Native surface association of a recombinant 38-kilodalton Treponema pallidum antigen isolated from the Escherichia coli outer membrane

LPS unmasking of Shigella flexneri reveals preferential localisation of tagged outer membrane protease IcsP to septa and new poles

The Shigella flexneri outer membrane (OM) protease IcsP (SopA) is a member of the enterobacterial Omptin family of proteases which cleaves the polarly localised OM protein IcsA that is essential for Shigella virulence. Unlike IcsA however, the specific localisation of IcsP on the cell surface is unknown. To determine the distribution of IcsP, a haemagglutinin (HA) epitope was inserted into the non-essential IcsP OM loop 5 using Splicing by Overlap Extension (SOE) PCR, and IcsP(HA) was characterised. Quantum Dot (QD) immunofluorescence (IF) surface labelling of IcsP(HA) was then undertaken. Quantitative fluorescence analysis of S. flexneri 2a 2457T treated with and without tunicaymcin to deplete lipopolysaccharide (LPS) O antigen (Oag) showed that IcsP(HA) was asymmetrically distributed on the surface of septating and non-septating cells, and that this distribution was masked by LPS Oag in untreated cells. Double QD IF labelling of IcsP(HA) and IcsA showed that IcsP(HA) preferentially localised to the new pole of non-septating cells and to the septum of septating cells. The localisation of IcsP(HA) in a rough LPS S. flexneri 2457T strain (with no Oag) was also investigated and a similar distribution of IcsP(HA) was observed. Complementation of the rough LPS strain with rmlD resulted in restored LPS Oag chain expression and loss of IcsP(HA) detection, providing further support for LPS Oag masking of surface proteins. Our data presents for the first time the distribution for the Omptin OM protease IcsP, relative to IcsA, and the effect of LPS Oag masking on its detection.

Heterologous expression of the Treponema pallidum laminin-binding adhesin Tp0751 in the culturable spirochete Treponema phagedenis

Treponema pallidum subsp. pallidum, the causative agent of syphilis, is an unculturable, genetically intractable bacterium. Here we report the use of the shuttle vector pKMR4PEMCS for the expression of a previously identified T. pallidum laminin-binding adhesin, Tp0751, in the nonadherent, culturable spirochete Treponema phagedenis. Heterologous expression of Tp0751 in T. phagedenis was confirmed via reverse transcriptase PCR analysis with tp0751 gene-specific primers and immunofluorescence analysis with Tp0751-specific antibodies; the latter assay verified the expression of the laminin-binding adhesin on the treponemal surface. Expression of Tp0751 within T. phagedenis was functionally confirmed via laminin attachment assays, in which heterologous Tp0751 expression conferred upon T. phagedenis the capacity to attach to laminin. Further, specific inhibition of the attachment of T. phagedenis heterologously expressing Tp0751 to laminin was achieved by using purified antibodies raised against recombinant T. pallidum Tp0751. This is the first report of heterologous expression of a gene from an unculturable treponeme in T. phagedenis. This novel methodology will significantly advance the field of syphilis research by allowing targeted investigations of T. pallidum proteins purported to play a role in pathogenesis, and specifically host cell attachment, in the nonadherent spirochete T. phagedenis.

Biological basis for syphilis

Syphilis is a chronic sexually transmitted disease caused by Treponema pallidum subsp. pallidum. Clinical manifestations separate the disease into stages; late stages of disease are now uncommon compared to the preantibiotic era. T. pallidum has an unusually small genome and lacks genes that encode many metabolic functions and classical virulence factors. The organism is extremely sensitive to environmental conditions and has not been continuously cultivated in vitro. Nonetheless, T. pallidum is highly infectious and survives for decades in the untreated host. Early syphilis lesions result from the host's immune response to the treponemes. Bacterial clearance and resolution of early lesions results from a delayed hypersensitivity response, although some organisms escape to cause persistent infection. One factor contributing to T. pallidum's chronicity is the paucity of integral outer membrane proteins, rendering intact organisms virtually invisible to the immune system. Antigenic variation of TprK, a putative surface-exposed protein, is likely to contribute to immune evasion. T. pallidum remains exquisitely sensitive to penicillin, but macrolide resistance has recently been identified in a number of geographic regions. The development of a syphilis vaccine, thus far elusive, would have a significant positive impact on global health.

Sequence analysis and recombinant expression of a 28-kilodalton Treponema pallidum subsp. pallidum rare outer membrane protein (Tromp2)

In this study, we report the cloning, sequencing, and expression of the gene encoding a 28-kDa Treponema pallidum subsp. pallidum rare outer membrane protein (TROMP), designated Tromp2. The tromp2 gene encodes a precursor protein of 242 amino acids including a putative signal peptide of 24 amino acids ending in a type I signal peptidase cleavage site of Leu-Ala-Ala. The mature protein of 218 amino acids has a calculated molecular weight of 24,759 and a calculated pI of 7.3. The predicted secondary structure of Tromp2 shows nine transmembrane segments of amphipathic beta-sheets typical of outer membrane proteins. Recombinant Tromp2 (rTromp2) was expressed with its native signal peptide, using a tightly regulated T7 RNA polymerase expression vector. Under high-level expression conditions, rTromp2 fractionated exclusively with the Escherichia coli outer membrane. Antiserum raised against rTromp2 was generated and used to identify native Tromp2 in cellular fractionations. Following Triton X-114 extraction and phase separation of T. pallidum, the 28-kDa Tromp2 protein was detected prominently in the detergent phase. Alkali and high-salt treatment of purified outer membrane from T. pallidum, conditions which remove peripherally associated membrane proteins, demonstrated that Tromp2 is an integral membrane protein. Whole-mount immunoelectron microscopy of E. coli cells expressing rTromp2 showed specific surface antibody binding. These findings demonstrate that Tromp2 is a membrane-spanning outer membrane protein, the second such protein to be identified for T. pallidum.

Porin activity and sequence analysis of a 31-kilodalton Treponema pallidum subsp. pallidum rare outer membrane protein (Tromp1)

We have recently reported the isolation and purification of the Treponema pallidum outer membrane and the identification of its rare protein constituents, including a 31-kDa protein markedly enriched in the outer membrane preparation (D.R. Blanco, K. Reimann, J. Skare, C.I. Champion, D. Foley, M. M. Exner, R. E. W. Hancock, J. N. Miller, and M. A. Lovett, J. Bacteriol. 176:6088-6099, 1994). In this study, we report the cloning, sequencing, and expression of the structural gene which encodes the 31-kDa outer membrane protein, designated Tromp1. The deduced amino acid sequence from the tromp1 gene sequence encodes a 318-amino-acid polypeptide with a putative 40-amino-acid signal peptide. Processing of Tromp1 results in a mature protein with a predicted molecular mass of 30,415 Da and a calculated pI of 6.6. Secondary-structure predictions identified repeated stretches of amphipathic beta-sheets typical of outer membrane protein membrane-spanning sequences. A topological model of Tromp1 containing 14 transmembrane segments is proposed. Specific antiserum against a recombinant Tromp1 fusion protein was generated and was used to identify native Tromp1 in cellular fractionation. Upon Triton X-114 extraction and phase separation of T. pallidum, the 31-kDa Tromp1 protein was detected in the detergent-phase fraction but not in the protoplasmic cylinder or aqueousphase fractions, consistent with a hydrophobic outer membrane protein. Anti-Tromp1 antiserum was also used to identify native Tromp1 purified from whole T. pallidum by Triton X-100 solubilization followed by nondenaturing isoelectric focusing. Reconstitution of purified Tromp1 into planar lipid bilayers showed porin activity based on the measured single channel conductanes of 0.15 and 0.7 nS in 1 M KCl. These findings demonstrate that Tromp1 is a transmembrane outer membrane porin protein of T. pallidum.

Treponema pallidum and the quest for outer membrane proteins

Treponema pallidum, the syphilis spirochaete, has a remarkable ability to evade the humoral and cellular responses it elicits in infected hosts. Although formerly attributed to the presence of an outer coat comprised of serum proteins and/or mucopolysaccharides, current evidence indicates that the immuno-evasiveness of this bacterium is largely the result of its unusual molecular architecture. Based upon a combination of molecular, biochemical, and ultrastructural data, it is now believed that the T. pallidum outer membrane (OM) contains a paucity of poorly immunogenic transmembrane proteins ('rare outer membrane proteins') and that its highly immunogenic proteins are lipoproteins anchored predominantly to the periplasmic leaflet of the cytoplasmic membrane. The presence in the T. pallidum OM of a limited number of transmembrane proteins has profound implications for understanding syphilis pathogenesis as well as treponemal physiology. Two major strategies for molecular characterization of rare outer membrane proteins have evolved. The first involves the identification of candidate OM proteins as fusions with Escherichia coli alkaline phosphatase. The second involves the characterization of candidate OM proteins identified in outer membranes isolated from virulent T. pallidum. Criteria to define candidate OM proteins and for definitive identification of rare OM proteins are proposed as a guide for future studies.

Treponema pallidum in gel microdroplets: a novel strategy for investigation of treponemal molecular architecture

Controversy exists regarding the constituents and antigenic properties of the Treponema pallidum outer membrane; a major point of contention concerns the cellular location(s) of the spirochaete's lipoprotein immunogens. To address these issues and circumvent problems associated with prior efforts to localize treponemal surface antigens, we developed a novel strategy for investigating T. pallidum molecular architecture. Virulent treponemes were encapsulated in porous agarose beads (gel microdroplets) and then probed in the presence or absence of Triton X-100. Intact, encapsulated treponemes were not labelled by monospecific antisera directed against four major T. pallidum lipoproteins or a candidate T. pallidum outer membrane protein (TpN50) with C-terminal sequence homology to Escherichia coli OmpA or by human or rabbit syphilitic serum. Each of these immunologic reagents, however, labelled encapsulated treponemes co-incubated with detergent. In contrast, antibodies generated against isolated T. pallidum outer membranes labelled intact organisms and the pattern of fluorescence was consistent with the distribution of rare outer membrane proteins visualized by freeze-fracture electron microscopy. In addition to providing strong evidence that the protein portions of treponemal lipoproteins are located within the periplasmic space, these studies have extended our understanding of the topographical relationships among T. pallidum cell envelope constituents. They also demonstrate the feasibility of generating antibodies against rare outer membrane proteins and detecting them on the surfaces of virulent treponemes.

Isolation of the outer membranes from Treponema pallidum and Treponema vincentii

The outer membranes from Treponema pallidum subsp. pallidum and Treponema vincentii were isolated by a novel method. Purified outer membranes from T. pallidum and T. vincentii following sucrose gradient centrifugation banded at 7 and 31% (wt/wt) sucrose, respectively. Freeze fracture electron microscopy of purified membrane vesicles from T. pallidum and T. vincentii revealed an extremely low density of protein particles; the particle density of T. pallidum was approximately six times less than that of T. vincentii. The great majority of T. vincentii lipopolysaccharide was found in the outer membrane preparation. The T. vincentii outer membrane also contained proteins of 55 and 65 kDa. 125I-penicillin V labeling demonstrated that t. pallidum penicillin-binding proteins were found exclusively with the protoplasmic cylinders and were not detectable with purified outer membrane material, indicating the absence of inner membrane contamination. Isolated T. pallidum outer membrane was devoid of the 19-kDa 4D protein and the normally abundant 47-kDa lipoprotein known to be associated with the cytoplasmic membrane; only trace amounts of the periplasmic endoflagella were detected. Proteins associated with the T. pallidum outer membrane were identified by one- and two-dimensional electrophoretic analysis using gold staining and immunoblotting. Small amounts of strongly antigenic 17- and 45-kDa proteins were detected and shown to correspond to previously identified lipoproteins which are found principally with the cytoplasmic membrane. Less antigenic proteins of 65, 31 (acidic pI), 31 (basic pI), and 28 kDa were identified. Compared with whole-organism preparations, the 65- and the more basic 31-kDa proteins were found to be highly enriched in the outer membrane preparation, indicating that they may represent the T. pallidum rare outer membrane proteins. Reconstitution of solubilized T. pallidum outer membrane into lipid bilayer membranes revealed porin activity with two estimated channel diameters of 0.35 and 0.68 nm based on the measured single-channel conductances in 1 M KCl of 0.40 and 0.76 nS, respectively.

Characterization of the low-molecular-mass proteins of virulent Treponema pallidum

We previously demonstrated that Treponema pallidum cells incubated in vitro in the presence of heat-inactivated normal rabbit serum (HINRS) synthesize, in very small quantities, several pathogen-specific, low-molecular-mass proteins that appear to be localized extracellularly. In this study, we have taken advantage of our ability to metabolically radiolabel T. pallidum cells to high specific activity to further characterize these antigens. We found that the low-molecular-mass proteins are not related to the 15- and 17-kDa detergent-phase proteins (J. D. Radolf, N. R. Chamberlain, A. Clausell, and M. V. Norgard, Infect. Immun. 56:490-498, 1988). The low-molecular-mass proteins did not incorporate 3H-labeled fatty acids and were not precipitated by rabbit immunoglobulin G (IgG) antibodies directed against glutathione S-transferase fusions to the nonlipidated 15- and 17-kDa proteins. We prepared polyclonal antisera to the low-molecular-mass proteins by immunizing two rabbits with the concentrated supernatant of T. pallidum cells. IgG antibodies present in the sera of both rabbits precipitated a 21.5-kDa protein from solubilized extracts of T. pallidum supernatant and cells. IgG antibodies in the serum of the second rabbit precipitated an additional 15.5-kDa low-molecular-mass protein only from solubilized extracts of supernatant. While investigating the effect of eliminating HINRS from the extraction medium, we observed that the low-molecular-mass proteins remained associated with treponemal cells that were incubated in the absence of HINRS. These proteins could be eluted from the cells by the addition of HINRS or rabbit serum albumin, suggesting that they are located on or near the treponemal cell surface. The 15.5- and 21.5-kDa low-molecular-mass proteins were not washed off treponemal cells with buffer containing 1 M KCl. Experiments employing selective solubilization of the T. pallidum outer membrane with 0.1% Triton X-114 and proteinase K accessibility indicated that the 15.5-kDa protein, but not the 21.5-kDa protein, is cell surface exposed.

Polypeptides of Treponema pallidum: progress toward understanding their structural, functional, and immunologic roles. Treponema Pallidum Polypeptide Research Group

Treponema pallidum subsp. pallidum, the spirochete that causes syphilis, is unusual in a number of respects, including its small genome size, inability to grow under standard in vitro culture conditions, microaerophilism, apparent paucity of outer membrane proteins, structurally complex periplasmic flagella, and ability to evade the host immune responses and cause disease over a period of years to decades. Many of these attributes are related ultimately to its protein content. Our knowledge of the activities, structure, and immunogenicity of its proteins has been expanded by the application of recombinant DNA, hybridoma, and structural fractionation techniques. The purpose of this monograph is to summarize and correlate this new information by using two-dimensional gel electrophoresis, monoclonal antibody reactivity, sequence data, and other properties as the bases of polypeptide identification. The protein profiles of the T. pallidum subspecies causing syphilis, yaws, and endemic syphilis are virtually indistinguishable but differ considerably from those of other treponemal species. Among the most abundant polypeptides are a group of lipoproteins of unknown function that appear to be important in the immune response during syphilitic infection. The periplasmic flagella of T. pallidum and other spirochetes are unique with regard to their protein content and ultrastructure, as well as their periplasmic location. They are composed of three core proteins (homologous to the other members of the eubacterial flagellin family) and a single, unrelated sheath protein; the functional significance of this arrangement is not understood at present. Although the bacterium contains the chaperonins GroEL and DnaK, these proteins are not under the control of the heat shock regulon as they are in most organisms. Studies of the immunogenicity of T. pallidum proteins indicate that many may be useful for immunodiagnosis and immunoprotection. Future goals in T. pallidum polypeptide research include continued elucidation of their structural locations and functional activities, identification and characterization of the low-abundance outer membrane proteins, further study of the immunoprotective and immunodiagnostic potential of T. pallidum proteins, and clarification of the roles of treponemal proteins in pathogenesis.

Immunoblot analysis of sera from Ethiopian cutaneous leishmaniasis by antibody class

We have determined the specificity of the classes of anti-leishmanial antibodies which are detectable in serum from patients with active cutaneous leishmaniasis. On immunoblots, differences exist in the patterns of antigen recognition by IgG, IgM, IgA and IgE antibodies present in localized cutaneous leishmaniasis (LCL) and diffuse cutaneous leishmaniasis (DCL) patient serum. Each class of antibody showed differing patterns of banding to the various molecular species of parasite antigens. There was significant variation in the specificities of the IgG antibody reactivities between individual patients. The patterns of IgM binding were generally homogeneous and restricted to antigens with M(r) greater than 40 kDa. The only class of anti-Leishmania antibodies which showed shared patterns of common antigen recognition by all of the patients studied were IgA antibodies. The reactivities of IgE antibodies encompassed two antigens of M(r) 36 and 46-48 kDa which were not recognized by any of the other isotypes. Such antibody class associated reactivity may be useful in the design of serodiagnostic assays for the detection of Leishmania infection or other infectious agents.

The outer membrane, not a coat of host proteins, limits antigenicity of virulent Treponema pallidum

Virulent Treponema pallidum reacts poorly with the specific antibodies present in human and rabbit syphilitic sera, a phenomenon often attributed to an outer coat of host serum proteins. Here we present additional evidence that the limited antigenicity of virulent organisms actually is due to a paucity of proteins in the outer membrane. Initially, we used electron microscopy to demonstrate that the outer membrane is highly susceptible to damage from physical manipulation (i.e., centrifugation and resuspension) and nonionic detergents. Organisms with disrupted outer membranes were markedly more antigenic than intact treponemes as determined by immunoelectron microscopy (IEM) with rabbit syphilitic and antiendoflagellar antisera. Data obtained with a new radioimmunoassay, designated the T. pallidum surface-specific radioimmunoassay, corroborated these IEM findings by demonstrating that the major T. pallidum immunogens are not surface exposed; the assay also was unable to detect serum proteins, including fibronectin, on the surfaces of intact organisms. Furthermore, IEM of T. pallidum on ultrathin cryosections with monospecific anti-47-kDa-immunogen antiserum confirmed the intracellular location of the 47-kDa immunogen. On the basis of these and previous findings, we proposed a new model for T. pallidum ultrastructure in which the outer membrane contains a small number of transmembrane proteins and the major membrane immunogens are anchored by lipids to the periplasmic leaflet of the cytoplasmic membrane. This unique ultrastructure explains the remarkable ability of virulent organisms to evade the humoral immune response of the T. pallidum-infected host.

Expression in Escherichia coli of the 37-kilodalton endoflagellar sheath protein of Treponema pallidum by use of the polymerase chain reaction and a T7 expression system

We previously reported the complete primary structure of the 37-kilodalton endoflagellar sheath protein (FlaA) of Treponema pallidum. However, we were unable to determine the nucleotide sequence of flaA upstream of amino acid 10. The desired nucleotide sequence was obtained by use of a strategy based upon the polymerase chain reaction and was found to contain a consensus Escherichia coli promoter, a ribosomal binding site, and a 20-amino-acid signal peptide. Expression of FlaA in E. coli was achieved by cloning polymerase chain reaction-derived constructs lacking the native T. pallidum promoter into a temperature-inducible T7 expression system. Pulse-chase and ethanol inhibition analyses of protein processing in E. coli cells and minicells, respectively, indicated that processing of the FlaA precursor was incomplete. Native and recombinant FlaA were identical as assessed by antibody reactivity and sodium dodecyl sulfate- and two-dimensional polyacrylamide gel electrophoretic mobilities. Soluble FlaA was not detected in either the cytoplasmic or the periplasmic fractions of E. coli transformants. Fractionation of E. coli cell envelopes unexpectedly revealed that FlaA precursor and FlaA were associated with both the cytoplasmic and outer membranes. This is the first report of expression in E. coli of a T. pallidum protein which could not be cloned or expressed with its native promoter. Our data also indicate that information obtained in E. coli regarding the subcellular location of cloned treponemal proteins must be cautiously extrapolated to T. pallidum.

Molecular and antigenic analysis of treponemes

The treponemes comprise the essentially non-cultivable Treponema pallidum subspecies (agents of syphilis, yaws and other human trepanematoses), the gut pathogen of pigs, T. hydysenteriae, and a group of antigenically related, cultivable species, some of which are strongly implicated in human periodontal or gastrointestinal disease. Technical developments during the last decade have made possible the molecular analysis of components of this diverse group of organisms. Polypeptides and other macromolecular components have been characterized by techniques including electron microscopy, gel electrophoresis and immunoblotting. Antigenic analysis has been greatly enhanced by the use of monoclonal antibodies. Finally, DNA cloning and genetic manipulation have enabled the detailed investigation of important antigens at a genetic, structural and functional level. We examine these developments and provide a current overview of the data now available, which is an important foundation for applications in diagnosis, therapy, and, potentially, immunization against disease.

Molecular cloning and characterization of the 15-kilodalton major immunogen of Treponema pallidum

Pathogen-specific membrane immunogens of Treponema pallidum subsp. pallidum (T. pallidum) have been identified previously by phase partitioning with the nonionic detergent Triton X-114. One of these antigens, a 15-kilodalton (kDa) polypeptide, is expressed in relatively small quantities in T. pallidum but is highly immunogenic in both human and experimental syphilis. The native T. pallidum antigen was purified to homogeneity from the mixture of Triton X-114 detergent-phase proteins by chromatofocusing. Recombinant Escherichia coli clones were selected from a T. pallidum genomic DNA library by using monoclonal antibodies specific to the 15-kDa antigen; immunoblotting and minicell analyses confirmed expression of the 15-kDa protein in the transformants. Southern hybridization with a 1.1-kilobase fragment of DNA encoding the 15-kDa-antigen gene indicated that the gene is probably present in a single copy within the genomes of both T. pallidum and T. pallidum subsp. pertenue (the agent of yaws), while it is absent from the genome of the nonpathogenic Treponema phagedenis biotype Reiter. Cell fractionation studies with Triton X-114 demonstrated that the recombinant polypeptide possesses hydrophobic properties similar to those of the native antigen and localized the cloned 15-kDa antigen to the inner membrane of E. coli. Protein processing experiments in minicells revealed that a precursor appears to be processed to the mature 15-kDa polypeptide.

Molecular characterization of the pathogen-specific, 34-kilodalton membrane immunogen of Treponema pallidum

The 34-kilodalton (kDa) antigen of Treponema pallidum subsp. pallidum (T. pallidum) is a pathogen-specific integral membrane protein. DNA sequence analysis of the cloned gene revealed an open reading frame encoding a primary product of 204 residues with a molecular mass of 22,087 daltons. Sequences that correspond to a consensus Escherichia coli promoter and a ribosome-binding site were found upstream from the AUG start codon that begins the open reading frame, suggesting that the cloned gene can use its own regulatory sequences for expression. Examination of the deduced amino acid sequence revealed the presence of a typical procaryotic leader peptide 19 amino acids long; processing results in a mature molecule with a molecular mass of 20,123 daltons. Pulse-chase experiments with E. coli minicells confirmed that the 34-kDa antigen is synthesized as a higher-molecular-weight precursor that is processed to a mature form with the electrophoretic mobility that is characteristic for this protein. The presence in the leader peptide of the sequence Phe-Ser-Ala-Cys suggested that the 34-kDa antigen is a proteolipid. Although hydropathy analysis of the deduced amino acid sequence of the mature 34-kDa antigen predicted that the molecule was primarily hydrophilic, both the native and recombinant 34-kDa molecules displayed hydrophobic biochemical behavior by fractionating into the detergent phase after extraction of intact organisms with Triton X-114. Cell fractionation experiments with E. coli showed that the 34-kDa molecule was localized in both the inner and outer membranes of the recombinant host. The combined data demonstrate that the 34-kDa antigen is an integral membrane protein that behaves in a biochemically consistent manner in both T. pallidum and E. coli.

Demonstration of rare protein in the outer membrane of Treponema pallidum subsp. pallidum by freeze-fracture analysis

The surface of Treponema pallidum subsp. pallidum (T. pallidum), the etiologic agent of syphilis, appears antigenically inert and lacks detectable protein, as judged by immunocytochemical and biochemical techniques commonly used to identify the outer membrane (OM) constituents of gram-negative bacteria. We examined T. pallidum by freeze-fracture electron microscopy to visualize the architecture of its OM. Treponema phagedenis biotype Reiter (T. phagedenis Reiter), a nonpathogenic host-associated treponeme, and Spirochaeta aurantia, a free-living spirochete, were studied similarly. Few intramembranous particles interrupted the smooth convex and concave fracture faces of the OM of T. pallidum, demonstrating that the OM of this organism is an unusual, nearly naked lipid bilayer. In contrast, the concave fracture face of the OM of S. aurantia was densely covered with particles, indicating the presence of abundant integral membrane proteins, a feature shared by typical gram-negative organisms. The concentration of particles in the OM concave fracture face of T. phagedenis Reiter was intermediate between those of T. pallidum and S. aurantia. Similar to typical gram-negative bacteria, the OM convex fracture faces of the three spirochetes contained relatively few particles. The unique molecular architecture of the OM of T. pallidum can explain the puzzling in vitro properties of the surface of the organism and may reflect a specific adaptation by which treponemes evade the host immune response.

Cloning and sequencing of a Treponema pallidum gene encoding a 31.3-kilodalton endoflagellar subunit (FlaB2)

A library of Treponema pallidum DNA was established in the direct selection vector pUN121. Six clones carrying a gene coding for a 33-kilodalton T. pallidum flagellum subunit were identified by colony hybridization with an oligodeoxynucleotide probe based on the N-terminal amino acid sequence of this subunit. An open reading frame of 286 amino acids with the expected N-terminal sequence and absence of cysteine residues was identified. The deduced protein had a calculated molecular weight of 31.3 kilodaltons. We propose to name this flagellar subunit FlaB2. FlaB2 shows a significant amino acid homology with flagellins of several remotely related bacterial species. This homology was most pronounced corresponding to the C-terminal and N-terminal parts of the protein, whereas the central region was variable.

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.

Isolation and characterization of recombinant Escherichia coli clones secreting a 24-kilodalton antigen of Treponema pallidum

Escherichia coli clones containing Treponema pallidum DNA in the pUC8 vector and secreting a 24-kilodalton antigen of T. pallidum have been isolated. Both syphilitic human and syphilis-immune rabbit sera reacted with the recombinant p24 antigen, indicating that an equivalent protein in T. pallidum is capable of eliciting antibody responses during natural infections. The p24 antigen of T. pallidum was identified by using two-dimensional gel electrophoresis and immunoblotting with monospecific anti-p24 serum. We tentatively concluded that this cloned antigen is a secreted protein or a labile or minor component of T. pallidum because (i) p24 was secreted by the recombinant E. coli cells; (ii) recombinant p24 in E. coli cells was processed into several smaller species with molecular masses ranging from 12 to 20 kilodaltons, which correlate well with the masses of secreted antigens described by others; and (iii) p24 protein appeared to be highly antigenic during natural infections, but only a very small amount of this antigen was associated with or retained by the purified organisms. The possible role of the p24 protein in determining the growth characteristics of T. pallidum is suggested by the ability of recombinant p24 to induce growth changes in E. coli cells. All E. coli colonies expressing the p24 polypeptide exhibited a flat and rough colony morphology and a filamentous growth pattern that were different from those of other E. coli cells. The DNA sequence coding for the p24 polypeptide is located on a 1.7-kilobase-pair BamHI fragment of the T. pallidum genomic DNA and is absent in the nonpathogenic Treponema phagedenis DNA. However, any possible relationship between the p24 antigen and the virulence of T. pallidum remains to be determined. In preliminary studies, rabbits immunized with the purified p24 were not protected from the infection with live T. pallidum organisms.

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.

Identification of Treponema pallidum penicillin-binding proteins

Penicillin-binding proteins of 180, 89, 80, 68, 61, 41, and 38 kilodaltons were identified in Treponema pallidum (Nichols) by their covalent binding of [35S]benzylpenicillin. Penicillin-binding proteins are localized in the plasma membranes of many bacterial species and may serve as useful markers for determining plasma membrane intactness in T. pallidum fractionation studies.

Changes in the cell surface properties of Treponema pallidum that occur during in vitro incubation of freshly extracted organisms

We previously reported that a number of Treponema pallidum membrane proteins appear to reside on the cell surface, since intact treponemes radiolabeled by overnight incubation in medium containing [35S]methionine bind immunoglobulin G (IgG) antibodies directed against these proteins. In the present study, it was found that freshly extracted organisms radiolabeled in vitro for only 2 h inefficiently bound IgG antibodies directed against just two proteins of molecular weights 40,000 and 34,000. An in vitro incubation period of greater than 8 h was required before IgG antibodies present in rabbit syphilitic serum could recognize additional protein antigens on the cell surface. Treatment of aged treponemes, but not freshly extracted organisms, with 0.04% sodium dodecyl sulfate selectively removed a membranous layer from the treponemal surface. Only three treponemal proteins were found associated with this structure, including the same 40,000- and 34,000-molecular-weight proteins mentioned above. These two proteins most likely represent endoflagellar subunits, since they were precipitated with rabbit antisera prepared against purified endoflagellar subunits of the cultivable treponemal strain Treponema phagedenis. Further evidence also was obtained that cells of T. pallidum actively secrete into their extracellular environment a unique class of low-molecular-weight proteins.

The surface of virulent Treponema pallidum: resistance to antibody binding in the absence of complement and surface association of recombinant antigen 4D

The binding of immunoglobulin G present in syphilitic immune rabbit serum, syphilitic human serum, and rabbit antiserum to purified recombinant Treponema pallidum antigen 4D by T. pallidum, Nichols strain, was studied by immunoelectron microscopy. Treponemes were incubated with antiserum under the conditions of the T. pallidum immobilization test, in which T. pallidum-specific antibody renders the organism nonmotile and avirulent only in the presence of complement after a 16-h incubation period in an anaerobic environment. Antibody was not demonstrable on the surface of T. pallidum incubated with nonimmune rabbit serum or normal human serum in the presence of complement. Similarly, in the absence of complement, little or no antibody was found on the treponemal surface after incubation with syphilitic immune rabbit serum, syphilitic human serum, or rabbit antiserum directed against the recombinant 4D antigen. The addition of complement to syphilitic immune rabbit serum, syphilitic human serum, and anti-4D antibody resulted in immobilization and the deposition of antibody on the entire surface of the immobilized organisms. These results corroborate earlier work by other investigators demonstrating the resistance of freshly isolated T. pallidum to antibody binding in a variety of serological tests. Detection of 4D antigen on the surface of immobilized T. pallidum strongly implies that the use of T. pallidum immobilization test conditions provides a means to demonstrate the association of individual surface antigens on virulent T. pallidum. The resistance of T. pallidum to antibody binding may be relevant to the pathogenesis of syphilis.