Triton X-114 phase fractionation of an integral membrane surface protein mediating monoclonal antibody killing of Mycoplasma hyorhinis

Characterization of the role in adherence of Mycoplasma hyorhinis variable lipoproteins containing different repeat unit copy numbers

Mycoplasma hyorhinis (M. hyorhinis) is an important pathogen of pigs. In previous studies, the variable lipoprotein (Vlp) family has been shown to play a role in mediating M. hyorhinis cytoadhesion. Herein, we performed several experiments to study the function of each Vlp family member in detail, especially examining the cytoadhesion functional domain and how the repeat unit copy number impacts on function. Recombinant proteins rVlpII, composed of region II from all seven Vlp members; rVlpIII, composed of repeat peptides from region III of all of Vlp members; as well as a series of recombinant rVlp proteins for each member containing different repeat unit copy numbers were constructed. All of the proteins were expressed in Escherichia coli and purified by affinity chromatography. The recombinant proteins, as well as seven keyhole limpet hemocyanin-conjugated Vlp peptides containing two copies of the repeat unit, were analyzed for their adherence to swine tracheal epithelial cells using a microtiter plate adherence assay. Both rVlpII and rVlpIII proteins were able to bind to cell membrane proteins. Among the repeat unit peptides, only PepVlpB and PepVlpG were able to bind to cell membrane proteins. All of the Vlp members had cytoadhesion capability. The adhesion abilities of the proteins containing 0 or 3 copies of the repeat unit were stronger than those of the proteins containing 12 copies. For rVlpA, rVlpB, rVlpD, rVlpF and rVlpG, the proteins containing no copies bound stronger than the proteins containing 3 copies. In contrast, the adherence of rVlpC3 was stronger than that of rVlpC0. There was no significant difference between the adherence of rVlpE3 and that of rVlpE0. Our results suggest that the major cytoadhesion sites of Vlps are mainly contained in region II, the function of which would be blocked by region III when region III is longer.

Proteomic approach for identification of immunogenic proteins of Mycoplasma mycoides subsp. capri

In this study, an immunoproteomic approach was used to identify immunodominant proteins from Mycoplasma mycoides subsp. capri isolates. Membrane proteins, extracted through TX-114 phase partitioning, were separated using mono- and two-dimensional electrophoresis and detected by Western blotting with pooled sera from naturally infected goats. A total of 27 immunoreactive spots, corresponding to 13 different proteins, were identified using nanoLC-ESI-MSMS. Function annotation revealed that most of these proteins were metabolic enzymes involved in carbohydrate and energy metabolism. The immunogenic proteins identified in this study: pyruvate dehydrogenase, dihydrolipoamide acetyltransferase, dihydrolipoyl dehydrogenase, phosphate acetyltransferase, phosphopyruvate hydratase, adenine phopshoribosyltransferase, transketolase, translation elongation factor G, translation elongation factor Ts, FMN-dependent NADH-azoreductase, peptide methionine sulfoxide reductase, inorganic diphosphatase and trigger factor may be used as biomarkers for the serological diagnosis of contagious agalactia caused by M. mycoides subsp. capri.

Resistance of Spiroplasma citri Lines to the Virus SVTS2 Is Associated with Integration of Viral DNA Sequences into Host Chromosomal and Extrachromosomal DNA

Spiroplasmavirus SVTS2, isolated from Spiroplasma melliferum TS2, produces plaques when inoculated onto lawns of Spiroplasma citri M200H, a derivative of the type strain Maroc R8A2. S. citri strains MR2 and MR3, originally selected as colonies growing within plaques on a lawn of M200H inoculated with SVTS2, were resistant to SVTS2. Genomic DNA fingerprints and electrophoretic protein profiles of M200H, MR2, and MR3 were similar, but three proteins present in M200H were missing or significantly reduced in both resistant lines. None of these three polypeptides reacted with antiserum against S. citri membrane proteins, indicating that they probably are not surface-located virus receptors. Electroporation with SVTS2 DNA produced 1.5 x 10(sup5) transfectants per (mu)g of DNA in M200H but none in MR2 or MR3, suggesting that resistance may result from inhibition of viral replication. The digestion patterns of the extrachromosomal double-stranded (ds) DNA of these lines were similar. Three TaqI fragments of MR2 extrachromosomal DNA that were not present in M200H extrachromosomal DNA hybridized strongly to an SVTS2 probe, and two of these fragments plus an additional one hybridized with the MR3 extrachromosomal DNA, indicating that a fragment of SVTS2 DNA was present in the extrachromosomal ds DNA of MR2 and MR3 but not of M200H. When the restricted genomes of all three lines were probed with SVTS2 DNA, strong hybridization to two EcoRI fragments of chromosomal MR2 and MR3 DNA but not M200H DNA indicated that SVTS2 DNA had integrated into the genomes of MR2 and MR3 but not of M200H. When MR3 extrachromosomal ds DNA containing a 2.1-kb SVTS2 DNA fragment was transfected into M200H, the transformed spiroplasmas were resistant to SVTS2. These results suggest that SVTS2 DNA fragments, possibly integrated into the chromosomal or extrachromosomal DNA of a previously susceptible spiroplasma, may function as viral incompatibility elements, providing resistance to superinfection by SVTS2.

Identification of appressorial and mycelial cell wall proteins and a survey of the membrane proteome of Phytophthora infestans

Proteins embedded in the cell wall and plasma membrane of filamentous oomycetes and fungi provide a means by which these organisms can interact with their local environment. However, cell wall and membrane proteins have often proved difficult to isolate using conventional proteomic techniques. Here we have used liquid chromatography tandem mass spectrometry (LC-MS/MS) to facilitate rapid and sensitive quantification of the cell wall proteome. We report the use of LC-MS/MS to identify differentially regulated proteins from the cell walls of three different lifecycle stages of the oomycete plant pathogen Phytophthora infestans: non-sporulating vegetative mycelium, sporulating mycelium, and germinating cysts with appressoria. We have also used quantitative real-time RT-PCR to confirm that the transcripts corresponding to some of these proteins, namely those identified in cell walls of germinating cysts with appressoria, accumulate differentially throughout the lifecycle. These proteins may, therefore, be important for pre-infective development and early pathogenicity. Up to 31 covalently and non-covalently bound cell wall-associated proteins were identified. All of the proteins identified in germinating cysts with appressoria, and several of those from mycelial fractions, were classified as putative effector or pathogen-associated molecular pattern (PAMP) molecules, including members of the CBEL family, the elicitin family, the crinkler (CRN) family and two transglutaminases. Thus, the cell wall of P. infestans may represent an important reservoir for surface-presented, apoplastic effectors or defence activation molecules. Proteins predicted to be cell surface proteins included IPI-B like proteins, mucins, cell wall-associated enzymes and annexin family members. Additionally we identified up to 27 membrane-associated proteins from Triton X-114 phase partitioned mycelial membrane preparations, producing the first inventory of oomycete membrane-associated proteins. Four of these proteins are small Rab-type G-proteins and several are associated with secretion.

Characterization of a unique ADP-ribosyltransferase of Mycoplasma penetrans

Mycoplasma penetrans is a urogenital tract pathogen implicated in the deterioration of the immune system in human immunodeficiency virus-infected AIDS patients. Here, we describe a 78-kDa protein from M. penetrans, designated MYPE9110, that exhibits sequence similarity to known ADP-ribosyltransferases (ADPRTs) such as Bordetella pertussis pertussis toxin and Mycoplasma pneumoniae community-acquired respiratory distress syndrome toxin. MYPE9110 possesses key amino acid residues found in all ADPRTs that are essential for ADPRT activity. Several mammalian cell proteins are ADP-ribosylated by MYPE9110, and the full-length recombinant protein exhibits a strong auto-ADP-ribosylating activity. In the absence of target proteins, MYPE9110 demonstrates a NAD-glycohydrolase activity by hydrolyzing NAD. Furthermore, this toxin elicits cytopathology in HeLa cells by inducing cytoplasmic vacuolization in the presence of ammonium chloride. The deletion of the C-terminal region of MYPE9110 significantly diminishes its binding to host cells while still exhibiting an ADPRT activity, suggesting that MYPE9110 is a member of the family of A-B ADPRT toxins.

Mycoplasma genitalium-encoded MG309 activates NF-kappaB via Toll-like receptors 2 and 6 to elicit proinflammatory cytokine secretion from human genital epithelial cells

Mycoplasma genitalium has been implicated in several important reproductive tract syndromes in women, including pelvic inflammatory disease, cervicitis, and tubal factor infertility. The mechanisms of immune activation are unclear, and we sought to determine whether M. genitalium was capable of activating innate immune responses through ligation of highly expressed Toll-like receptors (TLR) of the genital tract. Using HEK293 cells expressing specific human TLR, viable M. genitalium and the recombinant C-terminal portion of the immunogenic protein MG309 (rMG309c) were shown to activate NF-kappaB via TLR2/6. These data provided a putative mechanism for activation of the innate response in genital tissues. Genital epithelial cells (EC) are the first responders to sexually transmitted pathogens and express high levels of TLR2 and -6. Following exposure to purified rMG309c, vaginal and ecto- and endocervical EC secreted proinflammatory cytokines, including interleukin-6 (IL-6) and IL-8. Vaginal EC were less responsive than cervical EC. The capacity of rMG309c to bind TLR2/6 and elicit inflammation was sensitive to proteinase K digestion and independent of traditional N-terminal lipoylation. Furthermore, the immunostimulatory capacity of rMG309c was localized specifically to a 91-amino-acid subfragment of the recombinant protein, suggesting that TLR activation is likely amino acid based. Together, these data indicated that human vaginal and cervical EC are immunologically responsive to M. genitalium and to purified rMG309c via highly expressed TLR of the genital tract. These findings provide valuable insights into the mechanisms for activation of acute-phase inflammatory responses and suggest that M. genitalium colonization of reproductive tract tissues may result in inflammatory sequelae.

The surface-exposed carboxyl region of Mycoplasma pneumoniae elongation factor Tu interacts with fibronectin

Mycoplasma pneumoniae is a bacterial pathogen of the human respiratory tract that causes a wide range of airway diseases as well as extrapulmonary symptoms. It possesses a distinct, differentiated terminal structure, termed the attachment organelle, that mediates adherence to the host respiratory epithelium. Previously, we reported that surface-associated M. pneumoniae elongation factor Tu (EF-Tu, also called MPN665) serves as a fibronectin (Fn)-binding protein, facilitating interactions between mycoplasmas and extracellular matrix. In the present study, we determined that binding of M. pneumoniae EF-Tu to Fn is primarily mediated by the EF-Tu carboxyl region. A 179-amino-acid region spanning the carboxyl terminus (designated EC; amino acids 192 to 394) binds Fn in a dose-dependent manner. Further analysis of carboxyl constructs (ED3 and ED4) and their deletion truncations (ED3.1, ED3.2, and ED4.1) revealed that the carboxyl region possessed two distinct sites with different Fn-binding efficiencies. Immunogold electron microscopy using antibodies raised against recombinant ED3 and ED4 demonstrated the surface accessibility of the EF-Tu carboxyl region. Competitive binding assays using intact radiolabeled mycoplasmas and purified recombinant ED3 and ED4 proteins, along with antibody blocking assays, reinforced the role of the surface-exposed EF-Tu carboxyl region in Fn binding. Alkali and high-salt treatment of mycoplasma membranes and Triton X-114-partitioned mycoplasma fractions confirmed the stable association of EF-Tu within the mycoplasma membrane. These observations highlight the unique, multifaceted, and unpredictable role of the classically defined cytoplasmic protein EF-Tu relative to cellular function, compartmentalization, and topography.

Improved sensitivity and specificity of enzyme immunoassays with P1-adhesin enriched antigen to detect acute Mycoplasma pneumoniae infection

An in-house P1-enriched (168-kDA protein) Mycoplasma pneumoniae antigen preparation was compared in IgG, IgA and IgM enzyme immunoassays (EIAs) to the respective EIAs employing crude antigen lysate, antigen prepared by Triton X-114 partition and two commercial antigens, one of which was an ether-extracted antigen and the other a P1-enriched antigen. In addition, three commercial kits from Sanofi Pasteur, Novum Diagnostica and Savyon Diagnostics were also assessed for comparison. Diagnostic sensitivity was studied with paired samples from adults (n=37) with acute respiratory illness interpreted as acute, recent or past infection to M. pneumoniae on the basis of the results of complement fixation test (CFT). If the consensus of at least two methods is taken as the true positive for acute infection, the diagnostic sensitivities of combined IgG and IgM EIAs were 100% for the Platelia(R), Sero MP and in-house EIAs whereas for the Novum EIAs and CFT- 97% and 74%, respectively. Moreover, the sensitivity of the P1-enriched antigen was proven superior on the basis of systematically highest OD(405 nm) ratios between convalescent and acute serum samples. Analytical specificity was studied by screening serum samples from 92 Finnish blood donors and 111 serum samples from cord blood. Diagnostic specificity was studied in a blind testing of 30 paired serum samples from infants with pneumonia of variable etiology. No single misinterpretation of acute infection from the group of samples with other respiratory diseases did occur. The present study confirmed and extended the earlier observations of the usefulness of P1-enriched antigen for reliable serologic diagnosis of acute M. pneumoniae infection.

Towards a two-dimensional proteome map of Mycoplasma pneumoniae

A Proteome map of the bacterium Mycoplasma pneumoniae was constructed using two-dimensional (2-D) gel electrophoresis in combination with mass spectrometry (MS). M. pneumoniae is a human pathogen with a known genome sequence of 816 kbp coding for only 688 open reading frames, and is therefore an ideal model system to explore the scope and limits of the current technology. The soluble protein content of this bacterium grown under standard laboratory conditions was separated by 1-D or 2-D gel electrophoresis applying various pH gradients, different acrylamide concentrations and buffer systems. Proteins were identified using liquid chromatography-electrospray ionization ion trap and matrix-assisted laser desorption/ionization-MS. Mass spectrometric protein identification was supported and controlled using N-terminal sequencing and immunological methods. So far, proteins from about 350 spots were characterized with MS by determining the molecular weights and partial sequences of their tryptic peptides. Comparing these experimental data with the DNA sequence-derived predictions it was possible to assign these 350 proteins to 224 genes. The importance of proteomics for genome analysis was shown by the identification of four proteins, not annotated in the original publication. Although the proteome map is still incomplete, it is already a useful reference for comparative analyses of M. pneumoniae cells grown under modified conditions.

The subunit b of the F0F1-type ATPase of the bacterium Mycoplasma pneumoniae is a lipoprotein

The DNA sequence analysis of the F0F1-ATPase operon of the bacterium Mycoplasma pneumoniae predicted that the subunit b, encoded by the gene atpF, is a lipoprotein of the murein lipoprotein type of Escherichia coli. Here we experimentally verify this prediction by metabolic labeling of subunit b with [14C]palmitic acid and by in vivo interfering with the processing of the prolipoprotein form of subunit b by the antibiotic globomycin, a specific inhibitor of the signal peptidase II. Our results suggest that the subunit b of the F0F1-ATPase of M. pneumoniae is anchored at the cytoplasmic membrane by an N-terminal lipid modification in addition to its transmembrane domain. The lipoprotein nature of subunit b and its proposed membrane topology seems to be characteristic for mycoplasmas, since among all sequenced bacterial atpF genes, only those from Mycoplasma gallisepticum and Mycoplasma genitalium code for a conserved lipoprotein consensus sequence.

Antigen heterogeneity among Mycoplasma mycoides subsp. mycoides SC isolates: discrimination of major surface proteins

The protein and antigen profiles of 60 isolates, strains and the type strain PG1 of Mycoplasma mycoides subsp. mycoides s.c. were compared by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblot analysis. Analysis using contagious bovine pleuropneumonia antisera and hyperimmune rabbit sera against several representative strains revealed some differences in protein profiles and variability in antigens among strains from different geographic regions. The most common antigenic bands had the molecular masses of 110, 95, 80, 69, 62, 60, 48, 44, 39 and 38 kDa. There were differences among European strains, where a larger group coming from Italy lacked the p98 antigen, thus, with one exception, distinguishing the Italian strains from Portuguese, French and Spanish strains. African, Australian and PG1 strains showed heterogenic profiles, with quantitative differences and in a few strains some antigenic bands were absent. The group constituting African, Australian and PG1 strains was characterised by the presence of 71.5/70 kDa antigens, which were not detected in European strains. Mycoplasma mycoides subsp. mycoides s.c. membrane proteins were characterised by Triton X-114 partitioning and p110, p98, p95, p62/60 and p48 were identified as immunogenic antigens. The simultaneous presence of these five antigens was common to all the sera examined and, therefore, indicates the diagnostic potential of immunoblotting. Most immunodominant antigens are surface-exposed proteins as determined by the trypsin treatment.

Characterization of membrane surface proteins of Mycoplasma agalactiae during natural infection

We have analyzed antigenic variation of seven M. agalactiae wild strains using different sera from naturally infected sheep. Only 30 day sera recognized all surface proteins and inhibited the growth of mycoplasmas. Furthermore, we have observed that two strongly immunogenic proteins: 55 and 35 kDa were digested using 500 micrograms/ml of trypsin. These two bands are immunoprecipitated together with four other proteins but only the 35 kDa protein is recognized by eluted antibodies.

Monoclonal antibody E8-18 identifies an integral membrane surface protein unique to Mycoplasma capricolum subsp. capripneumoniae

Monoclonal antibody (MAb) E8-18 reacted with four isolates of Mycoplasma capricolum subsp. capripneumoniae in Western blots identifying an epitope on a 24 kDa antigen (p24). MAb E8-18 did not react with 11 isolates belonging to four other Mycoplasma species or subspecies closely related to M. capricolum subsp. capripneumoniae. A combination of trypsin treatment of intact organisms and detergent-phase partitioning revealed p24 to be an integral M. capricolum subsp. capripneumoniae surface membrane protein.

Elongated versions of Vlp surface lipoproteins protect Mycoplasma hyorhinis escape variants from growth-inhibiting host antibodies

Variation in Vlp surface proteins of Mycoplasma hyorhinis was evaluated in terms of its role in determining susceptibility of organisms to growth inhibition by host antibodies (Abs). High-frequency switching of Vlp surface lipoproteins has been studied in isogenic lineages of M. hyorhinis SK76. In these lineages, the products of three genes, vlpA, vlpB, and vlpC, are subject to phase and size variation in vitro, which occur through distinct mutator elements that independently govern the expression of each vlp gene (promoter mutations) or the size of the vlp gene product (by intragenic expansion or contraction of a 3' region containing tandem repeats). Isogenic clonal variants of M. hyorhinis SK76 expressing distinct profiles of Vlp products were assessed for their susceptibility to complement-independent growth inhibition by serum Abs of swine experimentally infected with the arthritigenic SK76 strain. Invariably, variants expressing longer versions of VlpA, VlpB, or VlpC (each expressed individually) were completely resistant to host immune serum Abs, whereas variants expressing shorter allelic versions of each Vlp were susceptible. The target of growth-inhibiting Abs was not the Vlp products, since removal of anti-Vlp Abs had no effect on the inhibitory activity of the host immune serum on susceptible variants. Escape variant populations derived by propagating susceptible variants in an immune (versus control) host serum revealed a strong selection for the long-Vlp phenotype, irrespective of the identity of the Vlp expressed. Apparent mutational pathways of acquiring the protective phenotype included mutational switches to express long vlp genes that had been transcriptionally silent or switches to elongate expressed vlp genes. These results suggest that a major function of the Vlp system is to shield the wall-less mycoplasma surface from host Abs capable of binding vital (and as-yet-unidentified) surface antigens of this organism.

Monoclonal antibodies to surface-exposes proteins of Mycoplasma mycoides subsp. mycoides (small-colony strain), which causes contagious bovine pleuropneumonia

Outbreaks of bovine pleuropneumonia caused by small-colony strains of Mycoplasma mycoides subsp. mycoides occur in Africa, and vaccination is used for control. Since protein subunits are needed to improve multivalent vaccines, monoclonal antibodies (MAbs) were made to facilitate protein identification and isolation. Eleven immunoglobulin M MAbs derived from mouse spleen donors immunized with disrupted whole organisms bound periodate-sensitive epitopes on externally exposed polysaccharide. Seven of these MAbs caused in vitro growth inhibition of M. mycoides subsp. mycoides; however, reaction with carbohydrate epitopes prevented their use in identifying proteins. Ten additional MAbs from mouse spleen donors immunized with Triton X-114-phase integral membrane proteins reacted with periodate-insensitive, proteinase K-sensitive epitopes. These MAbs were classified into three groups based on immunoblots of Triton X-114-phase proteins. One group reacted with 96-, 16-, and 15-kDa proteins. Another group reacted with 26-, 21-, and 16-kDa proteins, while a third group reacted only with 26- and 21-kDa proteins. One MAb from each group reacted with trypsinsensitive epitopes on live organisms, yet none caused in vitro growth inhibition. Representative MAbs reacted with all small-colony strains in immunoblots and did not react with large colony strains. However, these MAbs were not specific for small-colony strains, as proteins from two other M. mycoides cluster organisms were identified. Nevertheless, MAbs to surface-exposed epitopes on integral membrane proteins will be useful for isolation of these proteins for immunization, since one or more might induce growth-inhibiting antibodies or other protective responses.

Comparison of Mycoplasma agalactiae isolates by pulsed field gel electrophoresis, SDS-PAGE and immunoblotting

We have analyzed 81 isolates of Mycoplasma agalactiae from four different regions of Italy between 1990 and 1995 in order to identify antigenic differences through SDS-PAGE and Western blotting and chromosomal DNA restriction endonuclease cleavage pattern differences. Antigenic variability in M. agalactiae isolates was investigated analyzing hydrophobic membrane protein fractions by immunoblotting using pooled sheep antiserum from naturally infected sheep. Large restriction fragments obtained cleaving genomic DNAs with SmaI, NruI, SalI, XhoI, BssHII and KpnI were analyzed by pulsed field gel electrophoresis. Genetic analysis indicates that isolates are all similar without intraspecific differences. This homogeneity was confirmed by immunoblotting: 80 and 50 kDa antigens are present in all strains analyzed.

Isotype-specific antibody responses to acute Mycoplasma pneumoniae infection

BACKGROUND

Mycoplasma pneumoniae-induced respiratory infections affect millions of patients and have been implicated in exacerbation of bronchial asthma. IgE may be involved in such exacerbations. While specific IgG and IgM responses to Mycoplasma pneumoniae are well described, the response of other isotypes is less known.

PURPOSE

To determine whether specific IgE and what subclasses of IgG are formed in response to Mycoplasma pneumoniae infection.

METHODS

We studied 20 patients with acute Mycoplasma pneumoniae infection, in whom the diagnosis was confirmed by a 16-fold increase in complement fixation titer between acute and convalescent serum samples. We developed an enzyme-linked immunosorbent assay (ELISA) for the determination of IgG, IgA, and IgM antibodies specific for Mycoplasma pneumoniae protein antigens. We used Western blotting to confirm the results of the ELISA and to detect Mycoplasma-specific IgG subclasses and IgE.

RESULTS

Changes in Mycoplasma pneumoniae-specific IgG, IgA, and IgM were significant. Western blots of Mycoplasma pneumoniae antigens in 13 convalescent sera showed specific IgG in all, IgM in 11, IgA in 6, and IgE in 10. The IgG response consisted mainly of IgG1 and IgG3, and to a lesser degree of IgG2 and IgG4.

CONCLUSIONS

We conclude that Mycoplasma pneumoniae infection is associated with a significant specific IgA and IgE response, in addition to the well-known responses of IgG and IgM. As IgE is involved in allergic reactions, the production of Mycoplasma pneumoniae-specific IgE may have a role in exacerbation of bronchial asthma.

Purification of hydrophobic integral membrane proteins from Mycoplasma hyopneumoniae by reversed-phase high-performance liquid chromatography

A general and practical approach for isolating, fractionating and purifying large quantities of outer membrane hydrophobic proteins is described as applied to membrane proteins of Mycoplasma hyopneumoniae. Outer membrane proteins were extracted with Triton X-114 detergent and were precipitated from the detergent phase with 90% ethanol. Precipitated proteins were dissolved in 65% formic acid and separated by RP-HPLC using a formic acid-acetonitrile gradient. A M(r) 48 000 protein was obtained in high yield and at greater than 90% purity by optimisation of parameters for RP-HPLC. The combination of Triton X-114 extraction followed by high resolution RP-HPLC is a novel and rapid procedure for the isolation and purification of hydrophobic proteins. Proteins purified by this approach were suitable for subsequent characterisation by direct sequencing of the amino terminus as well as generation of peptides by digestion with cyanogen bromide.

Antigen heterogeneity among isolates of Mycoplasma bovis is generated by high-frequency variation of diverse membrane surface proteins

The protein and antigen profiles of 11 isolates of Mycoplasma bovis were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis of whole organisms. The isolates examined included the type strain PG45 and 10 other filter-cloned strains or purified isolates both from animals without clinical signs and from clinical cases of bovine mastitis, arthritis, or pneumonia. While the overall protein patterns visualized by silver staining were very similar, marked differences in the antigen banding profiles were detected by rabbit antiserum prepared against whole organisms from one of the strains analyzed. This antigenic heterogeneity was shown to be independent of the geographical origin, the type of clinical disease, and the site of isolation and was also observed among serial isolates from a single animal. Antigen profiles were further monitored throughout sequentially subcloned populations of the PG45 strain. This clonal analysis revealed a high-frequency variation in the expression levels of several prominent antigens. All of these variable antigens were defined by detergent-phase fractionation with Triton X-114 as amphiphilic integral membrane proteins. A subset of different-sized membrane proteins was identified by a monoclonal antibody raised against a PG45 subclone expressing a 63- and a 46-kDa variant antigen within that set. The selective susceptibility of these proteins to trypsin treatment of intact organisms and their ability to bind the monoclonal antibody in colony immunoblots demonstrated that they were exposed on the cell surface. In addition, their preferential recognition by serum antibodies from individual cattle with naturally induced M. bovis mastitis or arthritis confirmed that they were major immunogens of this organism. These studies establish that the apparent antigenic heterogeneity among M. bovis isolates reported here does not represent stable phenotypic strain differences generated from accumulated mutational events but reflects distinct expression patterns of diverse, highly variable membrane surface proteins.

Identification and characterization of hitherto unknown Mycoplasma pneumoniae proteins

Eleven hitherto unknown Mycoplasma pneumoniae proteins were identified and characterized with respect to their size and subcellular location. This was carried out through the construction of in vitro gene fusions between a modified mouse dehydrofolate reductase (dhfr) gene and selected regions (cosmid clones) of the M. pneumoniae genome and expressing them in Escherichia coli. Positive clones were identified using antibodies against specific fractions of M. pneumoniae. The deduced protein sequences of 11 out of 30 clones did not show significant homologies to known proteins in protein data-bank searches. Monospecific antibodies against these 11 fusion proteins were used to determine the size and cellular location of the corresponding M. pneumoniae proteins by immunoscreening Western blots of SDS-acrylamide gels from M. pneumoniae cell extracts.

Processing and surface presentation of the Mycoplasma hyorhinis variant lipoprotein VlpC

The variant surface lipoprotein VlpC of Mycoplasma hyorhinis was shown to be processed by cleavage of a characteristic prokaryotic prolipoprotein signal peptide. In addition, a vlpC::phoA fusion protein expressed and translocated in Escherichia coli was recognized by surface-binding monoclonal antibodies, which identified the characteristic region II of Vlps, containing divergent external sequences proximal to the membrane, as an exposed portion of these surface proteins subject to immune recognition and selection.

Phase separation of biomolecules in polyoxyethylene glycol nonionic detergents

The advantage of aqueous two-phase systems based on polyoxyethylene detergents over other liquid-liquid two-phase systems lies in their capacity to fractionate membrane proteins simply by heating the solution over a biocompatible range of temperatures (20 to 37 degrees C). This permits the peripheral membrane proteins to be effectively separated from the integral membrane proteins, which remain in the detergent-rich phase due to the interaction of their hydrophobic domains with detergent micelles. Since the first reports of this special characteristic of polyoxyethylene glycol detergents in 1981, numerous reports have consolidated this procedure as a fundamental technique in membrane biochemistry and molecular biology. As examples of their use in these two fields, this review summarizes the studies carried out on the topology, diversity, and anomalous behavior of transmembrane proteins on the distribution of glycosyl-phosphatidylinositol-anchored membrane proteins, and on a mechanism to describe the pH-induced translocation of viruses, bacterial endotoxins, and soluble cytoplasmic proteins related to membrane fusion. In addition, the phase separation capacity of these polyoxyethylene glycol detergents has been used to develop quick fractionation methods with high recoveries, on both a micro- and macroscale, and to speed up or increase the efficiency of bioanalytical assays.

Cytoadhesins of Mycoplasma hominis

The mechanism of Mycoplasma hominis adherence to host cells of the urogenital tract was investigated with monoclonal antibodies (MAbs) directed against antigenic surface-localized polypeptides P50, P60, P80, and P100 of cytoadherent M. hominis FBG. A cell enzyme-linked immunosorbent assay was established allowing quantification of cytoadherent mycoplasmas detected by one of the following MAbs: four MAbs directed against P100 (molecular weight, about 100,000), three MAbs against P80, one MAb against P60, and three MAbs against P50. MAb binding to one of the surface proteins resulted in a decrease of mycoplasmal adherence to HeLa cells. To exclude the thesis that this is caused by nonspecific blocking of adherence, P100 and P50 were purified by affinity chromatography and tested instead of intact mycoplasmas in the cell enzyme-linked immunosorbent assay for cytoadherence. Both proteins bound to the surface of the eukaryotic cells. MAb binding to single epitopes of these proteins resulted in inhibition of protein adherence. These experiments strongly suggest that of the four surface-localized proteins at least P100 and P50 are adhesins of M. hominis FBG.

Variation and genetic control of surface antigen expression in mycoplasmas: the Vlp system of Mycoplasma hyorhinis

Surface antigenic diversity in the swine pathogen Mycoplasma hyorhinis is generated by random combinatorial expression and high-frequency phase variation of multiple, size-variant membrane surface lipoproteins (Vlps) which represent the major coat proteins of this wall-less procaryote. The distinctive structural basis for Vlp variation was revealed in a family of several related but divergent vlp genes. These occur in one cluster as single chromosomal copies, each encoding a conserved domain for membrane insertion and lipoprotein processing, and a divergent external domain that changes size by deletion or insertion of repetitive intragenic coding sequences while retaining a distinctive charge motif. Lack of detectable changes in restriction fragment patterns or DNA sequence of vlp structural genes during phase transitions between ON and OFF expression states ruled out long range genomic rearrangements and frameshift mutations as a means of controlling Vlp phase variation. However, highly homologous vlp promoter regions contain a homopolymeric tract of contiguous adenine residues [poly(A)] upstream of the transcriptional start site which is subject to frequent mutations altering its length. These mutations are the only sequence changes detected during phase transitions, and are highly correlated with the expression state of each vlp gene. This suggests a mechanism of transcriptional control regulating Vlp phase variation by critical changes within the poly(A) region affecting the spacing between the -10 and -35 hexamers or a putative regulator binding site. The multiple levels of structural and antigenic diversity embodied in the vlp gene family may provide essential adaptive capabilities for this wall-less microbial pathogen.

Nucleotide sequence analysis and serologic characterization of a 27-kilodalton Mycobacterium intracellulare lipoprotein

Disseminated mycobacteremia resulting from Mycobacterium avium-Mycobacterium intracellulare complex (MAC) infections frequently contribute to the morbidity and mortality seen in AIDS patients. To better understand the immunopathology of MAC disease and to identify molecules that may have potential diagnostic and vaccine utility, an immunoreactive M. intracellulare protein (MI43) and the gene encoding this antigen were characterized. Southern blot hybridizations demonstrated that MI43 gene probes reacted only with genomic DNA from M. intracellulare, M. avium, and Mycobacterium asiaticum and not with DNA isolated from 11 other mycobacterial species. Nucleotide sequence analysis showed that the MI43 gene encodes a 27-kDa protein which contains a consensus bacterial lipoprotein processing sequence. Detergent-phase separations and metabolic labeling with [3H]palmitate also suggested that MI43 is a lipoprotein. Serological assays demonstrated that recombinant MI43 fusion proteins react with sera from M. avium-infected mice, sera from patients with MAC disease, and sera from patients with active tuberculosis. These results further suggest that mycobacterial lipoproteins are important immunogens that should be considered in the development of improved mycobacterial vaccines and diagnostic reagents.

Nucleotide sequence analysis and serologic characterization of the Mycobacterium intracellulare homologue of the Mycobacterium tuberculosis 19 kDa antigen

Disseminated Mycobacterium avium/Mycobacterium intracellulare complex (MAC) disease is a frequent complication in patients with the acquired immune deficiency syndrome (AIDS). In this report, we present the nucleotide sequence of the M. intracellulare MI22 gene. Computer sequence comparisons reveal that the MI22 gene, which encodes a serologically active protein, has 78% DNA sequence identity and 77% protein sequence identity with the seroreactive 19 kDa Mycobacterium tuberculosis lipoprotein antigen. Southern blot hybridizations indicate that an MI22 gene probe binds similar-sized restriction fragments in M. tuberculosis and M. intracellular genomic DNA. In addition, immunoblot analyses demonstrate that MI22 is recognized by sera from tuberculosis patients. These data further support the existence of 19 kDa MAC and M. tuberculosis protein homologues. Phase partitioning experiments and the presence of a consensus lipid modification site in the deduced MI22 protein sequence strongly suggest that M122 is also a lipoprotein. Comparative analyses of these mycobacterial antigenic homologues may provide the basis for the design of species-specific diagnostic reagents.

Comparison of Mycoplasma bovis strains based on SDS-PAGE and immunoblot protein patterns

Whole-cell protein patterns generated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) were compared for 34 isolates of Mycoplasma bovis. A high degree of similarity between most of the strains was established with strain-to-strain differences mainly confined to quantitative variations of certain protein bands, particularly in the molecular weight regions of 64-68, 55 and 26 kD. Two of the isolates provided more deviating patterns. Hydrophobic membrane protein fractions of the strains as prepared by Triton X-114 phase partitioning were compared by SDS-PAGE, which confirmed some of the characteristic strain features found with whole-cell proteins. The immunoblot analysis revealed that up to 20 of the 50-55 discrete protein bands detected in SDS-PAGE patterns were recognized to be antigenic by rabbit and bovine hyperimmune sera. It is concluded that the same set of major antigens is present in all strains investigated, but amounts of individual constituents may be differing.

Electron-microscopic study of the effect of various extractants on the morphology of Coxiella burnetii

This paper presents the results of the effect of trichloroacetic acid (TCA) at two different temperatures and the effect of a mixture of detergents (D) on Coxiella burnetii. Both TCA and D caused a large destruction of C. burnetii cells. In both cases complexes of high-molar-mass components from the outer membrane were extracted. In the D case not only proteins but a mixture with other high-molar-mass structures were released from the destroyed cells. By extraction of TCA, the antigenic complex composed of lipopolysaccharides (LPS), proteins and phospholipids was released. The effect of the D mixture on C. burnetii causes their complete destruction. The TCA causes a surface destruction of cells but it does not cause complete disintegration. The small-cell variants (SCV) in both cases were shown to be more stable compared to the large-cell variants (LCV).

Decreased metabolism and viability of Mycoplasma hominis induced by monoclonal antibody-mediated agglutination

Monoclonal antibodies (MAbs) were generated against lysates of clinical Mycoplasma hominis isolates. Three of these, designated BG2, BA10, and FE6, recognized an integral membrane protein of M. hominis with an apparent molecular weight of 50,000 (p50). Electron microscopy studies demonstrated that this protein is distributed evenly over the cell surface. These anti-p50 MAbs were species specific for M. hominis; they reacted with 42% of 126 tested clinical M. hominis isolates and showed no reactivity to heterologous mycoplasma species. Immunoblot analysis after limited proteolysis of purified p50 demonstrated that the three MAbs reacted with different epitopes of the protein. Unlike BA10 and FE6, MAb BG2 induced a decrease in arginine metabolism and a reduction of CFU in metabolic inhibition tests. F(ab)2 fragments of MAb BG2 showed the same inhibitory effect as the intact MAb molecule, while Fab and Fc fragments had no influence on vital functions. Preincubation of the mycoplasmas with MAb BG2 followed by trypsin treatment yielded the same amount of CFU as the control without antibodies. In conclusion, the cell aggregates were resolved by the trypsin treatment. These experiments and tests with the antibody fragments led to the conclusion that only the intact MAb structure or the F(ab)2 structure had metabolic inhibition potential and that the observed metabolism inhibition as well as the apparent decrease in viability were a result of agglutination by MAb BG2.

The Vlp system of Mycoplasma hyorhinis: combinatorial expression of distinct size variant lipoproteins generating high-frequency surface antigenic variation

Isogenic populations of Mycoplasma hyorhinis undergo in vitro high-frequency phase variation in the expression of surface lipoproteins; these products also vary markedly in size through changes in periodic protein structure (R. Rosengarten and K.S. Wise, Science 247:315-318, 1990). In this report, we rigorously define three distinct translation products comprising the Vlp (variable lipoprotein) system of M. hyorhinis SK76 and establish parameters of Vlp structural diversity and expression that distinguish the Vlp system from previously described examples of antigenic variation. VlpA, VlpB, and VlpC are prominent amphiphilic membrane lipoproteins characterized by detergent-phase fractionation and metabolic labeling with [35S]cysteine and [3H]palmitate. VlpA is distinguished from VlpB and VlpC by its selective labeling with [35S]methionine; VlpB and VlpC are distinguished by specific epitopes defined by surface-binding monoclonal antibodies (MAbs); a third MAb defines a surface epitope shared by VlpB and VlpC (but absent from VlpA). Each Vlp displays 12 to 30 spontaneous size variant forms comprising a periodic ladder that could also be generated by partial trypsin digestion of individual Vlp size variants. Different periodic intervals within VlpB and VlpC further distinguish these two products structurally. Mycoplasma colony opacity correlates inversely with Vlp size. Each Vlp undergoes independent, oscillating high-frequency phase variation in isogenic populations and can be expressed individually or concomitantly with other Vlps in a noncoordinate manner. All seven possible combinations of these three products were observed; however, no variants were found that lacked a Vlp. High-frequency size variation of each Vlp superimposed on combinatorial diversity in Vlp expression yields greater than 10(4) possible structurally distinct Vlp mosaics, of which 104 were documented along with 24 of 42 possible transitions among the seven Vlp combinations. In addition to these features, VlpA, VlpB, and VlpC were specifically recognized by serum antibodies from swine with experimental M. hyorhinis SK76-induced arthritis, indicating expression and immunogenicity of Vlps in the natural host. The structure and variation of Vlps and their known involvement in MAb-mediated modulation of mycoplasma-infected host cell properties and mycoplasma killing are discussed in relation to the surface architecture and adaptive potential of the wall-less mycoplasmas.

Palmitoylated proteins in Ureaplasma urealyticum

After incubation of Ureaplasma urealyticum serotype 8 in the presence of 3H-labeled palmitic acid, about 25 acylated proteins were detected by electrophoresis and fluorography. Of these, at least six were shown to be antigenic by immunoprecipitation of solubilized palmitate-labeled cells with a homologous polyclonal serum. These six included the serotype 8-specific surface-expressed 96-kDa antigen. After phase partition of palmitate-labeled cells with Triton X-114, all but six acylated proteins partitioned entirely into the detergent phase. The others, including the 96-kDa antigen, partitioned preferentially into the detergent phase and were apparently amphipathic. These results are consistent with the acylated proteins being mainly membrane associated.

Fast and simple procedure for the detection of cell culture mycoplasmas using a single monoclonal antibody

The detection of mycoplasmas in cell cultures is still a problem, especially in those laboratories in which the detection and identification of microorganisms is not established as a routine procedure. In our laboratory, monoclonal antibodies (mAbs) have been prepared to Acholeplasma laidlawii, Mycoplasma hyorhinis, Mycoplasma orale, Mycoplasma arginini and Mycoplasma salivarium. 30 mAbs were obtained and one of these, designated CCM-2, was shown to bind to all five mycoplasma species. It also bound to Mycoplasma fermentans, Mycoplasma hominis and to all wild types (n = 54), isolated from cell cultures submitted to our laboratory. The mAb was used in a immunofluorescent assay (IF) and the method correlated with the microbiological assay. Using this mAb immunofluorescent staining of cells is a fast and simple procedure for mycoplasma detection in cell cultures.

Polypeptide and antigenic variability among strains of Mycoplasma ovipneumoniae demonstrated by SDS-PAGE and immunoblotting

Comparison of the polypeptide patterns of 22 isolates of M. ovipneumoniae by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a marked degree of heterogeneity with only limited groupings identifiable. Of the 50 major polypeptides identified in one strain (956/2), 35 were shown to be antigenic using immunoblotting with a homologous polyclonal serum. Radioimmune precipitation of 125I-surface-labelled proteins and phase partition using Triton X-114 detergent indicated that these were membrane associated. Cross-reactivity between the isolates was examined by immunoblotting using one polyclonal serum and four monoclonal antibodies (MAbs), all raised against strain 956/2. The polyclonal serum revealed considerable antigenic heterogeneity, but at least nine major antigens were conserved across all isolates. Two MAbs cross-reacted with all 22 strains, but the other two MAbs allowed some differentiation of the strains. One (MO/3) divided the isolates into groups of 16 and 6 based on the presence of absence of a 26-kDa antigen. All strains isolated from sheep with pulmonary adenomatosis fell into the smaller group and did not possess the 26-kDa antigen.

Serotype 8- and serocluster-specific surface-expressed antigens of Ureaplasma urealyticum

The polypeptides of all 14 serotypes of Ureaplasma urealyticum were analyzed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining. The electrophoretic patterns did not allow ready discrimination of individual serotypes or seroclusters. The analysis of the antigens of serotype 8 was reported previously (B. L. Precious, D. Thirkell, and W. C. Russell, J. Gen. Microbiol. 133:2659-2676, 1987). In this study, three of the surface-expressed membrane antigens of 16, 17, and 96 kilodaltons were further investigated, and monoclonal antibodies were raised against these three polypeptides. The major 96-kilodalton polypeptide was serotype 8 specific, and the 16-kilodalton polypeptide was present only in the larger serocluster. We describe monoclonal antibody probes that unequivocally differentiate serotype 8 from the other serotypes and that separate the two seroclusters of the organism.

Subunit structure of the variable V-1 antigen of Mycoplasma pulmonis

It was previously shown that multiple structural variants of the V-1 antigen (variable antigen 1) of Mycoplasma pulmonis could be found within a single strain. This antigen is unusual in that it produces a ladder pattern after sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The present study showed that some variants of V-1 could be extracted into the aqueous phase of a phenol-H2O system. Analysis with anti-V-1 monoclonal antibodies showed that the phenol-H2O-extracted V-1 had a regular spacing of 3.1 kilodaltons (kDa) between bands and trypsinization of this extracted V-1 resulted in the gradual symmetrical collapse (2.9-kDa increments) of the ladder into a single band, suggesting the presence of multiple identical subunits within the V-1 structure. The upper band from the phenol-H2O-extracted V-1 was isolated and analyzed by SDS-polyacrylamide gel electrophoresis immunoblotting, resulting in the regeneration of the original ladder pattern with 3.1-kDa spacing between bands. When V-1 was boiled for increasing times in the presence of SDS, the staining intensity of the upper band decreased with the concurrent appearance of additional lower-molecular-weight bands. Finally, by using whole cells, it was found that the lower-molecular-weight species of the ladder pattern selectively partitioned into the hydrophobic phase of a Triton X-114 phase partitioning system, and the higher-molecular-weight bands were found in the aqueous phase. These data indicate that the V-1 bands are composed of subunits which may aggregate via hydrophobic interactions and that these aggregates at least partially dissociate when exposed to harsh denaturing conditions, resulting in the characteristic ladder pattern of V-1.

Lipid-modified surface protein antigens expressing size variation within the species Mycoplasma hyorhinis

Monoclonal antibodies (MAbs) previously shown to recognize distinct epitopes selectively expressed on the surface of some Mycoplasma hyorhinis strains were used to define two discrete sets of lipid-modified membrane surface proteins showing marked size variation within this species. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis of Triton X-114 phase-fractionated proteins from six isolates of M. hyorhinis defined a set of amphiphilic integral membrane proteins of 23, 50, and 55 kilodaltons (kDa) recognized on respective isolates by one MAb and a second set of integral proteins of 88, 120, and 100 to 150 kDa recognized by another MAb. The first group of proteins all contained a common, amphiphilic 18-kDa limit tryptic polypeptide bearing the epitope. The size- and strain-variant surface antigens identified by the MAbs were shown to be lipid-modified proteins. Phase fractionation of [3H]palmitate-labeled organisms revealed numerous 3H-labeled proteins in all isolates, which partitioned exclusively into the hydrophobic phase. These proteins generally showed pronounced size variation among isolates and included the antigen variants recognized by the two MAbs, as demonstrated directly by immunoprecipitation of correspondingly sized 3H-labeled proteins from each isolate. A third MAb recognized an invariant, lipid-associated surface protein of 70 kDa on all M. hyorhinis isolates. Covalent modification of lipid-associated proteins was confirmed by identifying 3H-labeled methyl palmitate after acid methanolysis of Triton X-114 phase proteins derived from [3H]palmitate-labeled organisms. However, removal of covalently bound lipid from chloroform-methanol-extracted proteins by alkaline hydroxylamine was selective; complete removal was observed with only a few proteins, possibly including the 120-kDa form of one antigen variant. This suggested potential differences in the nature of covalent linkage among lipid-modified M. hyorhinis surface antigens. Intraspecies antigen variants described here in M. hyorhinis share some characteristics with size-variant antigens reported in phylogenetically related gram-positive eubacteria and may contribute to phenotypic diversification and differences in pathogenicity of mycoplasmas.

Selective release of the Treponema pallidum outer membrane and associated polypeptides with Triton X-114

The effects of the nonionic detergent Triton X-114 on the ultrastructure of Treponema pallidum subsp. pallidum are presented in this study. Treatment of Percoll-purified motile T. pallidum with a 1% concentration of Triton X-114 resulted in cell surface blebbing followed by lysis of blebs and a decrease in diameter from 0.25-0.35 micron to 0.1-0.15 micron. Examination of thin sections of untreated Percoll-purified T. pallidum showed integrity of outer and cytoplasmic membranes. In contrast, thin sections of Triton X-114-treated treponemes showed integrity of the cytoplasmic membrane but loss of the outer membrane. The cytoplasmic cylinders generated by detergent treatment retained their periplasmic flagella, as judged by electron microscopy and immunoblotting. Recently identified T. pallidum penicillin-binding proteins also remained associated with the cytoplasmic cylinders. Proteins released by Triton X-114 at 4 degrees C were divided into aqueous and hydrophobic phases after incubation at 37 degrees C. The hydrophobic phase had major polypeptide constituents of 57, 47, 38, 33-35, 23, 16, and 14 kilodaltons (kDa) which were reactive with syphilitic serum. The 47-kDa polypeptide was reactive with a monoclonal antibody which has been previously shown to identify a surface-associated T. pallidum antigen. The aqueous phase contained the 190-kDa ordered ring molecule, 4D, which has been associated with the surface of the organisms. Full release of the 47- and 190-kDa molecules was dependent on the presence of a reducing agent. These results indicate that 1% Triton X-114 selectively solubilizes the T. pallidum outer membrane and associated proteins of likely outer membrane location.

Identification and localization of integral membrane proteins of virulent Treponema pallidum subsp. pallidum by phase partitioning with the nonionic detergent triton X-114

Integral membrane proteins of Treponema pallidum subsp. pallidum (T. pallidum) were identified by phase partitioning with the nonionic detergent Triton X-114; antigens with apparent molecular masses of 47, 38, 36, 34, 32, 17, and 15 kilodaltons (kDa) were identified in the detergent phase. Immunoblotting with murine monoclonal antibodies directed against pathogen-specific 47- and 34-kDa T. pallidum antigens confirmed their presence in the detergent phase. Endoflagellar proteins of T. pallidum were not detected in immunoblots of detergent-phase proteins when monospecific antisera directed against endoflagella of the nonpathogenic T. phagedenis biotype Reiter were used. At detergent concentrations (0.02 and 0.1%) which appeared to solubilize selectively the outer membranes of treponemes radiolabeled with 35S in vitro, limited amounts of detergent-phase proteins were immunoprecipitated. Greater amounts of detergent-phase proteins were extracted at higher detergent concentrations (0.5 and 2.0%) which resulted in both outer membrane solubilization and ultrastructural derangements of the residual cytoplasmic bodies. Furthermore, Triton X-114 extraction of both intact treponemes and organisms without outer membranes yielded detergent phases with similar protein profiles. The results of these experiments indicate that the hydrophobic proteins identified by Triton X-114 are not located exclusively in the T. pallidum outer membrane. The results are also consistent with the hypothesis that the T. pallidum outer membrane is a protein-deficient lipid bilayer.

Association of lipids with integral membrane surface proteins of Mycoplasma hyorhinis

Triton X-114 (TX-114)-phase fractionation was used to identify and characterize integral membrane surface proteins of the wall-less procaryote Mycoplasma hyorhinis GDL. Phase fractionation of mycoplasmas followed by analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed selective partitioning of approximately 30 [35S]methionine-labeled intrinsic membrane proteins into the TX-114 phase. Similar analysis of [3H]palmitate-labeled cells showed that approximately 20 proteins of this organism were associated with lipid, all of which also efficiently partitioned as integral membrane components into the detergent phase. Immunoblotting and immunoprecipitation of TX-114-phase proteins from 125I-surface-labeled cells with four monoclonal antibodies to distinct surface epitopes of M. hyorhinis identified surface proteins p120, p70, p42, and p23 as intrinsic membrane components. Immunoprecipitation of [3H]palmitate-labeled TX-114-phase proteins further established that surface proteins p120, p70, and p23 (a molecule that mediates complement-dependent mycoplasmacidal monoclonal antibody activity) were among the lipid-associated proteins of this organism. Two of these proteins, p120 and p123, were acidic (pI less than or equal to 4.5), as shown by two-dimensional isoelectric focusing. This study established that M. hyorhinis contains an abundance of integral membrane proteins tightly associated with lipids and that many of these proteins are exposed at the external surface of the single limiting plasma membrane. Monoclonal antibodies are reported that will allow detailed analysis of the structure and processing of lipid-associated mycoplasma proteins.

Major membrane surface proteins of Mycoplasma hyopneumoniae selectively modified by covalently bound lipid

Surface protein antigens of Mycoplasma hyopneumoniae were identified by direct antibody-surface binding or by radioimmunoprecipitation of surface 125I-labeled proteins with a series of monoclonal antibodies (MAbs). Surface proteins p70, p65, p50, and p44 were shown to be integral membrane components by selective partitioning into the hydrophobic phase during Triton X-114 (TX-114)-phase fractionation, whereas p41 was concomitantly identified as a surface protein exclusively partitioning into the aqueous phase. Radioimmunoprecipitation of TX-114-phase proteins from cells labeled with [35S]methionine, 14C-amino acids, or [3H] palmitic acid showed that proteins p65, p50, and p44 were abundant and (with one other hydrophobic protein, p60) were selectively labeled with lipid. Covalent lipid attachment was established by high-performance liquid chromatography identification of [3H]methyl palmitate after acid methanolysis of delipidated proteins. An additional, unidentified methanolysis product suggested conversion of palmitate to another form of lipid also attached to these proteins. Alkaline hydroxylamine treatment of labeled proteins indicated linkage of lipids by amide or stable O-linked ester bonds. Proteins p65, p50, and p44 were highly immunogenic in the natural host as measured by immunoblots of TX-114-phase proteins with antisera from swine inoculated with whole organisms. These proteins were antigenically and structurally unrelated, since hyperimmune mouse antibodies to individual gel-purified proteins were monospecific and gave distinct proteolytic epitope maps. Intraspecies size variants of one surface antigen of M. hyopneumoniae were revealed by a MAb to p70 (defined in strain J, ATCC 25934), which recognized a larger p73 component on strain VPP11 (ATCC 25617). In addition, MAb to internal, aqueous-phase protein p82 of strain J failed to bind an analogous antigen in strain VPP11. These studies establish that a highly restricted set of distinct, lipid-modified hydrophobic membrane proteins are major surface antigens of M. hyopneumoniae and that structural variants of surface antigens occur within this species.