Localization of the Mycoplasma pneumoniae cytadherence-accessory proteins HMW1 and HMW4 in the cytoskeletonlike Triton shell

The location of the cytadherence-accessory high-molecular weight proteins 1 and 4 (HMW1/4) within Mycoplasma pneumoniae cells has been studied by both biochemical and electron microscopic techniques. Peptide mapping studies demonstrated that HMW1/4 share almost identical peptide profiles, suggesting that the two proteins are structurally related. Examination of thin sections of M. pneumoniae with antibodies to HMW1/4 and colloidal gold particles revealed distinct labeling of the filamentous extensions of the mycoplasma cells. Labeling was absent on thin sections of a cytadherence-deficient variant lacking HMW1/4. HMW1/4 partitioned in the detergent-insoluble fraction following Triton X-100 extraction, and analysis by sucrose density gradient centrifugation suggested that HMW1/4 are part of a high-molecular-weight, multiprotein complex. These results were confirmed by immunogold labeling of Triton X-100-extracted M. pneumoniae cells incubated with antibodies to HMW1/4: gold particles bound in specific clusters to detergent-insoluble filaments. Finally, immunogold labeling of whole cells revealed that HMW1/4 are exposed on the cell surface, although to a lesser degree than on the cell interior. These findings indicate that HMW1/4 are membrane proteins associated with the cytoskeletonlike triton shell of M. pneumoniae and localized primarily in the filamentous extensions of the mycoplasma cells.

Disulfide-linked protein associated with Mycoplasma pneumoniae cytadherence phase variation

Wild-type Mycoplasma pneumoniae possessed a protein with a very high molecular weight under nonreducing conditions (greater than 340,000; designated HMW5); this protein was absent from a noncytadhering phase variant lacking HMW1, 2, 3, and 4. When examined by two-dimensional nonreducing-reducing gel electrophoresis, HMW5 dissociated to yield a single polypeptide spot of molecular weight 190,000 that comigrated with cytadherence phase-variable protein HMW2. Extraction of wild-type mycoplasmas with Triton X-100 revealed the exclusive partitioning of HMW5 with the detergent-insoluble cytoskeletonlike triton shell.

Evidence for occurrence of passively adsorbed I antigen activity on a cultured strain of Mycoplasma pneumoniae

The aim of this study was to investigate whether I antigen occurs in association with Mycoplasma pneumoniae in a form that may be immunogenic during natural infection or experimental immunization. I antigen activity was detected by radioimmunoassay in suspensions of M. pneumoniae MY11965 and in the soluble phase of mycoplasma lysates prepared with Triton X-100. There was evidence for the occurrence of I antigen in at least two macromolecular forms. The first form partitioned in the lipid phase following chloroform-methanol extraction and chromatographed on thin-layer chromatograms as a ceramide decasaccharide. The second form was associated with the residue after lipid extraction and was solubilized by treatment with sodium dodecyl sulfate or pepsin; this component was tentatively designated a glycoprotein or polysaccharide and was not investigated further. In a lipid extract from mycoplasmas that had been surface labeled by the galactose oxidase-NaB3H4 method, two 3H-labeled glycolipids were detected as minor components which chromatographed on thin-layer chromatograms in the region of an authentic I-active ceramide decasaccharide. However, no significant radioactivity was incorporated into glycolipids after metabolic labeling with [3H]glucosamine. These observations suggested that the mycoplasmas contained surface-associated glycolipids with I antigen activity that were of exogenous origin. This was supported by the observations that horse, rabbit, and fetal calf sera contained I antigen activity and that the I antigen activity in M. pneumoniae cultures reflected the levels found in the sera included in the culture media. From rabbit serum, which expressed the highest antigen activity, an I-active glycolipid was isolated that chromatographed as a ceramide decasaccharide. I-active substances passively adsorbed onto M. pneumoniae are potentially immunogenic. However, we consider these unlikely to be the main stimulus for autoantibody production in natural infection, since the autoantibodies elicited are restricted to the I carbohydrate antigen and there is a lack of antibodies to other glycolipids that may be adsorbed from serous and cellular components of the host tissues. In our view, the more likely stimulus is the specific complex formed between the mycoplasma and the sialo-oligosaccharide receptors of the Ii antigen type, as suggested previously.

Identification of a 32-kilodalton protein of Mycoplasma pneumoniae associated with hemadsorption

Monoclonal antibodies directed against a 32-kilodalton (kDa) protein of Mycoplasma pneumoniae have been used to characterize a hemadsorption-negative (HA-) mutant class whose protein profile was previously indistinguishable from the wild-type, hemadsorbing (HA+) strain. Electron microscopy and colloidal gold labeling techniques were applied for ultrastructural analysis of the 32-kDa protein. Results indicate that this protein clusters in the tip structure of M. pneumoniae (HA+) wild-type organisms. Additionally, the protein is precipitated by infected hamster sera.

Electroelution of fixed and stained membrane proteins from preparative sodium dodecyl sulfate-polyacrylamide gels into a membrane trap

The membrane trap is a new device for the electroelution of all kinds of charged macromolecules from gels. Instead of dialysis membranes, the membrane trap uses a new membrane. Retention of macromolecules in an electric field by dialysis membranes depends on the presence of sodium dodecyl sulfate (SDS) in the buffer. The new membrane retains all charged macromolecules larger than approximately 5000 Da without adsorbing them, independent of the use of SDS. Here we report the electroelution of five different lipophilic membrane proteins (33 to 193 kDa) of Mycoplasma pneumoniae from preparative SDS-polyacrylamide gels into a 300-microliter recovery volume. After an 8-h elution period, recovery ranged from 80 (193 kDa) to 97% (33 kDa). The "losses" were generally due to proteins still remaining in the gel slice. All of the eluted proteins tested in a dot-blot assay proved to be antigenically active. The advantages of the device described here are easy handling (insertion of membranes, open system), quantitative recovery, and high reproducibility of the elution results.

Detection of the major adhesin P1 in triton shells of virulent Mycoplasma pneumoniae

Filamentous structures designated Triton shells were obtained from virulent Mycoplasma pneumoniae by treatment with Triton X-100. Monoclonal antibodies directed against M. pneumoniae were used in conjunction with radioimmunoprecipitation and Western blotting to detect immunologically reactive polypeptides in Triton shells. The major adhesin, protein P1, was associated with these structures.

Detection of Mycoplasma pneumoniae adhesin (P1) in the nonhemadsorbing population of virulent Mycoplasma pneumoniae

Mycoplasma pneumoniae organisms possessing a hemadsorbing-negative (HA-) phenotype comprise more than 50% of the population of virulent M. pneumoniae cultures. Monoclonal antibody to P1, the major adhesin of M. pneumoniae reacts with this HA- mycoplasma fraction based upon radioimmunoprecipitation and immunoblotting. Demonstration of P1 in the entire mycoplasma population suggests that topological organization of this adhesin in the membrane or the physiological state of the mycoplasmas may determine hemadsorbing capabilities.

Analysis of polypeptides of mutants of Mycoplasma pneumoniae that lack the ability to haemadsorb

Haemadsorption-negative mutants of Mycoplasma pneumoniae were isolated which varied in their capacity to adsorb erythrocytes of various animal species suggesting adherence to erythrocytes is mediated by different binding mechanisms. Trypsin treatment of the wild-type strain resulted in loss of haemadsorbing activity; several polypeptides, some of which regenerated with haemadsorbing activity following further incubation, were also trypsin sensitive. The haemadsorption-negative mutants could be divided into two groups according to their polypeptide pattern. In the first group (11 mutants) the PAGE pattern was identical to that of the wild-type strain. The second group comprised 7 mutants which differed from the wild-type by lack of one or more polypeptides with molecular weights of 190 000, 90 000 or 40 000. During growth attachment to glass was weak or absent in the mutants. Surface hydrophobicity as measured by hydrophobic-interaction chromatography was nearly comparable in mutants and parent strain.

Reacquisition of specific proteins confers virulence in Mycoplasma pneumoniae

Hemadsorbing revertants were isolated from spontaneous hemadsorption-negative, avirulent mutants of Mycoplasma pneumoniae. The revertants simultaneously reacquired specific proteins absent in their homologous mutants, along with neuraminidase-sensitive adherence to the respiratory epithelium and virulence. Peptide mapping and immunological analysis indicated no precursor-product relationships among certain of these proteins.

Location of attachment moiety on Mycoplasma pneumoniae

Mycoplasma pneumoniae initiates infection in the human host by attachment to respiratory epithelium. The organism attaches by a specialized terminal structure. Monoclonal antibodies to an organism surface protein (P1) inhibited attachment to respiratory epithelium and were localized to the tip structure by a ferritin antibody label. The P1 protein was degraded by trypsin treatment to smaller polypeptides that possessed the same antigenic determinants as the larger P1 protein when reacted with the specific monoclonal antibody, and evidence has been provided for the existence of multiple antigenic determinants on the attachment protein.

Purification of attachment moiety: a review

Mycoplasma pneumoniae and M. gallisepticum possess binding sites of protein nature which mediate attachment to neuraminidase-sensitive regions on both respiratory epithelium and red blood cells. The binding sites of these organisms are similar though not identical. Several approaches were applied for the isolation of the binding sites. Of these, the use of affinity chromatography yield the least complex protein fraction. We have recently been using sialoglycopeptides as the ligands in affinity chromatography. The availability of monoclonal antibodies which inhibit the attachment of M. pneumoniae to host cells should provide a very specific tool for the isolation of the attachment moiety. It should be mentioned that not all mycoplasmas adhere to host cells via sialic acid specific receptors, and other approaches should be developed to study these mycoplasmas' attachment moieties.

Mycoplasma and bacterial proteins resembling contractile proteins: a review

The basis of gliding motility in prokaryotes including certain mycoplasmas and the ability of mycoplasmas to retain their characteristic cell shapes in the absence of a supporting cell wall is unexplained. This review examines the available studies describing proteins resembling contractile proteins and cytoskeletal proteins in prokaryotes. Proteins with a significant degree of amino acid sequence homology to the myofibrillar proteins actin and myosin Al light chain and to tropomyosin have been described in prokaryotes. In addition, protein preparations from Mycoplasma pneumoniae have been shown to bind heavy meromyosin fragments, anti-actin antibody, and phalloidin; however, it remains to be proved that proteins in these preparations sharing properties with actin are synthesized by the mycoplasma.

Mycoplasma pneumoniae attachment: competitive inhibition by mycoplasmal binding component and by sialic acid-containing glycoconjugates

Attachment of Mycoplasma pneumoniae to human WiDr cell culture monolayers was examined by using radiolabeled M. pneumoniae. The amount of attachment was proportional to the density of the WiDr cells and to the concentration of M. pneumoniae in the assay. Saturation of the monolayers was achieved with 40 micrograms of virulent strain M129 per assay, whereas binding of avirulent strain B176 was 70% less than that of strain M129. A competitive attachment inhibition assay was used to measure specific binding component activity. Attachment was inhibited when WiDr cells were pretreated with unlabeled virulent strain M129, whereas avirulent noncytadsorbing strain B176 did not inhibit attachment as well as the virulent strain. A protein-rich extract prepared from virulent, cytadsorbing strains of M. pneumoniae also inhibited attachment. The amount of inhibition was dependent on the amount of extract used, and units for binding component activity in the extract were calculated from the competitive attachment inhibition assays. The competitive attachment inhibition assay was also used to investigate the nature of the receptor site on the WiDr cells. Attachment was inhibited when the radiolabeled M. pneumoniae suspensions were pretreated with human sialoglycoproteins, such as orosomucoid and ceruloplasmin, and bovine gangliosides. These findings support the present concept that the mammalian receptor site for M. pneumoniae is a sialic acid-containing glycoprotein.

Molecular basis for cytadsorption of Mycoplasma pneumoniae

Hemadsorbing (HA+) virulent Mycoplasma pneumoniae and spontaneously derived nonhemadsorbing (HA-) avirulent mutants were compared by biochemical and ultrastructural techniques in an attempt to understand the molecular basis for cytadsorption. Lactoperoxidase-catalyzed iodination of intact mycoplasmas indicated that both virulent and avirulent mycoplasmas displayed similar surface protein patterns. A specific external protein, P1 (molecular weight, 165,000), previously implicated as a major ligand mediating attachment, was readily detected in HA+ and HA- mycoplasma strains. However, immunoferritin electron microscopy, with monospecific antibody against P1, revealed that differences in P1 topography existed among these strains. Only virulent mycoplasmas exhibited high concentrations of P1 at the terminal organelle. Avirulent mycoplasmas which possessed P1 showed no P1 clustering at the terminus. Both virulent M. pneumoniae and avirulent P1-containing mutants possessed numerous less dense P1 regions along the mycoplasma surface. Not surprisingly, an HA- mutant lacking P1 exhibited only background immunoferritin labeling. Negative staining of intact mycoplasmas revealed a well-defined, naplike terminus (associated with P1 clusters) confined at the tip of virulent M. pneumoniae. Previous characterization of HA+ virulent and HA- avirulent strains of M. pneumoniae by one- and two-dimensional polyacrylamide gel electrophoresis suggests that identified groups of mycoplasma proteins, lacking in specific HA- mycoplasmas, regulate the physical arrangement of P1 and the ultrastructure of the terminus, thus influencing adherence to the respiratory epithelium and virulence.

Mycoplasma pneumoniae proteins that selectively bind to host cells

Mycoplasma pneumoniae proteins that bind to hamster trachea epithelial cells were identified by incubating 125I-labeled, detergent-solubilized mycoplasmas with glutaraldehyde-fixed host cells. Analysis of the bound fraction by gel electrophoresis and autoradiography revealed that proteins P1, P2, and HMW3 (molecular weights, 165,000, 110,000, and 140,000, respectively), previously implicated in attachment, were among the predominant species. Unlabeled mycoplasma preparations competed with the binding of radiolabeled proteins, suggesting the involvement of a limited number of receptor sites on the host cells.

Release of Mycoplasma pneumoniae substances after phagocytosis by guinea pig alveolar macrophages

Antibody-opsonized Mycoplasma pneumoniae cells with various radioactive markers were sedimented onto monolayers of guinea pig alveolar macrophages (AM). After 2 h of incubation, about 50% of the activity of [3H]palmitate-labeled mycoplasmas was associated with AM. Nonspecific attachment of the opsonized mycoplasmas to AM-free plastic surface areas was negligible. The occurrence of phagocytosis was proven by electron microscopy and monitoring of AM surface-bound antigen by 125I-labeled F(ab)2 fragments. The activity of [3H]palmitic acid-labeled mycoplasmas was only slowly released into the supernatant. About 55% of the activity remained AM-associated up to 70 h after phagocytosis. After phagocytosis of [3H]thymidine-labeled cells, about 70% of the radioactivity found non-precipitable by trichloracetic acid. 3H-amino acid-labeled protein was released to 50% within 8 h. Supernatants and AM were tested for M. pneumoniae antigen with enzyme-linked immunosorbent assay. Considerable amounts of antigenically active material could be found in the supernatant within 8 h. This antigen was totally inactivated by heat (80 degrees C). Trypsin treatment (1 mg/ml, 10 min) reduced the antigenicity by 80%. The results suggest a selective release of microbial material after phagocytosis.

Attachment of Mycoplasma pneumoniae to hamster tracheal organ cultures, tracheal outgrowth monolayers, human erythrocytes, and WiDr human tissue culture cells

Virulent strains of Mycoplasma pneumoniae, PI-1428 and M129, were radiolabeled wtih [3H]palmitic acid or [3H]thymidine and examined for attachment to hamster tracheal organ cultures, tracheal outgrowth monolayers, human O-positive erythrocytes, and human WiDr carcinoma cell cultures. Although attachment to each cell substrate was readily detected, the WiDr cell culture monolayers provided the most satisfactory substrate for quantitating mycoplasma attachment. Serious technical limitations were encountered with each of the other substrates that we examined; these limitations interfered with reproducibility or sensitivity and rendered tracheal organ cultures and erythrocyte suspensions unsuitable for routine attachment and attachment inhibition assays. Moreover, the WiDr cell monolayer was the most sensitive substrate for determining attachment inhibition activity in protein-containing extracts prepared from M. pneumoniae. The significance of these findings is discussed.

Identification of Mycoplasma pneumoniae proteins associated with hemadsorption and virulence

Twenty-two mutants of Mycoplasma pneumoniae spontaneously deficient in hemadsorption were isolated. Examination of mutant protein profiles by one- and two-dimensional polyacrylamide gel electrophoresis permitted the grouping of these mutants into four classes. The largest class of mutants was deficient in four high-molecular-weight proteins (215,000, 210,000, 190,000, and 140,000). A second class of mutants lacked three proteins previously designated A, B, and C (72,000, 85,000, and 37,000, respectively). A single mutant, in addition to lacking proteins A, B, and C, was missing a fourth protein of 165,000 molecular weight. The remaining mutants exhibited protein profiles apparently identical to that of the wild-type strain. All mutant strains attached to the respiratory epithelium of hamster tracheal rings in vitro at reduced levels; however, mutants lacking proteins A, B, and C recognized only neuraminidase-insensitive receptors. None of the mutants tested produced detectable pneumonia in intranasally inoculated hamsters, although one mutant class demonstrated low-level survival in vivo.

Long-chain fatty acid perturbations in Mycoplasma pneumoniae

The fatty acid content of Mycoplasma pneumoniae increased 2.5- to 9.6-fold when the growth medium was supplemented with a saturated, unsaturated, or beta-hydroxy fatty acid, the greatest increase occurring with palmitic acid. The amount of each supplemented fatty acid found within this organism was 2.8 to 5.5% of the total fatty acid content; the exception was palmitic acid. Up to 57% of the palmitic acid was utilized from the supplemented medium, whereas only 0.2 to 10% of the other fatty acids was utilized. Chromatographic and isotopic analyses revealed that 22% of the labeled palmitic acid incorporated from the palmitic acid-supplemented medium remained free in this organism. Also, even though complex lipid synthesis increased a minimum of 3.8-fold under these conditions, this mycoplasma continued to incorporate intact complex lipids from the growth medium. Bacteriostatic and bactericidal studies which used high concentrations of various long-chain fatty acids showed that only palmitic, myristic, and beta-hydroxydecanoic acids were not bactericidal. The addition of palmitic acid to the growth medium resulted in the formation of exceedingly long, filamentous cells in approximately 25% of the population. Osmotic fragility and electron spin resonance spectroscopy studies showed a correlation among this increased fatty acid content, decreased membrane fluidity, and the increased osmotic fragility of palmitic acid-grown cells. In addition, these cells had a lowered cholesterol content. The effect of such compositional changes on osmotic fragility is discussed in this paper. Finally, the profound increase in the total fatty acid content of palmitic acid-grown cells altered neither sensitivity to tetracycline or erythromycin nor the amount of hydrogen peroxide secreted.

Isolation of binding sites to glycophorin from Mycoplasma pneumoniae membranes

Sialoglycoproteins are major receptor sites for attachment of Mycoplasma pneumoniae to respiratory epithelium and erythrocytes (RBC). We used glycophorin, the major sialoglycoprotein of human RBC, as a ligand in affinity chromatography for the isolation of the binding sites from M. pneumoniae membranes. Membranes isolated from M. pneumoniae cells, radioiodinated by the lactoperoxidase technique, were treated with 0.5% deoxycholate. The insoluble residue, exhibiting an increased capacity to bind to RBC, was solubilized by 0.1% sodium dodecyl sulfate. The solubilized material was subjected to chromatography on a glycophorin-Sepharose column. The fraction retained on the column was eluted with 0.2% sodium dodecyl sulfate. It lacked the high-molecular-weight polypeptides and was highly enriched with two polypeptides (apparent molecular weights, 45,000 and 25,000). The eluted fraction exhibited a high capacity to bind to glycophorin-Sepharose beads and a lower capacity to bind to RBC. The binding of the eluted fraction to RBC was almost completely abolished by glycophorin, but not by its hydrophobic moiety. Binding of the fraction to glycophorin-Sepharose beads was inhibited to about the same extent by both glycophorin and its hydrophobic moiety, suggesting that components of the eluted fraction are also capable of binding to the hydrophobic moiety of glycophorin, which is apparently exposed on the beads but not on the RBC surface.

Intracellular structures of Mycoplasma pneumoniae revealed after membrane removal

Mycoplasma pneumoniae was grown on Formvar- and carbon-coated electron microscope grids and treated with the nonionic detergent Triton X-100 to gently remove the membrane and cytoplasm. The detergent mixture was composed of 0.5% Triton X-100 in SSR-2 broth base. After this treatment, the grids were rinsed in a mixture of 0.1 M KCl, 5 mM MgCl2, and 6 mM potassium phosphate buffer (pH 7.05) and negatively stained with uranyl acetate. The Triton X-100-resistant remains of M. pneumoniae after gentle removal of the membrane and cytoplasm consisted of fibrous structures oriented similarly to the undisrupted cells. The thin fibers displayed a negative staining quality and diameter analogous to that of rabbit muscle F-actin. The fibrous moieties ended in rodlike condensations which appeared striated in negatively stained and shadowed preparations. These striations were regular, and the majority of rod structures had lengths of 220 to 300 nm and widths of 50 to 80 nm. Specific antibody to rabbit muscle actin, produced in guinea pigs, was used in indirect immunofluorescence of the M. pneumoniae colonies. Fluorescence was detected, with concentrations at the colony center and at the tips of filamentous cells.