Identification of gene products of the P1 operon of Mycoplasma pneumoniae

Protein cleavage influences surface protein presentation in Mycoplasma pneumoniae

Mycoplasma pneumoniae is a significant cause of pneumonia and post infection sequelae affecting organ sites distant to the respiratory tract are common. It is also a model organism where extensive 'omics' studies have been conducted to gain insight into how minimal genome self-replicating organisms function. An N-terminome study undertaken here identified 4898 unique N-terminal peptides that mapped to 391 (56%) predicted M. pneumoniae proteins. True N-terminal sequences beginning with the initiating methionine (iMet) residue from the predicted Open Reading Frame (ORF) were identified for 163 proteins. Notably, almost half (317; 46%) of the ORFS derived from M. pneumoniae strain M129 are post-translationally modified, presumably by proteolytic processing, because dimethyl labelled neo-N-termini were characterised that mapped beyond the predicted N-terminus. An analysis of the N-terminome describes endoproteolytic processing events predominately targeting tryptic-like sites, though cleavages at negatively charged residues in P1' (D and E) with lysine or serine/alanine in P2' and P3' positions also occurred frequently. Surfaceome studies identified 160 proteins (23% of the proteome) to be exposed on the extracellular surface of M. pneumoniae. The two orthogonal methodologies used to characterise the surfaceome each identified the same 116 proteins, a 72% (116/160) overlap. Apart from lipoproteins, transporters, and adhesins, 93/160 (58%) of the surface proteins lack signal peptides and have well characterised, canonical functions in the cell. Of the 160 surface proteins identified, 134 were also targets of endo-proteolytic processing. These processing events are likely to have profound implications for how the host immune system recognises and responds to M. pneumoniae.

Immunodominant proteins P1 and P40/P90 from human pathogen Mycoplasma pneumoniae

Mycoplasma pneumoniae is a bacterial human pathogen that causes primary atypical pneumonia. M. pneumoniae motility and infectivity are mediated by the immunodominant proteins P1 and P40/P90, which form a transmembrane adhesion complex. Here we report the structure of P1, determined by X-ray crystallography and cryo-electron microscopy, and the X-ray structure of P40/P90. Contrary to what had been suggested, the binding site for sialic acid was found in P40/P90 and not in P1. Genetic and clinical variability concentrates on the N-terminal domain surfaces of P1 and P40/P90. Polyclonal antibodies generated against the mostly conserved C-terminal domain of P1 inhibited adhesion of M. pneumoniae, and serology assays with sera from infected patients were positive when tested against this C-terminal domain. P40/P90 also showed strong reactivity against human infected sera. The architectural elements determined for P1 and P40/P90 open new possibilities in vaccine development against M. pneumoniae infections.

Cell surface processing of the P1 adhesin of Mycoplasma pneumoniae identifies novel domains that bind host molecules

Mycoplasma pneumoniae is a genome reduced pathogen and causative agent of community acquired pneumonia. The major cellular adhesin, P1, localises to the tip of the attachment organelle forming a complex with P40 and P90, two cleavage fragments derived by processing Mpn142, and other molecules with adhesive and mobility functions. LC-MS/MS analysis of M. pneumoniae M129 proteins derived from whole cell lysates and eluents from affinity matrices coupled with chemically diverse host molecules identified 22 proteoforms of P1. Terminomics was used to characterise 17 cleavage events many of which were independently verified by the identification of semi-tryptic peptides in our proteome studies and by immunoblotting. One cleavage event released ¹⁵⁹⁷TSAAKPGAPRPPVPPKPGAPKPPVQPPKKPA¹⁶²⁷ from the C-terminus of P1 and this peptide was shown to bind to a range of host molecules. A smaller synthetic peptide comprising the C-terminal 15 amino acids, ¹⁶¹³PGAPKPPVQPPKKPA¹⁶²⁷, selectively bound cytoskeletal intermediate filament proteins cytokeratin 7, cytokeratin 8, cytokeratin 18, and vimentin from a native A549 cell lysate. Collectively, our data suggests that ectodomain shedding occurs on the surface of M. pneumoniae where it may alter the functional diversity of P1, Mpn142 and other surface proteins such as elongation factor Tu via a mechanism similar to that described in Mycoplasma hyopneumoniae.

Mycoplasma pneumoniae from the Respiratory Tract and Beyond

Mycoplasma pneumoniae is an important cause of respiratory tract infections in children as well as adults that can range in severity from mild to life-threatening. Over the past several years there has been much new information published concerning infections caused by this organism. New molecular-based tests for M. pneumoniae detection are now commercially available in the United States, and advances in molecular typing systems have enhanced understanding of the epidemiology of infections. More strains have had their entire genome sequences published, providing additional insights into pathogenic mechanisms. Clinically significant acquired macrolide resistance has emerged worldwide and is now complicating treatment. In vitro susceptibility testing methods have been standardized, and several new drugs that may be effective against this organism are undergoing development. This review focuses on the many new developments that have occurred over the past several years that enhance our understanding of this microbe, which is among the smallest bacterial pathogens but one of great clinical importance.

P40 and P90 from Mpn142 are Targets of Multiple Processing Events on the Surface of Mycoplasma pneumoniae

Mycoplasma pneumoniae is a significant cause of community acquired pneumonia globally. Despite having a genome less than 1 Mb in size, M. pneumoniae presents a structurally sophisticated attachment organelle that (i) provides cell polarity, (ii) directs adherence to receptors presented on respiratory epithelium, and (iii) plays a major role in cell motility. The major adhesins, P1 (Mpn141) and P30 (Mpn453), are localised to the tip of the attachment organelle by the surface accessible cleavage fragments P90 and P40 derived from Mpn142. Two events play a defining role in the formation of P90 and P40; removal of a leader peptide at position 26 (²³SLA↓NTY²⁸) during secretion to the cell surface and cleavage at amino acid 455 (⁴⁵²GPL↓RAG⁴⁵⁷) generating P40 and P90. Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS) analysis of tryptic peptides generated by digesting size-fractionated cell lysates of M. pneumoniae identified 15 cleavage fragments of Mpn142 ranging in mass from 9–84 kDa. Further evidence for the existence of cleavage fragments of Mpn142 was generated by mapping tryptic peptides to proteins recovered from size fractionated eluents from affinity columns loaded with heparin, fibronectin, fetuin, actin, plasminogen and A549 surface proteins as bait. To define the sites of cleavage in Mpn142, neo-N-termini in cell lysates of M. pneumoniae were dimethyl-labelled and characterised by LC-MS/MS. Our data suggests that Mpn142 is cleaved to generate adhesins that are auxiliary to P1 and P30.

MalF is essential for persistence of Mycoplasma gallisepticum in vivo

There is limited understanding of the molecular basis of virulence in the important avian pathogen Mycoplasma gallisepticum. To define genes that may be involved in colonization of chickens, a collection of mutants of the virulent Ap3AS strain of M. gallisepticum were generated by signature-tagged transposon mutagenesis. The collection included mutants with single insertions in the genes encoding the adhesin GapA and the cytadherence-related protein CrmA, and Western blotting confirmed that these mutants did not express these proteins. In two separate in vivo screenings, two GapA-deficient mutants (ST mutants 02-1 and 06-1) were occasionally recovered from birds, suggesting that GapA expression may not always be essential for persistence of strain Ap3AS. CrmA-deficient ST mutant 33-1 colonized birds poorly and had reduced virulence, indicating that CrmA was a significant virulence factor, but was not absolutely essential for colonization. ST mutant 04-1 contained a single transposon insertion in malF, a predicted ABC sugar transport permease, and could not be reisolated even when inoculated by itself into a group of birds, suggesting that expression of MalF was essential for persistence of M. galliseptium strain Ap3AS in infected birds.

Protein kinase/phosphatase function correlates with gliding motility in Mycoplasma pneumoniae

Mycoplasma pneumoniae exhibits a novel form of gliding motility that is mediated by the terminal organelle, a differentiated polar structure. Given that genes known to be involved in gliding in other organisms are absent in M. pneumoniae, random transposon mutagenesis was employed to generate mutants with gliding-deficient phenotypes. Transposon insertions in the only annotated Ser/Thr protein kinase gene (prkC; MPN248) and its cognate phosphatase gene (prpC; MPN247) in M. pneumoniae resulted in significant and contrasting effects on gliding frequencies. prkC mutant cells glided at approximately half the frequency of wild-type cells, while prpC mutant cells glided more than twice as frequently as wild-type cells. Phosphoprotein staining confirmed the association between phosphorylation of the cytoskeletal proteins HMW1 and HMW2 and membrane protein P1 and the gliding phenotype. When the prpC mutant was complemented by transposon delivery of a wild-type copy of the prpC allele, gliding frequencies and phosphorylation levels returned to the wild-type standard. Surprisingly, delivery of the recombinant wild-type prkC allele dramatically increased gliding frequency to a level approximately 3-fold greater than that of wild-type in the prkC mutant. Collectively, these data suggest that PrkC and PrpC work in opposition in M. pneumoniae to influence gliding frequency.

Mycoplasma pneumoniae large DNA repetitive elements RepMP1 show type specific organization among strains

Mycoplasma pneumoniae is the smallest self-replicating bacterium with a streamlined genome of 0.81 Mb. Complete genome analysis revealed the presence of multiple copies of four large repetitive elements (designated RepMP1, RepMP2/3, RepMP4 and RepMP5) that are implicated in creating sequence variations among individual strains. Recently, we described RepMP1-associated sequence variations between reference strain M129 and clinical isolate S1 that involved three RepMP1-genes (i.e. mpn130, mpn137 and mpn138). Using PCR and sequencing we analyze 28 additional M. pneumoniae strains and demonstrate the existence of S1-like sequence variants in nine strains and M129-like variants in the remaining nineteen strains. We propose a series of recombination steps that facilitates transition from M129- to S1-like sequence variants. Next we examined the remaining RepMP1-genes and observed no other rearrangements related to the repeat element. The only other detected difference was varying numbers of the 21-nucleotide tandem repeats within mpn127, mpn137, mpn501 and mpn524. Furthermore, typing of strains through analysis of large RepMPs localized within the adhesin P1 operon revealed that sequence divergence involving RepMP1-genes mpn130, mpn137 and mpn138 is strictly type-specific. Once more our analysis confirmed existence of two highly conserved groups of M. pneumoniae strains.

Microbial antigenic variation mediated by homologous DNA recombination

Pathogenic microorganisms employ numerous molecular strategies in order to delay or circumvent recognition by the immune system of their host. One of the most widely used strategies of immune evasion is antigenic variation, in which immunogenic molecules expressed on the surface of a microorganism are continuously modified. As a consequence, the host is forced to constantly adapt its humoral immune response against this pathogen. An antigenic change thus provides the microorganism with an opportunity to persist and/or replicate within the host (population) for an extended period of time or to effectively infect a previously infected host. In most cases, antigenic variation is caused by genetic processes that lead to the modification of the amino acid sequence of a particular antigen or to alterations in the expression of biosynthesis genes that induce changes in the expression of a variant antigen. Here, we will review antigenic variation systems that rely on homologous DNA recombination and that are found in a wide range of cellular, human pathogens, including bacteria (such as Neisseria spp., Borrelia spp., Treponema pallidum, and Mycoplasma spp.), fungi (such as Pneumocystis carinii) and parasites (such as the African trypanosome Trypanosoma brucei). Specifically, the various DNA recombination-based antigenic variation systems will be discussed with a focus on the employed mechanisms of recombination, the DNA substrates, and the enzymatic machinery involved.

Optimized serodiagnosis of Mycoplasma pneumoniae infections

Serologic methods are well established for the diagnosis of Mycoplasma pneumoniae infections in humans, but they are less sensitive than polymerase chain reaction (PCR). To improve their sensitivity, a new panel of antigens was tested. Compared with PCR results, up to 92% of PCR-positive patients were confirmed by our immunoblotting approach having a specificity between 92.6% and 100%.

Variation in a surface-exposed region of the Mycoplasma pneumoniae P40 protein as a consequence of homologous DNA recombination between RepMP5 elements

Mycoplasma pneumoniae is a human pathogen that causes a range of respiratory tract infections. The first step in infection is adherence of the bacteria to the respiratory epithelium. This step is mediated by a specialized organelle, which contains several proteins (cytadhesins) that have an important function in adherence. Two of these cytadhesins, P40 and P90, represent the proteolytic products from a single 130 kDa protein precursor, which is encoded by the MPN142 gene. Interestingly, MPN142 contains a repetitive DNA element, termed RepMP5, of which homologues are found at seven other loci within the M. pneumoniae genome. It has been hypothesized that these RepMP5 elements, which are similar but not identical in sequence, recombine with their counterpart within MPN142 and thereby provide a source of sequence variation for this gene. As this variation may give rise to amino acid changes within P40 and P90, the recombination between RepMP5 elements may constitute the basis of antigenic variation and, possibly, immune evasion by M. pneumoniae. To investigate the sequence variation of MPN142 in relation to inter-RepMP5 recombination, we determined the sequences of all RepMP5 elements in a collection of 25 strains. The results indicate that: (i) inter-RepMP5 recombination events have occurred in seven of the strains, and (ii) putative RepMP5 recombination events involving MPN142 have induced amino acid changes in a surface-exposed part of the P40 protein in two of the strains. We conclude that recombination between RepMP5 elements is a common phenomenon that may lead to sequence variation of MPN142-encoded proteins.

Characterisation of subtype- and variant-specific antigen regions of the P1 adhesin of Mycoplasma pneumoniae

Distinct sequence differences within the repetitive elements (RepMP) of the Mycoplasma pneumoniae P1 adhesin are the only targets to discriminate patient isolates with molecular approaches into subtypes and variants. Since the P1 protein is also one of the most immunodominant proteins of the bacterium, the antigenic regions of the differing repetitive sequences might be of epidemiological significance for the observation of time-dependent outbreaks due to defined subtypes and variants of M. pneumoniae in the human population. By establishing a set of four subtype- and variant 2-specific recombinant proteins, we investigated the antigenicity of the variable P1 protein regions with sera of subtype- and variant-specific immunised animals and sera of M. pneumoniae-positive pneumonia patients. The results of the ELISA experiments confirmed the immunogenic character of the differing parts of the P1 adhesin and the occurrence of a specific immune response of the immunised animals. The detection of subtype- and variant-specific antibodies in the investigated sera strongly support the hypothesis of a selective immune response. It might be indicative for the partial protection of the host to a defined endemic or epidemic strain and therefore also the reason for a reduced protection against secondary infections with a differing subtype and variant of M. pneumoniae strains compared to the first contact.

Mycoplasmas: a distinct cytoskeleton for wall-less bacteria

The bacterial genus Mycoplasma includes a large number of highly genomically-reduced species which in nature are associated with hosts either commensally or pathogenically. Several Mycoplasma species, including Mycoplasma pneumoniae, feature a multifunctional polar structure, the terminal organelle. Essential for colonization of the host and for gliding motility, the terminal organelle is associated with an internal cytoskeleton crucial to its assembly and function. This cytoskeleton is structurally and compositionally novel as compared with the cytoskeletons of other organisms, including other bacteria, is also involved in the cell division process. In this review we discuss the cytoskeletal structures and protein components of the attachment organelle and how they might interact and contribute to its various functions.

Synthesis, stability, and function of cytadhesin P1 and accessory protein B/C complex of Mycoplasma pneumoniae

The genes MPN141 and MPN142 encode the major adhesin P1 and the cytadherence-related B/C proteins (P90/P40), respectively, in Mycoplasma pneumoniae. Using reverse transcriptase PCR we found open reading frames MPN140 to MPN142 constitute a polycistronic transcriptional unit. Cytadherence mutant IV-22 has a frameshift mutation in MPN141 and lacks the P1, B, or C proteins. Recombinant MPN141 and/or MPN142 were introduced into mutant IV-22 by transposon delivery in several configurations, and the levels of the P1, B, and C proteins were assessed by immunoblotting. MPN142 in mutant IV-22 has a wild-type nucleotide sequence, yet the introduction of recombinant MPN141 alone to mutant IV-22, although it restored P1 levels, failed to restore levels of B or C. In contrast, recombinant MPN141 and MPN142 delivered in cis or in trans were sufficient to restore all three proteins. Taken together, our data indicated that some but not all synthesis of B or C is dependent on coupling to the translation of P1 immediately upstream of MPN142 and demonstrated that proteins B and C are not stable in the absence of P1. The linkage of MPN141 and MPN142 at the levels of transcription, translation, and protein stability, in addition to their previously demonstrated colocalization and the requirement of B and/or C for P1 function, reinforces the conclusion that these proteins constitute a multiprotein complex that functions in receptor binding.

In vivo expression analysis of the P97 and P102 paralog families of Mycoplasma hyopneumoniae

The P97 adhesin and P102 genes of Mycoplasma hyopneumoniae each have six paralogs in the genome. We tested whether these genes were expressed during infection. P102 is associated with the mycoplasma and with swine cilia. Further, most of the paralogs were transcribed in vivo in two gene transcriptional units.

Experimental proof for a signal peptidase I like activity in Mycoplasma pneumoniae, but absence of a gene encoding a conserved bacterial type I SPase

Although the annotation of the complete genome sequence of Mycoplasma pneumoniae did not reveal a bacterial type I signal peptidase (SPase I) we showed experimentally that such an activity must exist in this bacterium, by determining the N-terminus of the N-terminal gene product P40 of MPN142, formerly called ORF6 gene. Combining mass spectrometry with a method for sulfonating specifically the free amino terminal group of proteins, the cleavage site for a typical signal peptide was located between amino acids 25 and 26 of the P40 precursor protein. The experimental results were in agreement with the cleavage site predicted by computational methods providing experimental confirmation for these theoretical analyses.

Identification and complementation of a mutation associated with loss of Mycoplasma pneumoniae virulence-specific proteins B and C

A mutation in gene MPN142 (orf6) was identified in the Mycoplasma pneumoniae cytadherence mutant III-4. MPN142 encodes virulence-specific proteins P90 and P40 (proteins B and C, respectively). Analysis of MPN142 in a cytadhering revertant and complementation using a recombinant wild-type allele confirmed the role of this mutation in the cytadherence defect.

Characterization of a Mycoplasma pneumoniae hmw3 mutant: implications for attachment organelle assembly

The proteins required for adherence of the pathogen Mycoplasma pneumoniae to host respiratory epithelial cells are localized to a polar structure, the attachment organelle. A number of these proteins have been characterized functionally by analysis of noncytadhering mutants, and many are components of the mycoplasma cytoskeleton. Mutations in some cytadherence-associated proteins have pleiotropic effects, including decreased stability of other proteins, loss of adherence and motility, and abnormal morphology. The function of protein HMW3, a component of the attachment organelle, has been difficult to discern due to lack of an appropriate mutant. In this paper, we report that loss of HMW3 resulted in decreased levels and more diffuse localization of cytoskeletal protein P65, subtle changes in morphology, inability to cluster the adhesin P1 consistently at the terminal organelle, reduced cytadherence, and, in some cells, an atypical electron-dense core in the attachment organelle. This phenotype suggests a role for HMW3 in the architecture and stability of the attachment organelle.

Defining the mycoplasma 'cytoskeleton': the protein composition of the Triton X-100 insoluble fraction of the bacterium Mycoplasma pneumoniae determined by 2-D gel electrophoresis and mass spectrometry

After treating Mycoplasma pneumoniae cells with the nonionic detergent Triton X-100, an undefined, structured protein complex remains that is called the 'Triton X-100 insoluble fraction' or 'Triton shell'. By analogy with eukaryotic cells and supported by ultrastructural analyses it is supposed that this fraction contains the components of a bacterial cytoskeleton-like structure. In this study, the composition of the Triton X-100 insoluble fraction was defined by electron microscopic screening for possible structural elements, and by two-dimensional (2-D) gel electrophoresis and MS to identify the proteins present. Silver staining of 2-D gels revealed about 100 protein spots. By staining with colloidal Coomassie blue, about 50 protein spots were visualized, of which 41 were identified by determining the mass and partial sequence of tryptic peptides of individual proteins. The identified proteins belonged to several functional categories, mainly energy metabolism, translation and heat-shock response. In addition, lipoproteins were found and most of the proteins involved in cytadherence that were previously shown to be components of the Triton X-100 insoluble fraction. There were also 11 functionally unassigned proteins. Based on sequence-derived predictions, some of these might be potential candidates for structural components. Quantitatively, the most prevalent proteins were the heat-shock protein DnaK, elongation factor Tu and subunits alpha and beta of the pyruvate dehydrogenase complex (PdhA, PdhB), but definite conclusions regarding the composition of the observed structures can only be drawn after specific proteins are assigned to them, for example by immunocytochemistry.

Identification and expression of a Mycoplasma gallisepticum surface antigen recognized by a monoclonal antibody capable of inhibiting both growth and metabolism

In order to identify antigenic proteins of Mycoplasma gallisepticum, monoclonal antibodies (MAbs) against virulent M. gallisepticum R strain were produced in mice. MAb 35A6 was selected for its abilities to inhibit both growth and metabolism of M. gallisepticum in vitro. The MAb recognized a membrane protein with an apparent molecular mass of 120 kDa. The corresponding gene, designated the mgc3 gene, was cloned from an M. gallisepticum genomic DNA expression library and sequenced. The mgc3 gene is a homologue of the ORF6 gene encoding 130-kDa protein in the P1 operon of M. pneumoniae and is localized downstream of the mgc1 gene, a homologue of the P1 gene. To assess the characteristics of MGC3 protein, all 10 TGA codons in the mgc3 gene, which encode a tryptophan in the Mycoplasma species, were replaced with TGG codons, and recombinant fowlpox viruses (FPV) harboring the altered mgc3 gene were constructed. One of the recombinant FPVs was improved to express MGC3 protein on the cell surface in which the signal peptide of MGC3 protein was replaced with one from Marek's disease virus gB. These results should provide the impetus to develop a vaccine based on MGC3 protein which can induce antibodies with both growth inhibition and metabolic-inhibition activities using a recombinant FPV.

Proteins complexed to the P1 adhesin of Mycoplasma pneumoniae

Adherence of Mycoplasma pneumoniae to host cells requires several mycoplasmal membrane proteins and cytoskeleton-like proteins in addition to the adhesin P1, a transmembrane protein of 170 kDa. To analyse interactions of the P1 adhesin with other membrane proteins or with cytoskeleton-like proteins, cross-linking studies were performed in vivo using the permeant reagent paraformaldehyde. The cross-linked protein complex was isolated by immunoaffinity chromatography, and proteins complexed to the P1 protein were identified by immunoblot analysis followed by high mass accuracy tryptic peptide mapping using matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). In addition to the P1 protein and a truncated form of the same protein, the adhesin-related 30 kDa protein, two membrane proteins of 40 and 90 kDa, the cytoskeleton-associated 65 kDa protein and two cytoskeleton-forming proteins, HMW1 and HMW3, were found to be components of the isolated protein complex. Furthermore, the cross-linked complex contained the chaperone DnaK and the E1alpha subunit of pyruvate dehydrogenase. In summary, it was shown that cytadherence-associated membrane proteins are located in close proximity to cytoskeleton-like proteins, suggesting a functional interaction between membrane and cytoskeleton-like proteins. DnaK might be involved in translocation of proteins from the cytoplasm to the membrane and pyruvate dehydrogenase might be a structural protein of the attachment organelle.

Quantitative immunohistochemical analysis of the glutathione S-transferase GSTM1: in situ phenotyping in archival material

1. GSTM1 is present in only approximately 50% of Caucasian individuals and deficiency of GSTM1 is associated with susceptibility to a growing number of diseases, especially cancer. Thus, a method that would allow accurate, retrospective determination of the GSTM1 phenotype in different patient populations would have many applications. 2. Developed, therefore, is a quantitative, image-analysis-based immunohistochemical technique for the analysis of GSTM1 protein in paraffin-embedded tissue samples. It was applied to the determination of the GSTM1 phenotype using liver biopsies taken from 70 patients. 3. Of the 70 cases (depending on the cut-off point), 51-54% were deficient in GSTM1. A single 27 kD band characteristic for GSTM1 was found in seven of 16 cases analysed by Western blotting using the same GSTM1 antibody as in the immunohistochemical analysis. There was a good correlation (r = 0.87) between the staining intensity of the GSTM1 band and the staining intensity evaluated by immunohistochemistry. 4. It is concluded that this quantitative immunohistochemical method permits accurate determination of the GSTM1 phenotype and is well suited for retrospective analysis of GSTM1 expression in specific tissues in situ.

The 40- and 90-kDa membrane proteins (ORF6 gene product) of Mycoplasma pneumoniae are responsible for the tip structure formation and P1 (adhesin) association with the Triton shell

After Triton X-100 treatment of Mycoplasma pneumoniae cells, a portion of the adhesin P1 (transmembrane protein) proved to remain tightly associated with the Triton insoluble material (Triton shell) as shown previously by several authors. However, the spontaneous loss of two cytadherence-associated membrane proteins of 90 and 40 kDa (gene product of the open reading frame 6 of the P1 operon) in a hemadsorption-negative mutant, designated M5, resulted in a 100% release of the P1 protein into the Triton phase and in the lack of the characteristic tip-like attachment organelle of M. pneumoniae indicating an essential role of the open reading frame 6 gene product in tip structure formation.

Loss of HMW1 and HMW3 in noncytadhering mutants of Mycoplasma pneumoniae occurs post-translationally

The genomic sequence of Mycoplasma pneumoniae establish this cell-wall-less prokaryote as among the smallest known microorganisms capable of self-replication. However, this genomic simplicity and corresponding biosynthetic austerity are sharply contrasted by the complex terminal structure found in this species. This tip structure (attachment organelle) directs colonization of the human respiratory mucosa, leading to bronchitis and atypical pneumonia. Furthermore, formation of a second tip structure appears to precede cell division, implying temporal regulation. However, the organization, regulation, and assembly of the attachment organelle in M. pneumoniae are poorly understood, and no counterparts have been identified among the walled bacteria. M. pneumoniae possesses a cytoskeleton-like structure required to localize adhesin proteins to the attachment organelle. The cytadherence-associated proteins HMW1, HMW2, and HMW3 are components of the mycoplasma cytoskeleton, with HMW1 localizing strictly along the filamentous extensions from the cell body and HMW3 being a key structural element of the terminal organelle. Disruptions in hmw2 result in the loss of HMW1 and HMW3. However, the hmw1 and hmw3 genes were transcribed and translated at wild-type levels in hmw2 mutants. HMW1 and HMW3 were relatively stable in the wild-type background over 8 h but disappeared in the mutants over this time period. Evaluation of recombinant HMW1 levels in mycoplasma mutants suggested a requirement for the C-terminal domain of HMW1 for turnover. Finally, an apparent defect in the processing of the precursor for the adhesin protein P1 was noted in the HMW- mutants.

The adhesin related 30-kDa protein of Mycoplasma pneumoniae exhibits size and antigen variability

Mycoplasma pneumoniae is a pathogenic bacterium colonizing epithelial cells of the human respirator tract. Using an erythrocyte binding assay we isolated a cytadsorption negative mutant designated M7 which has lost 12 of a total of 13 repetitive sequences of a proline rich C-terminal region of the adhesin related 30-kDa protein. The truncated adhesin related protein of 22 kDa showed reduced antigenicity compared to the corresponding wild-type protein. Moreover, the mutant M7 proved incapable of adhering to erythrocytes and to a human colon carcinoma cell line indicating that the repetitive C-terminal region of the 30-kDa protein is essential for effective cytadherence. The adhesin related 30-kDa protein as well as the truncated forms of the corresponding protein were accessible to carboxypeptidase Y which clearly shows surface exposure of the C-terminus of this protein.

Transposon mutagenesis reinforces the correlation between Mycoplasma pneumoniae cytoskeletal protein HMW2 and cytadherence

A new genetic locus associated with Mycoplasma pneumoniae cytadherence was previously identified by transposon mutagenesis with Tn4001. This locus maps approximately 160 kbp from the genes encoding cytadherence-associated proteins HMW1 and HMW3, and yet insertions therein result in loss of these proteins and a hemadsorption-negative (HA-) phenotype, prompting the designation cytadherence-regulatory locus (crl). In the current study, passage of transformants in the absence of antibiotic selection resulted in loss of the transposon, a wild-type protein profile, and a HA+ phenotype, underscoring the correlation between crl and M. pneumoniae cytadherence. Nucleotide sequence analysis of crl revealed open reading frames (ORFs) orfp65, orfp216, orfp41, and orfp24, arranged in tandem and flanked by a promoter-like and a terminator-like sequence, suggesting a single transcriptional unit, the P65 operon. The 5' end of orfp65 mRNA was mapped by primer extension, and a likely promoter was identified just upstream. The product of each ORF was identified by using antisera prepared against fusion proteins. The previously characterized surface protein P65 is encoded by orfp65, while the 190,000 Mr cytadherence-associated protein HMW2 is a product of orfp216. Proteins with sizes of 47,000 and 41,000 Mr and unknown function were identified for orfp41 and orfp24, respectively. Structural analyses of HMW2 predict a periodicity highly characteristic of a coiled-coil conformation and five leucine zipper motifs, indicating that HMW2 probably forms dimers in vivo, which is consistent with a structural role in cytadherence. Each transposon insertion mapped to orfp216 but affected the levels of all products of the P65 operon. HMW2 is thought to form a disulfide-linked dimer, formerly designated HMW5, and examination of an hmw2 deletion mutant confirms that HMW5 is a product of the hmw2 gene.

Biofunctional domains of the Mycoplasma pneumoniae P30 adhesin

The P30 adhesin genes of spontaneous, hemadsorption-negative (HA-) class II Mycoplasma pneumoniae mutants that displayed P30 adhesin-deficient protein profiles were analyzed. One subclass of P30-deficient mutants possessed the entire p3O structural gene without alterations (825 nucleotides, encoding 275 amino acids with a predicted molecular mass of 29,743 Da [S. F. Dallo, A. Chavoya, and J. B. Baseman, Infect. Immun. 58:4163-4165, 1990]). However, the second mutant subclass contained a deletion in p3O resulting in the expression of a 25-kDa peptide (681 nucleotides, encoding 227 amino acids with a calculated molecular mass of 24,823 Da). This P25-truncated peptide lacked 8 of the 13 proline-rich amino acid repeat sequences at the carboxy terminus. Whole-cell radioimmunoprecipitation of M. pneumoniae with antibodies directed against the proline-rich repeat sequences located in the carboxy terminus demonstrated their surface accessibility. In contrast, antibodies generated against N-terminal amino acid sequences upstream of the repeats did not bind to intact mycoplasmas. The amino acid sequence homologies exhibited by the P30 adhesin and eucaryotic structural proteins were corroborated by cross-reactive epitopes shared between the P30 adhesin and fibrinogen, keratin, and myosin. These data reinforce the importance of the P30 protein in cytadherence and virulence and provide a molecular basis for postinfectious autoimmunity associated with M. pneumoniae-mediated pathologies.

Mycoplasma pneumoniae cytadherence: unravelling the tie that binds

Mycoplasma pneumoniae is the leading cause of pneumonia in older children and young adults. Mycoplasma adherence to the respiratory epithelium (cytadherence) is required for colonization and pathogenesis. Although considered to be among the smallest and simplest known prokaryotes, this cell-wall-less bacterium possesses a highly differentiated terminal structure that is thought to be functional in mycoplasma cell division, gliding motility, and cytadherence. Mutant analysis has identified mycoplasma proteins associated with cytadherence, and revealed novel regulatory features. Ultrastructural and biochemical studies have established the subcellular location and interaction of key components, several of which are phosphorylated by ATP-dependent kinase(s) in a manner that is responsive to changing nutritional conditions. This review summarizes recent progress in defining the composition, organization and regulation of the attachment organelle. What emerges is a picture of M. pneumoniae cytadherence as a multifactorial process that extends well beyond adhesin-receptor recognition.

The proline-rich P65 protein of Mycoplasma pneumoniae is a component of the Triton X-100-insoluble fraction and exhibits size polymorphism in the strains M129 and FH

Previously, we described the identification of a novel Mycoplasma pneumoniae M129 protein, named P65 because of its apparent molecular mass of 65 kDa estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (T. Proft and R. Herrmann, Mol. Microbiol. 13:337-348, 1994). DNA sequence analysis of the P65 open reading frame (orfp65), however, revealed an ORF encoding a protein with a molecular weight of 47,034. This discrepancy can be explained by the unusual amino acid composition of this protein. According to the deduced amino acid sequence, the N-terminal half of P65 contains several penta- and hexapeptides (DPNAY and DPNQAY) forming a proline-rich acidic domain. Secondary-structure predictions indicated beta-sheets and turns within that region, suggesting an extended and rigid conformation. Near the C terminus of P65 the tripeptide Arg-Gly-Asp (RGD) was found. This motif is known to play an important role in binding of extracellular matrix proteins to integrins. P65 could be located exclusively to the Triton X-100-insoluble cell fraction. The results of immunofluorescence microscopy and of immunoadsorption experiments indicated that P65 carries surface-exposed regions. Mild treatment of whole cells with proteases resulted in cleavage of a limited amount of P65 molecules, suggesting either that only a small percentage of P65 molecules are exposed on the surface or that protease cleavage is hampered by a compact protein conformation or by binding of an unknown component to P65. P65 exhibits size polymorphism in M. pneumoniae M129 and FH. This is caused by an intragenetic duplication of a 54-bp sequence within the FH orfp65. As a consequence, the number of DPNAY pentapeptides increased from 9 to 12 repeats in the FH strain.

A spontaneous hemadsorption-negative mutant of Mycoplasma pneumoniae exhibits a truncated adhesin-related 30-kilodalton protein and lacks the cytadherence-accessory protein HMW1

A spontaneous, hemadsorption-negative mutant of Mycoplasma pneumoniae lacks the cytoskeleton-forming HMW1 protein and exhibits a truncated adhesin-related 30-kDa protein. Genetic analyses revealed deletion of one nucleotide in the hmw1 gene and loss of eight repeated sequences comprising 144 nucleotides in the gene for the adhesin-related 30-kDa protein.

Sequence divergence in the ORF6 gene of Mycoplasma pneumonia

The ORF6 gene product of Mycoplasma pneumoniae is involved in a yet-unknown manner in the adhesion of the bacterium to its host cell. Part of the ORF6 gene is a repetitive DNA sequence (RepMP5), about 1,900 bp long. Seven additional similar copies of RepMP5 are dispersed on the genome. In the independently isolated strains M. pneumoniae M129 and FH, the RepMP5 copies residing in the ORF6 gene are not identical. Two conserved regions, ranging from nucleotides 1 to 799 and from nucleotide 1795 to the end of the gene, border a variable region, ranging from nucleotides 800 to 1794. This variable region differs in DNA sequence and by 201 bp. Analysis of RepMP5 copies outside the ORF6 gene showed that both M. pneumoniae M129 and M. pneumoniae FH carry a RepMP5 copy on a 6-kbp EcoRI fragment which has the same DNA sequence as the variable region of RepMP5 in the M. pneumoniae FH ORF6 gene. According to these data, a switch from the M. pneumoniae M129 ORF6 gene to the M. pneumoniae FH ORF6 gene could take place by gene conversion.

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.

Protection of immunized and previously infected chimpanzees challenged with Mycoplasma pneumoniae

Following immunization, peak geometric mean serum metabolism inhibition antibody (MIT) titres were 1:13 and 1:16 for groups of three chimpanzees each that received either the formalin-inactivated OSU-1A or experimental acellular extract vaccine, respectively. Following challenge, the mean titres for chimpanzees given the acellular vaccine peaked at 1:256 in 4 weeks and was 1:48 at 10 weeks. Chimpanzees given the OSU-1A vaccine peaked at 1:80 in 4 weeks and remained at 1:80 at 10 weeks. There was no direct correlation between the serum MIT response and the severity of disease or colonization, and thus the MIT response was not a reliable measurement of protection. The two non-immunized chimpanzees showed significant signs of disease, including cough, pharyngitis, rhinitis, fever and abnormal X-ray findings, for about 5 weeks. The chimpanzees immunized with either vaccine were less colonized and showed far less disease than non-immunized controls. Protection afforded the chimpanzees was similar to that of vaccinees in the human clinical trial given the same OSU-1A vaccine (Wenzel et al., 1977). The two previously infected chimpanzees were most protected against colonization and disease on challenge.

Immunoblot analyses of chimpanzee sera after infection and after immunization and challenge with Mycoplasma pneumoniae

Consecutive weekly or biweekly serum specimens obtained during a 3- or 4-month study from 16 chimpanzees were examined by immunoblot analyses to identify the immunogenic components of Mycoplasma pneumoniae. Six experimentally infected chimpanzees showed significant signs of overt disease, including cough, pharyngitis, rhinitis, fever, and loss of appetite. The sera of these infected chimpanzees recognized from 17 to 20 protein bands. Two control chimpanzees that were not inoculated were included in the study. Three chimpanzees immunized with a formalin-inactivated OSU-1A vaccine and three chimpanzees immunized with an experimental acellular vaccine showed minimal signs of disease on challenge. After challenge, the serum immunoblot responses of the immunized chimpanzees were similar to those of the infected chimpanzees. Before challenge, the sera of two previously infected chimpanzees recognized protein bands of 169 (which comigrated with the P1 adhesin), 148, 130, 117, 86, 61, 44, 35, 30, and 29 kDa. After challenge, the previously infected chimpanzees showed the most intense serum immunoblot responses and were most protected against colonization and disease. The sera from each of the 16 chimpanzees examined recognized a large number of immunogenic components, and the serum immunoblot responses were virtually identical to those of patients. Sera from each chimpanzee and patient recognized 169-, 148-, 130-, 117-, 86-, 44-, and 35-kDa bands and many of them recognized 67-, 63-, 61-, 56-, 32-, 30-, and 29-kDa protein bands.

Spatial arrangement of gene products of the P1 operon in the membrane of Mycoplasma pneumoniae

The spatial arrangement of three P1 operon-encoded proteins--attachment protein P1 (ORF5 gene product) and the ORF6-derived proteins of 40 and 90 kDa--in the membrane of Mycoplasma pneumoniae M129 was investigated by nearest-neighbor analysis. For these studies, the homobivalent, thiol-cleavable, and nonmembrane-permeating cross-linking reagent 3,3'-dithiobis(sulfosuccinimidylpropionate) (DTSSP) was used. The cross-linked proteins were isolated by immunoprecipitation with antibodies directed against fusion proteins of selected regions of the 40-kDa, the 90-kDa, or the P1 protein. The individual components of the immunoprecipitated protein complexes were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, autoradiography, and immunoblot analysis. This study showed that the P1 protein, the ORF6 gene product, and an unidentified 30-kDa protein were linked to each other in the intact bacterial membrane by the reagent DTSSP, indicating that these proteins are located at a maximal distance of 12 A (1 A = 0.1 nm) on the tip structure of M. pneumoniae.

The immunodominant 90-kilodalton protein is localized on the terminal tip structure of Mycoplasma pneumoniae

Immunoblot analysis of convalescent-phase sera of experimentally infected chimpanzees or monoclonal antibodies (MAbs) specific to the 90- and 40-kDa proteins of Mycoplasma pneumoniae indicated that both proteins were present in cytadsorbing, pathogenic strains PI-1428, M129, and FH but absent in noncytadsorbing, nonpathogenic strain M129-B176. Adsorption of convalescent-phase chimpanzee sera with virulent strain PI-1428 removed reactivity, whereas adsorption with avirulent strain M129-B176 did not remove reactivity to these two proteins. By using proteolysis and specific MAbs, we demonstrated that the 90- and 40-kDa proteins were surface exposed. Immunoelectron microscopy employing specific MAbs showed that the 90-kDa protein is localized on the terminal tip attachment apparatus. However, the MAb specific for the 40-kDa protein failed to indicate a similar localization. Nevertheless, these data, taken together, indicate that the immunodominant 90- and 40-kDa proteins are surface exposed, are localized on the terminal tip apparatus, and might be involved in the attachment mechanism.

The ORF6 gene product of the P1 operon of Mycoplasma pneumoniae

The P1 attachment protein gene of Mycoplasma pneumoniae is flanked by two open reading frames with a coding capacity for two proteins of 28 kDa (ORF4) and 130 kDa (ORF6), respectively. An operon-like organization in the order ORF4-P1-ORF6 was proposed by Inamine et al. (11). Instead of an expected 130 kDa protein, two proteins of 40 and 90 kDa were identified as the gene product of ORF6 which might arise from cotranslational cleavage (18). After purification of both proteins, the N-terminal amino acid of the 90 kDa protein was determined. Thus, we identified the putative cotranslational cleavage site before amino acid position 455 (R) (15). Biochemical and immunological studies indicate that both proteins are membrane-associated, exhibiting surface-exposed regions (15). Since a wild-type-derived mutant lacking the 40 as well as the 90 kDa protein shows reduced attachment to host cells we suggest that the ORF6 encodes for two proteins which contribute to proper adherence of M. pneumoniae to host cells.

Localization and biochemical characterization of the ORF6 gene product of the Mycoplasma pneumoniae P1 operon

ORF6 represents one of the two open reading frames flanking the P1 attachment protein gene of Mycoplasma pneumoniae in the order ORF4-P1-ORF6 (J.M. Inamine, T.P. Denny, S. Loechel, U. Schaper, C.H. Huang, K.F. Bott, and P.C. Hu, Gene 64:217-219, 1988; J.M. Inamine, S. Loechel, and P.C. Hu, Gene 73:175-183, 1988; C.J. Su, V.V. Tryon, and J.B. Baseman, Infect. Immun. 55:3023-3029, 1987), indicating an operonlike organization. As described previously, we identified two proteins with molecular masses of 40 and 90 kDa (B. Sperker, P.C. Hu, and R. Herrmann, Mol. Microbiol. 5:299-306, 1991) which might represent two cotranslational cleavage fragments of the ORF6 gene product. To determine the site of the putative cotranslational cleavage, the first 10 amino acids of the N terminus of the isolated 90-kDa protein were sequenced. The data are consistent with the DNA-deduced amino acid sequence between amino acid positions 455 and 465 (RAGNSSETDAL). Thus, the cleavage site was identified at amino acid position 455 (R). In this study, the two proteins were localized and biochemically characterized. Both proteins are part of the insoluble fraction of M. pneumoniae as shown by immunoblots of supernatants and pellets of mechanically disrupted cells subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Surface proteolysis followed by SDS-PAGE and Western blot (immunoblot) analysis, covalent labelling of surface-exposed proteins with [125I]iodide and subsequent immunoprecipitation of both radiolabelled proteins, immunofluorescence studies with formalized and living M. pneumoniae, and immunoadsorption experiments provided strong evidence that the 40- and 90-kDa proteins are membrane-associated proteins expressing surface-exposed regions.

Relationship between an 85 kDa protein and the protective effects of Mycoplasma pneumoniae

In the immunoblot analysis, sera from patients infected with Mycoplasma pneumoniae reacted with the 168 kDa (P1) and the 85 kDa proteins of virulent strain FH-P24 and P24-S1 mutant strain but not with the 85 kDa protein of P24-S11. Sera of hamsters and BALB/c mice, which had been immunized with live vaccines, were tested. In FH-P24 immunized animals, 100% or 80%, and in P24-S1, 40% of hamsters and 60% of BALB/c mice, developed antibodies against the 85 kDa protein, but antibodies were not detected in sera of P24-S11 immunized animals. The correlation between the development of antibodies to 85 kDa protein in the sera of vaccinated animals and the effects of protection by living vaccines were suggested.