of HCC97L cells to Gemcitabine and Mitoxantrone. Meanwhile, we did not observe any changes in expression or distribution of multidrug resistance associated transporters, ATP-Binding Cassette protein B1, C1 and G2, on the removal of mycoplasma. These results suggest that mycoplasma induces a resistance to multiple drugs in hepatocarcinoma cells which required the interaction of P37 and Annexin A2. The pathway downstream this interaction needs to be explored.

Mapping of a Mycoplasma-Neutralizing Epitope on the Mycoplasmal p37 Protein

Many studies have shown that the mycoplasmal membrane protein p37 enhances cancer cell migration, invasion, and metastasis. Previously, we generated 6 monoclonal antibodies (MAbs) against the mycoplasmal protein p37 and showed the presence of mycoplasma-infected circulating tumor cells in the blood of hepatocellular carcinoma patients by using CA27, one of the six MAbs. When mycoplasmas were incubated with cancer cells in the presence of CA27, mycoplasma infection was completely inhibited, suggesting that CA27 is a neutralizing antibody inhibiting mycoplasma infection. To examine the neutralizing epitope of CA27, we generated a series of glutathione S-transferase (GST)-fused p37 deletion mutant proteins in which p37 was partly deleted. To express p37-coding sequences in E.coli, mycoplasmal TGA codons were substituted with TGG in the p37 deletion mutant genes. GST-fused p37 deletion mutant proteins were then screened to identify the epitope targeted by CA27. Western blots showed that CA27 bound to the residues 216–246 on the middle part of the p37 protein while it did not bind to the residues 183–219 and 216–240. Fine mapping showed that CA27 was able to bind to the residues 226–246, but its binding activity was relatively weakened as compared to that to the residues 216–246, suggesting that the residues 226–246 is essential for optimal binding activity of CA27. Interestingly, the treatment of the purified GST-tagged epitopes with urea showed that CA27 binding to the epitope was sodium dodecyl sulfate-resistant but urea-sensitive. The same 226–246 residues were also recognized by two other anti-p37 MAbs, suggesting that the epitope is immunodominant. The identification of the novel neutralizing epitope may provide new insight into the interaction between the p37 protein and host receptors.

Surface lipoproteome of Mycoplasma hominis PG21 and differential expression after contact with human dendritic cells

Aim: To assess the lipoproteins that are involved in the interaction between Mycoplasma hominis and human dendritic cells. Materials & methods: The surface lipoproteome of M. hominis PG21 was characterized by using Triton X-114 extraction and LC–MS/MS identification. The transcriptional changes in lipoprotein genes upon contact with human dendritic cells were determined by using reverse transcription quantitative PCR after identification of reference genes suitable for normalization. Results: A large-scale overexpression of lipoprotein genes was observed with 21 upregulated transcripts. Seven genes of unknown function were M. hominis species specific and six genes were putatively associated with increased nutrient capture from the host cell and adhesion. Conclusion: M. hominis regulates lipoprotein gene expression and may use species-specific mechanisms during the host colonization process.

Complete Genome Sequence of Mycoplasma hominis Strain Sprott (ATCC 33131), Isolated from a Patient with Nongonococcal Urethritis

Presented here is the complete and annotated genome sequence of Mycoplasma hominis Sprott (ATCC 33131). The chromosome comprises 695,214 bp, which is approximately 30 kb larger than the syntenic genome of M. hominis PG21(T). Tetracycline resistance of strain Sprott is most probably conferred by the tetM determinant, harbored on a mosaic transposon-like structure.

Activation of EGFR-PI3K-AKT signaling is required for Mycoplasma hyorhinis-promoted gastric cancer cell migration

Persistent infection of Mycoplasma hyorhinis (M. hyorhinis) was associated with gastric cancer cell migration and invasion, but the mechanisms were not well understood. Herein, we found that M. hyorhinis activated phosphoinositide 3-kinase (PI3K)-AKT signaling axis in gastric cancer cell lines. Epidermal growth factor receptor (EGFR) was upstream of PI3K-AKT signaling in the context of M. hyorhinis infection, because phosphorylation of AKT Serine 473 was almost completely attenuated by the EGFR inhibitor AG1478 or by EGFR knockdown. Phosphorylation of AKT S473 induced by M. hyorhinis infection was also abolished by PI3K inhibitor wortmannin. Furthermore, we found that p37, a membrane protein of M. hyorhinis, could also promote M. hyorhinis-induced PI3K-AKT signaling activation and cell migration. In addition, pre-treatment with AG1478 or wortmannin significantly inhibited cell migration induced by M. hyorhinis infection or p37 treatment. In conclusion, EGFR-PI3K-AKT signaling plays an important role in M. hyorhinis-promoted cell migration in gastric cancer cells, thus providing a clue to the pathogenesis of M. hyorhinis in gastric cancer.

Detection of mycoplasma infection in circulating tumor cells in patients with hepatocellular carcinoma

Many studies have shown that persistent infections of bacteria promote carcinogenesis and metastasis. Infectious agents and their products can modulate cancer progression through the induction of host inflammatory and immune responses. The presence of circulating tumor cells (CTCs) is considered as an important indicator in the metastatic cascade. We unintentionally produced a monoclonal antibody (MAb) CA27 against the mycoplasmal p37 protein in mycoplasma-infected cancer cells during the searching process of novel surface markers of CTCs. Mycoplasma-infected cells were enriched by CA27-conjugated magnetic beads in the peripheral blood mononuclear cells in patients with hepatocellular carcinoma (HCC) and analyzed by confocal microscopy with anti-CD45 and CA27 antibodies. CD45-negative and CA27-positive cells were readily detected in three out of seven patients (range 12-30/8.5 ml blood), indicating that they are mycoplasma-infected circulating epithelial cells. CA27-positive cells had larger size than CD45-positive hematological lineage cells, high nuclear to cytoplasmic ratios and irregular nuclear morphology, which identified them as CTCs. The results show for the first time the existence of mycoplasma-infected CTCs in patients with HCC and suggest a possible correlation between mycoplasma infection and the development of cancer metastasis.

Structure of a eukaryotic thiaminase I

Thiaminases, enzymes that cleave vitamin B1, are sporadically distributed among prokaryotes and eukaryotes. Thiaminase I enzymes catalyze the elimination of the thiazole ring moiety from thiamin through substitution of the methylene group with a nitrogenous base or sulfhydryl compound. In eukaryotic organisms, these enzymes are reported to have much higher molecular weights than their bacterial counterparts. A thiaminase I of the single-celled amoeboflagellate Naegleria gruberi is the only eukaryotic thiaminase I to have been cloned, sequenced, and expressed. Here, we present the crystal structure of N. gruberi thiaminase I to a resolution of 2.8 Å, solved by isomorphous replacement and pseudo-two-wavelength multiwavelength anomalous diffraction and refined to an R factor of 0.231 (Rfree, 0.265). This structure was used to solve the structure of the enzyme in complex with 3-deazathiamin, a noncleavable thiamin analog and enzyme inhibitor (2.7 Å; R, 0.233; Rfree, 0.267). These structures define the mode of thiamin binding to this class of thiaminases and indicate the involvement of Asp272 as the catalytic base. This enzyme is able to use thiamin as a substrate and is active with amines such as aniline and veratrylamine as well as sulfhydryl compounds such as l-cysteine and β-mercaptoethanol as cosubstrates. Despite significant differences in polypeptide sequence and length, we have shown that the N. gruberi thiaminase I is homologous in structure and activity to a previously characterized bacterial thiaminase I.

Optimized protocol for multiplex nested polymerase chain reaction to detect and differentiate Haemophilus parasuis, Streptococcus suis, and Mycoplasma hyorhinis in formalin-fixed, paraffin-embedded tissues from pigs with polyserositis

An optimized protocol was developed for the simultaneous detection and differentiation of Haemophilus parasuis, Streptococcus suis, and Mycoplasma hyorhinis in formalin-fixed, paraffin-embedded (FFPE) tissues with multiplex nested polymerase chain reaction (PCR). This method also determines the prevalence of these bacteria in pigs with polyserositis. DNA extraction with a combination of a commercial reagent and proteinase K resulted in more frequent detection of the pathogens than DNA extraction with proteinase K alone. Among FFPE tissue samples from 312 cases of polyserositis in which at least 1 bacterial species was detected, multiplex nested PCR detected H. parasuis in 239 (77%), S. suis in 124 (40%), and M. hyorhinis in 40 (13%). The disease was caused by a single pathogen in 224 (72%) of the cases and multiple pathogens in 88 (28%). Among the pigs positive for H. parasuis, S. suis, and M. hyorhinis by multiplex nested PCR, the pathogen was isolated from only 11%, 35%, and 28%, respectively. Therefore, the PCR protocol developed in this study is a useful diagnostic method when samples are negative after isolation methods and even for samples in which only 1 pathogen was isolated.

Proteomics characterization of cytoplasmic and lipid-associated membrane proteins of human pathogen Mycoplasma fermentans M64

Mycoplasma fermentans is a potent human pathogen which has been implicated in several diseases. Notably, its lipid-associated membrane proteins (LAMPs) play a role in immunomodulation and development of infection-associated inflammatory diseases. However, the systematic protein identification of pathogenic M. fermentans has not been reported. From our recent sequencing results of M. fermentans M64 isolated from human respiratory tract, its genome is around 1.1 Mb and encodes 1050 predicted protein-coding genes. In the present study, soluble proteome of M. fermentans was resolved and analyzed using two-dimensional gel electrophoresis. In addition, Triton X-114 extraction was carried out to enrich amphiphilic proteins including putative lipoproteins and membrane proteins. Subsequent mass spectrometric analyses of these proteins had identified a total of 181 M. fermentans ORFs. Further bioinformatics analysis of these ORFs encoding proteins with known or so far unknown orthologues among bacteria revealed that a total of 131 proteins are homologous to known proteins, 11 proteins are conserved hypothetical proteins, and the remaining 39 proteins are likely M. fermentans-specific proteins. Moreover, Triton X-114-enriched fraction was shown to activate NF-kB activity of raw264.7 macrophage and a total of 21 lipoproteins with predicted signal peptide were identified therefrom. Together, our work provides the first proteome reference map of M. fermentans as well as several putative virulence-associated proteins as diagnostic markers or vaccine candidates for further functional study of this human pathogen.

Insights into Mycoplasma genitalium metabolism revealed by the structure of MG289, an extracytoplasmic thiamine binding lipoprotein

Mycoplasma genitalium is one of the smallest organisms capable of self-replication and its sequence is considered a starting point for understanding the minimal genome required for life. MG289, a putative phosphonate substrate binding protein, is considered to be one of these essential genes. The crystal structure of MG289 has been solved at 1.95 Å resolution. The structurally identified thiamine binding region reveals possible mechanisms for ligand promiscuity. MG289 was determined to be an extracytoplasmic thiamine binding lipoprotein. Computational analysis, size exclusion chromatography, and small angle X-ray scattering indicates that MG289 homodimerizes in a concentration-dependant manner. Comparisons to the thiamine pyrophosphate binding homolog Cypl reveal insights into the metabolic differences between mycoplasmal species including identifying possible kinases for cofactor phosphorylation and describing the mechanism of thiamine transport into the cell. These results provide a baseline to build our understanding of the minimal metabolic requirements of a living organism.

Transcriptional response of Mycoplasma genitalium to osmotic stress

Mycoplasma genitalium is the causative agent of non-gonococcal, chlamydia-negative urethritis in men and has been linked to reproductive tract disease syndromes in women. As with other mycoplasmas, M. genitalium lacks many regulatory genes because of its streamlined genome and total dependence on a parasitic existence. Therefore, it is important to understand how gene regulation occurs in M. genitalium, particularly in response to environmental signals likely to be encountered in vivo. In this study, we developed an oligonucleotide-based microarray to investigate transcriptional changes in M. genitalium following osmotic shock. Using a physiologically relevant osmolarity condition (0.3 M sodium chloride), we identified 39 upregulated and 72 downregulated genes. Of the upregulated genes, 21 were of unknown function and 15 encoded membrane-associated proteins. The majority of downregulated genes encoded enzymes involved in energy metabolism and components of the protein translation process. These data provide insights into the in vivo response of M. genitalium to hyperosmolarity conditions and identify candidate genes that may contribute to mycoplasma survival in the urogenital tract.

Biochemical characterization of ThiT from Lactococcus lactis: a thiamin transporter with picomolar substrate binding affinity

The putative thiamin transporter ThiT from Lactococcus lactis was overproduced in the membrane of lactococcal cells. In vivo transport assays using radiolabeled thiamin demonstrated that ThiT indeed was involved in thiamin transport. The protein was solubilized from the membranes and purified in detergent solution. Size exclusion chromatography coupled to static light scattering, refractive index, and UV absorbance measurements (SEC-MALLS) showed that ThiT is a monomer of 22.7 kDa in detergent solution. When the cells overexpressing ThiT had been cultivated in complex growth medium, all binding sites of the purified protein were occupied with substrate, which had copurified with the protein. MALDI-TOF mass spectrometry analysis confirmed that the copurified substance was thiamin. Substrate-depleted ThiT was obtained by expressing the protein in cells that were cultivated in chemically defined growth medium without thiamin. The intrinsic tryptophan fluorescence of substrate-depleted ThiT was strongly quenched upon thiamin binding. The quenching of the fluorescence was used to determine dissociation constants for thiamin and related compounds. ThiT had an unusually high affinity for thiamin (K(D) = 122 +/- 13 pM) and bound the substrate with a 1:1 (protein:ligand) stoichiometry. TPP, TMP, and pyrithiamin bound to ThiT with nanomolar affinity. A multiple sequence alignment of ThiT homologues revealed that well-conserved residues were clustered in a tryptophan-rich stretch comprising the loop between the predicted membrane spanning segments 5 and 6. Mutational analysis of the conserved residues in this region combined with binding assays of thiamin and related compounds was used to build a model of the high-affinity binding site. The model was compared with thiamin binding sites of other proteins and interpreted in terms of the transport mechanism.

Persistent exposure to Mycoplasma induces malignant transformation of human prostate cells

Recent epidemiologic, genetic, and molecular studies suggest infection and inflammation initiate certain cancers, including those of the prostate. The American Cancer Society, estimates that approximately 20% of all worldwide cancers are caused by infection. Mycoplasma, a genus of bacteria that lack a cell wall, are among the few prokaryotes that can grow in close relationship with mammalian cells, often without any apparent pathology, for extended periods of time. In this study, the capacity of Mycoplasma genitalium, a prevalent sexually transmitted infection, and Mycoplasma hyorhinis, a mycoplasma found at unusually high frequency among patients with AIDS, to induce a malignant phenotype in benign human prostate cells (BPH-1) was evaluated using a series of in vitro and in vivo assays. After 19 weeks of culture, infected BPH-1 cells achieved anchorage-independent growth and increased migration and invasion. Malignant transformation of infected BPH-1 cells was confirmed by the formation of xenograft tumors in athymic mice. Associated with these changes was an increase in karyotypic entropy, evident by the accumulation of chromosomal aberrations and polysomy. This is the first report describing the capacity of M. genitalium or M. hyorhinis infection to lead to the malignant transformation of benign human epithelial cells and may serve as a model to further study the relationship between prostatitis and prostatic carcinogenesis.

Cloning, expression, purification, crystallization and preliminary X-ray analysis of Mycoplasma genitalium protein MG289

Mycoplasma genitalium is a human pathogen that is associated with nongonococcal urethritis in men and cervicitis in women. The cloning, expression, purification and crystallization of the protein MG289 from M. genitalium strain G37 are reported here. Crystals of MG289 diffracted X-rays to 2.8 A resolution. The crystals belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 49.7, b = 90.9, c = 176.1 A. The diffraction data after processing had an overall R(merge) of 8.7%. The crystal structure of Cypl, the ortholog of MG289 from M. hyorhinis, has recently been determined, providing a reasonable phasing model; molecular replacement is currently under way.