M proteins of group A streptococci

Bacterial Binding, Phagocytosis, and Killing Capacity: Measurements Using Colony Forming Units

Herein, we provide a colony forming unit (CFU)-based counting method for quantitating the bacterial binding, phagocytosis, and killing capacity of phagocytes. Although these functions can be measured by immunofluorescence- and dye-based assays, quantitating CFUs are comparatively inexpensive and easy to perform. The protocol described below is easily modified for use with different phagocytes (e.g., macrophages, neutrophils, cell lines), types of bacteria, or opsonic conditions.

Novel Models of Streptococcus canis Colonization and Disease Reveal Modest Contributions of M-Like (SCM) Protein

Streptococcus canis is a common colonizing bacterium of the urogenital tract of cats and dogs that can also cause invasive disease in these animal populations and in humans. Although the virulence mechanisms of S. canis are not well-characterized, an M-like protein, SCM, has recently identified been as a potential virulence factor. SCM is a surface-associated protein that binds to host plasminogen and IgGs suggesting its possible importance in host-pathogen interactions. In this study, we developed in vitro and ex vivo blood component models and murine models of S. canis vaginal colonization, systemic infection, and dermal infection to compare the virulence potential of the zoonotic S. canis vaginal isolate G361 and its isogenic SCM-deficient mutant (G361∆scm). We found that while S. canis establishes vaginal colonization and causes invasive disease in vivo, the contribution of the SCM protein to virulence phenotypes in these models is modest. We conclude that SCM is dispensable for invasive disease in murine models and for resistance to human blood components ex vivo, but may contribute to mucosal persistence, highlighting a potential contribution to the recently appreciated genetic diversity of SCM across strains and hosts.

Vaccine Approaches To Protect against Group A Streptococcal Pharyngitis

Streptococcal pharyngitis (or strep throat) is a common childhood disease affecting millions of children each year, but it is one of the only childhood diseases for which a vaccine does not exist. While for decades the development of a vaccine has been the center of attention in many laboratories worldwide, with some successes, no corporate development has yet to be initiated. The reason for this probably lies in our inability to conclusively identify the streptococcal molecule or molecules responsible for the heart cross-reactive antibodies observed in the serum of rheumatic fever patients. Without this specific knowledge, any streptococcal vaccine antigen is suspect and thus not the target for a billion-dollar investment, despite the fact that the exact role of cross-reactive antibodies in rheumatic fever is still questionable. This article will describe the development of several approaches to protect against Streptococcus pyogenes infections over the past several decades.

Primary structure of streptococcal Pep M5 protein: Absence of extensive sequence repeats

Extensive sequence repeats have been observed in a biologically active fragment of type 24 streptococcal M protein, namely Pep M24 [Beachey, E. H., Sayer, J. M. & Kang, A. H. (1978) Proc. Natl. Acad. Sci. USA 75, 3163-3167]. To determine whether such extensive repetition in sequence is a common characteristic of the antiphagocytic streptococcal M proteins, we have determined the sequences of the clostripain peptides of Pep M5, a biologically active fragment of the type 5 M protein that is analogous to Pep M24. These sequences, together with the amino-terminal sequence of the whole molecule, accounted for nearly two thirds of the Pep M5 molecule. However, extensive identical repeats of the kind observed in Pep M24 were not present in Pep M5. Preliminary study of the amino acid sequence analysis of the M protein from type 6 Streptococcus has also indicated the absence of sequence repeats within the regions of this molecule examined so far. These results suggest that extensive sequence repeats may not be a common characteristic of M-protein molecules. On the other hand, the seven-residue periodicity of the nonpolar residues, a characteristic of alpha-helical coiled-coil structures, appeared to extend over most of the Pep M5 molecule. This feature has been observed previously for the partial sequences of three M protein serotypes. Thus, the important element of the M-protein structure appears to be the seven-residue periodicity necessary for the maintenance of the coiled-coil structure rather than extensive identical amino acid sequence repeats.

Infection and glomerulonephritis

Glomerular injury, occurring either as primary glomerular disease or as part of a systemic disease process, is usually a result of immune-mediated mechanisms. The morphologic reaction pattern has a diverse spectrum of appearance, ranging from normal by light microscopy in minimal change disease to crescentic forms of glomerulonephritis, with conspicuous disruption of the normal glomerular morphology. The mechanisms of glomerular immune deposit formation include trapping of circulating antigen-antibody complexes and the in situ formation of immune complexes within the glomerulus. While the majority of postinfectious immune-complex-mediated glomerulonephritides are believed to result from the deposition of circulating antigen-antibody complexes, preformed outside of the kidney and secondarily deposited in the kidney, the notion of forming in situ antigen-antibody complexes to either planted antigens or to integral structural components of the glomerulus, through "cross-reacting" autoimmune reactions, is gaining popularity in a variety of forms of glomerulonephritides. Patients with HIV infection may develop a spectrum of renal pathology, the glomerular manifestations of which include both antigen-antibody complex and nonimmune-complex-mediated pathogenetic mechanisms. Similarly, patients with Streptococcal infections, Hepatitis B virus, or Hepatitis C virus infection may develop a spectrum of glomerulonephritides, which are predominantly immune-complex-mediated. Therapy for glomerular diseases due to HIV, hepatitis B, or C virus infections remains a challenge.

Advances in potential M-protein peptide-based vaccines for preventing rheumatic fever and rheumatic heart disease

Rheumatic fever (RF) and rheumatic heart disease (RHD) are postinfectious complications of an infection (or repeated infection) with the Gram-positive bacterium, Streptococcus pyogenes (also known as group A streptococcus, GAS). RF and RHD are global problems and affect many indigenous populations of developed countries and many developing countries. However, RF and RHD are only part of a larger spectrum of diseases caused by this organism. The development of a vaccine against GAS has primarily targeted the abundant cell-surface protein called the M-protein. This review focuses on different M-protein-based-subunit vaccine approaches and the different delivery technologies used to administer these vaccine candidates in preclinical studies.

Pathogenesis of group A streptococcal infections

Group A streptococci are model extracellular gram-positive pathogens responsible for pharyngitis, impetigo, rheumatic fever, and acute glomerulonephritis. A resurgence of invasive streptococcal diseases and rheumatic fever has appeared in outbreaks over the past 10 years, with a predominant M1 serotype as well as others identified with the outbreaks. emm (M protein) gene sequencing has changed serotyping, and new virulence genes and new virulence regulatory networks have been defined. The emm gene superfamily has expanded to include antiphagocytic molecules and immunoglobulin-binding proteins with common structural features. At least nine superantigens have been characterized, all of which may contribute to toxic streptococcal syndrome. An emerging theme is the dichotomy between skin and throat strains in their epidemiology and genetic makeup. Eleven adhesins have been reported, and surface plasmin-binding proteins have been defined. The strong resistance of the group A streptococcus to phagocytosis is related to factor H and fibrinogen binding by M protein and to disarming complement component C5a by the C5a peptidase. Molecular mimicry appears to play a role in autoimmune mechanisms involved in rheumatic fever, while nephritis strain-associated proteins may lead to immune-mediated acute glomerulonephritis. Vaccine strategies have focused on recombinant M protein and C5a peptidase vaccines, and mucosal vaccine delivery systems are under investigation.

Is the pathogen of prion disease a microbial protein?

Though considerable circumstantial evidence suggests that the pathogen of prion disease is proteinaceous, it has not yet been conclusively identified. Epidemiological observations indicate that a microbial vector is responsible for the transmission of natural prion disease in sheep and goats and that the real causative agent may correspond to a structural protein of that microorganism. The microbial protein should resemble prion protein (PrP) and may replicate itself in the host by using mammalian DNA. A similar phenomenon was already described with a protein antigen of the ameba Naegleria gruberi. The various serotypes of the microbial protein may account for the existence of scrapie strains. It is proposed that many microbial proteins may be capable of replicating themselves in mammalian cells eliciting and sustaining thereby degenerative and/or autoimmune reactions subsequent to infections with microorganisms.

Serum and mucosal antibody isotype responses to M-like protein (SeM) of Streptococcus equi in convalescent and vaccinated horses

Equine strangles, caused by the clonal pathogen Streptococcus equi, is a source of serious economic loss despite the widespread use of commercial vaccines. The anti-phagocytic 58 kDa M-like protein (SeM) is an important protective antigen. The objective of this study was to define differences, if any, between SeM-specific convalescent serum and mucosal IgA and IgG subisotypes and those induced by vaccination with commercial strangles vaccine. SeM-specific opsonophagocytic IgGb was the predominant serum antibody in horses intramuscularly vaccinated or recently recovered from infection. Infection also induced high levels of specific opsonophagocytic serum IgGa during and shortly after S. equi infection whereas vaccination stimulated only low levels of serum IgGa. Specific serum IgGc and opsonophagocytic IgA were present at very low levels following infection or vaccination. A strong specific mucosal antibody response occurred during the acute and convalescent phases of infection whereas vaccinated horses made no mucosal response. Specific IgGb was generally predominant in nasopharyngeal washings during the acute phase but was replaced by specific IgA during convalescence. SeM-specific mucosal IgGa and IgG(T) but not IgGc were detected only during the acute and early convalescent phase. The results therefore indicate that vaccination, although inducing SeM-specific serum isotype responses qualitatively and quantitatively similar to those seen in convalescence, did not induce mucosal responses. This suggests that mucosal immunity may be important in acquired resistance to strangles.

Streptococcus pyogenes type M12 protein shows selective binding to some human immunoglobulin G3 myeloma proteins

Purified, recombinant M12 protein from Streptococcus pyogenes CS24 has recently been demonstrated to bind human immunoglobulin G3 (IgG3). The binding site for IgG has been localized to an internal peptide encoded by a PvuII fragment of the gene emm12. We have investigated the ability of an isolated recombinant M12 protein consisting of the peptide encoded by the PvuII fragment to bind various monoclonal human IgG3 myeloma proteins representing a number of both Caucasian and Oriental IgG3 Gm(allotypic) phenotypes. Of nine Caucasian IgG3 myeloma proteins, only two bound strongly to the recombinant M12 protein in enzyme-linked immunosorbent assays. The allotypic phenotypes of the reactive proteins were IgG3m(b+)(g-) and IgG3m(b-)(g+). No binding was seen for seven IgG3 myeloma proteins of Oriental origin with G3m(st+)(u-)(b+)(g-), G3m(st-)(u+)(b+)(g-), G3m(st-)(u+)(b-)(g+), and G3m(st-)(u-)(b-)(g+) phenotypes. The binding of human IgG3 to M12 protein seems to be related to features other than its Gm allotypic markers. Selective reactivity of IgG3 myeloma proteins with M12 protein may provide another way to subclassify human IgG3 molecules. The biological significance of the selective reactivity is not known.

A method for allelic replacement that uses the conjugative transposon Tn916: deletion of the emm6.1 allele in Streptococcus pyogenes JRS4

The emm6.1 allele of Streptococcus pyogenes JRS4 was deleted by using the conjugative transposon Tn916. The aphA-3 gene, conferring resistance to kanamycin, was cloned between the sequences flanking the structural gene for the type 6 M protein (emm6.1) and inserted into the BstXI site of Tn916 to generate the chimeric transposon Tn916-5K3. Because the BstXI site lies in a nonessential region of Tn916, the chimeric transposon could transfer by conjugation from Bacillus subtilis into JRS4. In some of the transconjugants, Tn916-5K3 replaced the emm6.1 locus of JRS4 by homologous recombination between the cloned emm6.1-flanking regions and the resident chromosome. One recombinant studied in detail, JRS75, was kanamycin resistant and tetracycline sensitive and lacked immunologically detectable M6 protein. Furthermore, by Southern blot analysis, the DNA region encompassing the emm6.1 structural gene was found to have been replaced by aphA-3.

Ultrastructural localization of the fibrinogen-binding domain of streptococcal M protein

Binding of fibrinogen to the M protein located on the surface fibrillae of group A streptococci impedes deposition of complement and thus contributes to the virulence of these organisms. We investigated this binding by electron microscopy using postembedding immunogold labeling. Both fibrinogen and its D fragment formed a distinct dense layer in the surface fibrillae, separated by 10 nm from the compact part of the cell wall. Labeling the sections with anti-fibrinogen or anti-fragment D showed that the fibrinogen-binding region lay within a 25-nm segment of the fibrillae beginning approximately 30 nm from the inner surface of the cell wall. The outer surface of the fibrinogen layer could be labeled with antibody to the amino-terminal half of type 24 M protein, indicating that the fibrillar tips remained exposed after fibrinogen binding. The degree of labeling with anti-fibrinogen, determined by gold particle counting, was the same whether the bacterial cells had been incubated with purified fibrinogen or whole plasma. These results indicate that the fibrinogen-binding region lies in the distal (amino-terminal) half of the M protein molecule but excludes the most distal portion, which is the site of epitopes that interact with opsonic anti-M antibody, and that plasma proteins other than fibrinogen, a number of which are known to bind to group A streptococci, do not interfere with fibrinogen binding.

Streptococcal M protein: molecular design and biological behavior

M protein is a major virulence determinant for the group A streptococcus by virtue of its ability to allow the organism to resist phagocytosis. Common in eucaryotes, the fibrillar coiled-coil design for the M molecule may prove to be a common motif for surface proteins in gram-positive organisms. This type of structure offers the organism several distinct advantages, ranging from antigenic variation to multiple functional domains. The close resemblance of this molecular design to that of certain mammalian proteins could help explain on a molecular level the formation of epitopes responsible for serological cross-reactions between microbial and mammalian proteins. Many of the approaches described in the elucidation of the M-protein structure may be applied for characterizing similar molecules in other microbial systems.

Cloning and expression of the streptococcal C5a peptidase gene in Escherichia coli: linkage to the type 12 M protein gene

A genomic library of Streptococcus pyogenes CS24 DNA was constructed by cloning streptococcal DNA partially digested with Sau3A into the lambda replacement vector EMBL3. The expression of streptococcal C5a peptidase (SCP) was analyzed by radioimmunoassay with hyperimmune rabbit serum. Two clones, lambda 4.1 and lambda 4.2, were found to express the desired antigen, and various DNA fragments from the hybrid bacteriophage lambda 4.1 were subcloned into the plasmid vector pUC9 in Escherichia coli. One of the recombinant plasmids, designated pTT1, contained a 5.8-kilobase (kb) streptococcal DNA insert. Analysis of total cellular protein from this E. coli clone by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western (immuno-) blotting identified a 140,000-Mr protein, similar in size to the native protein purified from S. pyogenes. Cloned SCP was functionally active, as shown by its ability to inhibit C5a-mediated chemotaxis. By deletion analysis with both restriction endonucleases and BAL 31 nuclease, the SCP gene was localized to a 4.3-kb segment of DNA. Southern hybridization experiments showed that the type 12 M protein-coding sequence is also present in the hybrid phage lambda 4.1, at approximately 2 kb upstream of the SCP structural gene. Western blot analysis indicated that the cloned streptococcal DNA in lambda 4.1 directed the expression of both SCP and M12 protein.

Cell surface proteins of a group A streptococcus type M4: the IgA receptor and a receptor related to M proteins are coded for by closely linked genes

Two genes coding for cell surface proteins were cloned from a group A streptococcus type M4: the gene for an IgA binding protein and the gene for a fibrinogen binding protein. Both proteins were purified and partially characterized after expression in Escherichia coli. There was no immunological cross-reaction between the two proteins. The IgA binding protein, called protein Arp4, is similar to an IgA receptor previously purified from another strain of group A streptococci, but the proteins are not identical. Characterization of many independent clones showed that the two proteins described here are coded for by closely linked genes. Bacterial mutants have been found which have simultaneously lost the ability to express both genes, and a simple method to isolate such mutants is described. The existence of these variants indicates that expression of the two cell surface proteins may be coordinately regulated. Binding of fibrinogen is a characteristic property of streptococcal M proteins, and the available evidence suggests that the fibrinogen binding protein is indeed an M protein.

Influence of intranasal immunization with synthetic peptides corresponding to conserved epitopes of M protein on mucosal colonization by group A streptococci

A major virulence factor of group A streptococci is M protein, a surface-exposed fibrillar molecule of which there exist more than 80 distinct serological types. Antigenic variability resides largely in the amino-terminal region of M protein, whereas the carboxy-terminal half of the molecule is highly conserved among different M serotypes. We sought to determine whether mucosal immunization with conserved epitopes of M protein influences the course of mucosal colonization by group A streptococci in a mouse model. Synthetic peptides corresponding to sequences in the conserved region of M protein were covalently linked to the mucosal adjuvant cholera toxin B subunit. Mice were immunized intranasally with the peptide-cholera toxin B subunit conjugate or with cholera toxin B subunit alone and then challenged intranasally with live streptococci. Pharyngeal colonization by streptococci was measured for up to 15 days postchallenge. Mice immunized with synthetic peptides showed a significant reduction in colonization compared with the control group. The data demonstrate that immunity evoked by conserved portions of M protein influences the outcome of group A streptococcal infection at the nasopharyngeal mucosa in a mouse model.

Conservation of protective and nonprotective epitopes in M proteins of group A streptococci

Carefully controlled hybridization experiments with probes from a cloned serotype 5 M protein (M5) gene (smp5) were performed with DNA isolated from heterologous M types of group A streptococci, and the homologies detected by hybridization were compared with the ability of anti-pepM5 serum to cross-opsonize heterologous M types. As previously reported (J.R. Scott, S.K. Hollingshead, and V.A. Fischetti, Infect. Immun. 52:609-612, 1986), extensive structural homologies exist among the 3' ends of heterologous M protein genes, but there appears to be an increase in sequence variation as one moves towards the 5' ends. However, a clear, predictive correlation between the hybridization patterns and cross-opsonization was not observed. Antibodies raised to a synthetic peptide corresponding to central, conserved sequences adjacent to the C-terminal sides of the pepsin cleavage sites in M5, serotype 6 M protein, and serotype 24 M protein cross-reacted with heterologous acid-extracted M antigens but were not protective and did not bind to intact streptococcal cells, indicating that these epitopes are inaccessible on the intact cell surface. Removal of the N-terminal half of M5, serotype 6 M protein, or serotype 24 M protein by pepsin exposed the conserved epitope on the cell surface. These results suggest that immunoaccessible protective epitopes are confined to the highly variable N-terminal halves of M proteins and that a single, broadly conserved protective M protein epitope does not exist.

Immunologic and genetic comparison of Streptococcus equi isolates from the United States and Europe

A series of isolates of Streptococcus equi from the United States and Europe were compared by the bactericidal test, immunoblotting, DNA restrictions, and Southern hybridization analysis. All isolates tested were sensitive to the same bactericidal serum. In addition, immunoblotting revealed no differences in M proteins prepared by acid or mutanolysin extraction. Immunoblotting of acid extracts of the isolates with mucosal nasopharyngeal mucus from a convalescent horse revealed the presence of the 41,000- and 46,000-Mr polypeptide fragments of the M protein of S. equi known to be important in stimulating mucosal nasopharyngeal immune responses. DNA restriction analysis of total cell DNA digests, as well as Southern hybridizations using an S. equi M protein gene probe, did not detect any differences among these isolates. Our results, therefore, confirm the antigenic homogeneity of the M proteins of S. equi isolates and suggest that variation in this antigen is not a reason for the failure of commercial vaccines in the field. Interestingly, the protoplast M proteins of all isolates showed remarkable size homogeneity, in contrast to the size variation reported in M proteins of group A streptococci.

Passive acquired mucosal immunity to group A streptococci by secretory immunoglobulin A

We present a model in which animals are passively immunized at a mucosal site, allowing one to evaluate immunological protection at the mucosal level only. Affinity-purified, anti-M protein sIgA administered intranasally protected mice against systemic infection after intranasal challenge with group A streptococci. In contrast, anti-M protein serum Ig administered intranasally was not protective at this site, although it neutralized the antiphagocytic property of M protein and promoted phagocytosis. Protection by sIgA occurred despite the lower immunoreactivity of sIgA to purified M protein compared with serum Ig. The data suggest that sIgA can protect at the mucosa and may preclude the need for opsonic IgG in preventing streptococcal infection.

Molecular evolution of streptococcal M protein: cloning and nucleotide sequence of the type 24 M protein gene and relation to other genes of Streptococcus pyogenes

The structural gene for the type 24 M protein of group A streptococci has been cloned and expressed in Escherichia coli. The complete nucleotide sequence of the gene and the 3' and 5' flanking regions was determined. The sequence includes an open reading frame of 1,617 base pairs encoding a pre-M24 protein of 539 amino acids and a predicted Mr of 58,738. The structural gene contains two distinct tandemly reiterated elements. The first repeated element consists of 5.3 units, and the second contains 2.7 units. Each element shows little variation of the basic 35-amino-acid unit. Comparison of the sequence of the M24 protein with the sequence of the M6 protein (S. K. Hollingshead, V. A. Fischetti, and J. R. Scott, J. Biol. Chem. 261:1677-1686, 1986) indicates that these molecules have are conserved except in the regions coding for the antigenic (type specific) determinant and they have three regions of homology within the structural genes: 38 of 42 amino acids within the amino terminal signal sequence, the second repeated element of the M24 protein is found in the M6 molecule at the same position in the protein, and the carboxy terminal 164 amino acids, including a membrane anchor sequence, are conserved in both proteins. In addition, the sequences flanking the two genes are strongly conserved.

Cloning and expression of the gene for an immunoglobulin G Fc receptor protein from a group A streptococcus

DNA containing the 5' end of the M-12 structural gene was used as a probe in colony hybridizations in an attempt to clone the M-76 gene from an M-type 76 group A streptococcal strain. A single positive colony was detected, and Southern hybridization analysis of plasmid DNA isolated from this colony indicated that the insert DNA had homology to the 5' end of the M-12 structural gene. Subclones were constructed to define the limits of the M-76 gene, and sonicates of these subclones were reacted with M-76-specific antiserum in immunodiffusion. A sonicate of one subclone, JM83(pDH56), reacted strongly with the M-76-specific antiserum but also reacted with preimmune rabbit serum. Protein expressed from this subclone bound immunoglobulin from horse and pig, as well as human myeloma immunoglobulin G (IgG) representing all four subclasses and purified human IgG Fc fragments. This indicated that JM83(pDH56) expressed a protein with characteristics previously attributed to the IgG Fc receptor protein from group A streptococci. Western blot analysis indicated that the cloned IgG Fc receptor protein had a molecular weight of approximately 29,000. Binding studies showed that the Fc receptor gene is expressed by the M-type 76 strain from which it was cloned and by an M- variant.

Serum bactericidal responses to Streptococcus equi of horses following infection or vaccination

An indirect test based on horse blood was used to study bactericidal responses of the horse to Streptococcus equi following infection or vaccination. Bactericidal antibody appeared in convalescent sera between two and four weeks and high titres were usually attained by eight weeks. Infection without clinical evidence of abscessation was also effective in eliciting strong bactericidal responses. Serum bactericidal activity of horses either recovered from strangles or immunised with commercial bacterin had declined eight months after vaccination. However, horses that developed strangles eight to 10 months after vaccination exhibited rapid and substantial increases in serum bactericidal activity. Groups of yearlings immunised with commercial S equi vaccines consisting either of M protein or bacterin developed clinical strangles within six months of vaccination although the majority of the animals had exhibited strong serum bactericidal activity a few weeks before occurrence of the disease. Similarly, a group of seven yearling ponies hyperimmunised with experimental vaccine, rich in M protein, were found to be highly susceptible to an intranasal challenge of 5 X 10(8) colony forming units of S equi, although their sera exhibited strong bactericidal activity at the time of challenge. These observations suggest that the role of serum bactericidal antibody in protection of the horse against strangles has been overrated.

Cloning and genetic analysis of serotype 5 M protein determinant of group A streptococci: evidence for multiple copies of the M5 determinant in the Streptococcus pyogenes genome

A gene bank of group A Streptococcus strain Manfredo (M protein serotype 5) was constructed with a bacteriophage lambda vector-Escherichia coli K-12 host system and screened by immunoblotting hybrid phage plaques with antisera raised to purified pep M5 (serotype 5 M protein fragment released from the streptococcal cell surface by pepsin). Hybrid phage expressing M5 antigen (lambda M5) were detected in the gene bank at an unexpectedly high frequency. The cloned streptococcal DNA sequences from one lambda M5 phage were subcloned into an E. coli plasmid vector. The M5 gene (smp5) was mapped, and its transcriptional orientation was determined by isolating and characterizing deletion and transposon insertion mutants of the M5+ hybrid plasmid pMK207. This analysis indicated that the intact smp5 gene had been cloned. Anti-pep M5 sera reacted with five pMK207-encoded polypeptides having relative molecular sizes of 64,000, 56,000, 55,500, 52,500, and 50,000. All of these polypeptides were encoded by the same DNA sequences, and all reacted with antisera raised to a synthetic peptide corresponding to the amino-terminal end of pep M5, suggesting that proteolytic cleavage at the carboxy-terminal end of the smp5 gene product generates at least some of the lower relative molecular size forms. Southern blotting experiments with smp5 gene sequences as probes identified multiple copies of DNA sequences sharing homology with the smp5 gene in the type 5 group A streptococcal genome.

Expression of protective and cardiac tissue cross-reactive epitopes of type 5 streptococcal M protein in Escherichia coli

The immunochemical properties of type 5 M protein antigens that were expressed in Escherichia coli K-12 by recombinant lambda bacteriophages isolated from a gene bank of serotype 5 Streptococcus pyogenes have been analyzed in detail. M proteins from partially purified bacteriophage lysates displayed precipitin lines of identity with a purified peptic extract of type 5 M protein (pep M5) in immunodiffusion assays. Immunoblot analyses of the M protein-positive lysates demonstrated that the cloned M protein component resided in five polypeptides with relative molecular weights of 57,900 (57.9K), 55.4K, 52.9K, 40.0K, and 32.6K. The hybrid lambda phage (lambda M5)-produced M protein contained immunoprotective epitopes; lambda M5 protein inhibited opsonization of type 5 streptococci by pep M5 antibodies, and antiserum raised against lambda M5 lysates opsonized type 5 streptococci. Each of the five antigenic polypeptides of the recombinant phage M protein also shared epitopes with human heart tissue, as demonstrated by the reactivity of immunoblots of lambda M5 antigens separated on sodium dodecyl sulfate gels with anti-pep M5 antibodies absorbed to and eluted from human heart sarcolemmal membranes. Moreover, antiserum raised against the lambda M5 lysates reacted with sarcolemmal membrane proteins with relative molecular weights of 200K, 59K, 55K, 53K, and 27K as determined by immunoblot analyses. These results demonstrate that the structural gene coding for type 5 streptococcal M protein which was inserted into lambda DNA expresses immunoprotective epitopes, some of which are shared with human heart tissue.

Mucosal nasopharyngeal immune responses of horses to protein antigens of Streptococcus equi

Mucosal nasopharyngeal immunoglobulin A (IgA) and IgG responses to proteins of Streptococcus equi were studied in horses after the experimental production of strangles. S. equi-specific IgA and IgG titers in nasopharyngeal mucus were much higher in samples from animals 1 to 2 weeks after challenge than in samples from control animals. Although IgA was the major immunoglobulin in nasal mucus, there was more antibody activity associated with IgG as measured by radioimmunoassay. Great differences between the specificities of antibodies in nasal mucus and in serum were detected. IgA and IgG of mucus origin recognized only two major proteins with molecular weights of about 41,000 and 46,000 in acid extracts of S. equi and gave no detectable reaction with culture supernatant proteins. Only one protein of about 62,000 molecular weight was recognized in acid extracts of an equine strain of S. zooepidemicus. In contrast, immunoglobulins in serum recognized a great variety of proteins in culture supernatants and acid extracts of S. equi and S. zooepidemicus which did not include those proteins recognized by immunoglobulins in mucus. These findings provide good evidence for the independence of the local and systemic immune responses of the horse to S. equi. Horses rechallenged shortly after recovery from the first infection were resistant to challenge with an inoculum of S. equi 10 times greater than that to which they were originally susceptible. This resistance appeared to be independent of the levels of bactericidal antibody in serum. We therefore suggest that immunity to S. equi infection is mediated by locally produced nasopharyngeal antibodies.

Presence of two distinct regions in the coiled-coil structure of the streptococcal Pep M5 protein: relationship to mammalian coiled-coil proteins and implications to its biological properties

The complete amino acid sequence of Pep M5, a biologically active 197-residue fragment comprising nearly half of the group A streptococcal M5 protein, has structural features characteristic of an alpha-helical coiled-coil protein. Fourier analyses of the nonpolar residues show strong periodicities based on repeats of 7 residues (7/2 and 7/3). Except for the nonhelical NH2-terminal 12-residue segment, the 7-residue periodicity in the distribution of nonpolar residues extends through the remainder of the Pep M5 molecule, with some discontinuities and irregularities. The molecule contains two distinct regions that differ in the pattern of distribution of the nonpolar and charged residues. The 7-residue pattern "a, b, c, d, e, f, g" in region 13-121 is atypical in that position "a" is predominantly occupied by asparagine, rather than nonpolar residues. On the other hand, the periodicity in region 122-196 is more typical of that found in other coiled-coil proteins, such as the myosin rod region, keratin, desmin, and vimentin, rather than tropomyosin. Although the periodicity in nonpolar residues is not highly regular, the predominance of basic and acidic residues in the inner "e" and "g" positions, respectively, suggests that ionic interactions between chains may contribute significantly to the stability of the coiled-coil. The distribution of charged residues in the outer positions within the two regions of the molecule is also distinct. The NH2-terminal region carries a significantly higher net negative charge than the COOH-terminal region, suggesting that the former region may play an important role in some of the biological functions of the Pep M5 molecule.

Small DNA deletions creating avirulence in Streptococcus pyogenes

The M protein is the antigen on the surface of group A streptococci that allows these bacteria to resist phagocytosis. DNA encoding the M12 protein was cloned into Escherichia coli and used as an isotopically labeled hybridization probe to compare genomic DNA's isolated from M+ and M- isogenic cultures in an effort to elucidate the genetic basis of this variation. DNA's from two spontaneous, independent M- variants contained small (approximately 50 base pairs) deletions which were mapped to identical restriction fragments within or adjacent to the M protein coding sequence. Taken together with the pleiotropic nature of these deletions, this suggests that they define a regulatory switch.

Common protective antigens of group A streptococcal M proteins masked by fibrinogen

The influence of fibrinogen on the opsonization of Group A streptococci by type-specific and cross-reactive anti-M protein antisera was investigated. As previously reported for type 24 streptococci, fibrinogen inhibited the complement-mediated opsonization of types 5, 6, and 19 organisms. Rabbit antisera against large peptide fragments of purified homologous M proteins (pep M proteins) overcame the anti-opsonic effect of fibrinogen in a dose-dependent manner. In the presence of optimal amounts of antibody, bacterial uptake by PMN was equal in serum and plasma, and greater than could be obtained in serum in the absence of antibody. Polyclonal anti-pep M sera contained antibodies directed against fibrinogen-binding as well as fibrinogen-nonbinding sites or regions of the M protein molecule. Three cross-reactive anti-pep M sera included antibodies directed against fibrinogen binding sites or regions of the cross-reacting M proteins. In the two sera studied in detail, these antibodies accounted for a large part of the cross-reacting anti-M antibody present in the sera. We suggest that fibrinogen binding sites on different serotypes of M protein may be structurally and therefore antigenically similar. Conservation of fibrinogen binding sites on M proteins may be related to their protective anti-opsonic function.

Surface characteristics of group A streptococci with and without M-protein

Twenty M protein-positive and eight M protein-negative strains of group A streptococci were investigated with respect to surface hydrophobicity and amount of lipoteichoic acid (LTA). Surface hydrophobicity as determined in polymer two-phase systems varied substantially between individual strains and there was no correlation to the presence of antiphagocytic M protein. The amount of LTA on the surface of the bacteria varied with hydrophobic affinity of the cells. Strains with a high content of surface LTA were found among both M-positive and M-negative streptococci. Cellular and extracellular LTA was estimated on six strains by the ability of hot phenol extracts and culture fluids to sensitize erythrocytes and by rocket immunoelectrophoretic quantitation. Differences in content of surface LTA did not correlate to differences in the total amount of cellular LTA. Pepsin digestion of M-positive group A streptococci at suboptimal pH resulted in a loss of M antigen whereas surface LTA and the hydrophobic interaction liability was retained. The results indicate that the degree of surface hydrophobicity as measured by two-phase partitioning is not correlated to either the type-specific or the antiphagocytic moiety of M protein. The results support the correlation between surface LTA and surface hydrophobicity of group A streptococci.

Receptor in group C and G streptococci detects albumin structures present in mammalian species

The presence of albumin structures with the capacity to bind to a surface receptor in group C and G streptococci was studied in serum samples from 45 mammalian species representing 15 different orders, using an inhibition assay. The ability of animal sera to inhibit the uptake of radiolabeled human serum albumin by the streptococci indicated the presence of such albumin structures. Positive reactions were found in species of most orders tested, with Marsupialia as a notable exception. All Carnivora sera tested were strongly positive. In some orders such as Artiodactyla both positive and negative species were identified. Serum samples from 62 bird species representing 15 orders and from 5 fish species were also tested in the inhibition assay. None of these serum samples was capable of inhibiting the uptake of human serum albumin by streptococci. Some differences were also noted in the results obtained with group C and G streptococci from human and bovine sources, respectively, indicating the presence of two types of receptors. The present studies suggest a phylogenetic origin of albumin structures with affinity for the streptococcal receptor to a period after the divergence of Marsupialia from the other mammalian orders.

Formation of molecular complexes between a structurally defined M protein and acylated or deacylated lipoteichoic acid of Streptococcus pyogenes

The orientation of lipoteichoic acid (LTA) molecules on the surface of bacterial cells undoubtedly is determined by the ability of the LTA, during its transit through the cell wall, to bind via its polyglycerophosphate backbone or its glycolipid moieties to other constituents of the cytoplasmic membrane and the cell wall. We have investigated the possibility that LTA may become anchored to the cell surface by binding through its polyanionic backbone to positively charged regions of cell wall proteins. LTA was found to prevent the precipitation of partially purified HCl extracts of several strains of streptococci as well as a structurally defined streptococcal M protein molecule (pep M24) in 83% solutions of ethanol. The formation of complexes between LTA and M protein was demonstrated further by immunoelectrophoresis of pep M24 protein with increasing concentrations of radiolabeled LTA and by using antiserum against pep M24 to develop precipitin arcs. Pep M24 electrophoresed alone produced a single precipitin arc close to the origin. In contrast, when electrophoresed as a mixture with LTA or deacylated LTA, the M protein produced a second precipitin arc toward the anode coinciding with the area of migration of the radioactive LTA. Increasing concentrations of LTA or deacylated LTA shifted increasing amounts of the pep M24 antigen to the region of the second arc. Maleylation of M protein to block the positively charged free amino groups before mixing it with LTA prevented the formation of complexes. The complexes formed by the M protein with LTA, but not with deacylated LTA, showed the capacity to bind bovine serum albumin; LTA had been shown previously to bind to the fatty acid binding sites on bovine serum albumin. These results indicate that the LTA molecule is able to bind via its polyanionic backbone to positively charged residues of surface proteins of cells of S. pyogenes. The implications of such interaction as to the orientation of LTA molecules on the surface of cells of S. pyogenes are discussed.

M antigens of group A streptococci isolated by means of immunochromatography. Biochemical and serological properties

M proteins of Streptococcus pyogenes types 1 and 12 were purified by immunochromatography on immobilized type-specific opsonizing antibodies. The M proteins were characterized serologically and biochemically. They absorb after immobilization opsonizing antibodies and only precipitate with homologous antisera in immunodiffusion. In SDS PAGE they show one main band, corresponding to mol. weights of 5 X 104 (type 1) and 5.4 X 104 (type 12), accompanied by faint lines, which form with the main band a precipitation line of identity in SDS-crossed immunoelectrophoresis. Both M proteins aggregate blood platelets and clot fibrinogen.

Potentiation of opsonization and phagocytosis of Streptococcus pyogenes following growth in the presence of clindamycin

Streptococcus pyogenes, bearing M-protein on its surface, resists opsonization by normal human serum and subsequent phagocytosis by human polymorphonuclear leukocytes. Previous studies have shown that M-protein positive organisms are poorly opsonized by the alternate pathway of complement. In an attempt to define further the role of the surface components of S. pyogenes in this process, we examined the ability of clindamycin, an antibiotic that inhibits protein biosynthesis, to alter bacterial opsonization. An M-protein positive strain of S. pyogenes was grown in varying concentrations of clindamycin at levels lower than those which inhibited growth, i.e., at levels less than the minimal inhibitory concentration. These bacteria were incubated with purified human polymorphonuclear leukocytes and peripheral blood monocytes. Significant enhancement of bacterial opsonization, phagocytosis, and killing resulted. Measurement of complement consumption and binding of the third component of complement (C3) onto the bacterial surface demonstrated that organisms grown in the presence of clindamycin activated complement more readily and fixed more C3 on their surface. Electron microscopy revealed the probable basis for these findings. Streptococci exposed to clindamycin during growth were largely denuded of surface "fuzz," the hairlike structures bearing M-protein. We conclude that the incorporation of clindamycin at concentrations that fail to inhibit growth of S. pyogenes nevertheless causes significant changes in the capacity of these bacteria to resist opsonization by serum complement. These findings support the hypothesis that M-protein inhibits bacterial opsonization by interfering with effective complement activation on the bacterial surface.

beta 2-Microglobulin is bound to streptococcal M protein

The presence of receptors for three human proteins (fibrinogen, IgG, and beta 2-microglobulin (beta 2m)) was studied in group A streptococcal strains. M type 1, 12 and 14, and in M protein-negative variants of these strains. Fibrinogen binding was detected in all six strains. IgG did not bind to the two type-12 strains and uptake was low in both type-14 strains. The type-1, M protein-positive strain was negative in binding experiments with radiolabelled IgG, whereas the M protein-negative variant was strongly positive. Aggregated beta 2m showed a high degree of reactivity with the M protein-positive strains but not with the corresponding M protein-negative variants. The results indicate that the receptor for aggregated beta 2m is located on M protein in group A streptococci.

Hyaluronate capsule prevents attachment of group A streptococci to mouse peritoneal macrophages

The antiphagocytic properties of the streptococcal hyaluronic acid capsule were explored in a system in which binding of the organism to the phagocyte, but not ingestion, could occur. The capsule was found to be highly effective in preventing attachment of two strains of group A streptococci to mouse peritoneal macrophages. Variation in attachment with phase of growth in broth culture (low in early log phase, high in late-log phase and thereafter) could be accounted for by production and subsequent loss of capsule. Hyaluronidase treatment removed the capsule and increased adherence; treatment with proteolytic enzymes removed M protein and decreased resistance to phagocytosis in whole human blood but did not remove the capsule or increase adherence to the mouse peritoneal macrophages.

Interactions of human neutrophils with leukotoxic streptococci

Most strains of Streptococcus pyogenes contain a toxin which can kill neutrophils. Previous workers failed to show any correlation between leukotoxin content and virulence of animals or humans. We examined the in vitro interactions of a leukotoxic streptococcus and a nonleukotoxic variant with human neutrophils. At ratios of 200 streptococcal colony-forming units per neutrophil, the toxic strain killed 92.8 +/- 2.0% of neutrophils, and the nontoxic strain killed only 9.0 +/- 1.2%. Despite this, ingestion of the two strains was equal. Postphagocytic oxidative metabolism was equivalent with low numbers of either toxic or nontoxic streptococci but depressed with high numbers of leukotoxic streptococci. At 20 min, neutrophils were able to kill leukotoxic (99.6 +/- 0.3% killed) and nonleukotoxic streptococci (99.5 +/- 0.2% killed) equally efficiently (P = 0.42). Thus, leukotoxicity does not interfere with the ability of neutrophils to destroy streptococci. This may explain why leukotoxicity does not appear to be an important factor in streptococcal virulence.

Tropomyosin-like seven residue periodicity in three immunologically distinct streptococal M proteins and its implications for the antiphagocytic property of the molecule

Partial sequences of three immunologically distinct group A streptococcal M proteins (M5, M6, and M24) revealed significant homology with each other, certain amino acid residues being conserved within the three molecules. In addition, a common feature of the sequenced regions of these M proteins was their high alpha-helical potential and the presence of a repeating seven residue periodicity that is characteristic of the double helical coiled-coil molecule, tropomyosin. The existence of a tropomyosin-like seven residue periodicity strongly suggests that regions of these three M proteins may participate in intra- and/or intermolecular coiled-coil interactions. Because of the constraints imposed by such a repeating periodicity, certain conserved residues within the M proteins would occupy spatially equivalent positions in the tertiary structure of these molecules. This common characteristic could play an important role in the common antiphagocytic property of the immunologically diverse M molecules. In addition to similarities in the secondary structure of M proteins and tropomyosin, significant sequence homology has also been observed between certain regions of these molecules with up to 50% identical residues. As a result of the striking structural similarity with tropomyosin, M proteins may play a regulatory role in the contractile mechanisms involved in phagocytosis.

Mitogenic and antigenic properties of group A streptococcal M protein preparations

The separation of a mitogenic substance in M protein preparations of Streptococcus pyogenes, type 1 and type 12, is described. The isolation was achieved by gel chromatography on Biogel A 0.5 m, and by immunochromatography on immobilized type specific antibodies. In the delayed cutaneous hypersensitivity test the immunochromatography purified M 1 protein caused erythema but no unspecific mitogenicity could be found by lymphocyte transformation test. In neutralization experiments the mitogenic activity of M protein preparations was specifically inhibited by anti-erythrogenic toxin antisera.

Purification and immunobiological properties of R antigen and its relation to M protein of type 3 group A Streptococcus

R protein was extracted from type 3 group A streptococci with hot (95 degrees C) HCl and was purified by ammonium sulfate precipitation followed by molecular-sieve and ion exchange chromatography. Although the R3 antigen was present in a heterogeneous population of proteins ranging from 78,000 to 100,000 daltons in size, we were able to separate an R-rich fraction that contained minimal amounts of heterogeneous proteins as indicated by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The final yield of the purified R protein was approximately 15 mug (dry weight) per g (wet weight) of washed and sedimented streptococci. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated a molecular size of approximately 78,000 daltons. Amino acid analysis showed lysine, glutamic acid, alanine, and aspartic acid as the predominant amino acids. A detailed comparison of the purified R3 protein with type 3 M protein indicated a similarity in composition and order of frequency of amino acids. However, the R3 antigen was found to be distinctive from the M3 antigen in agar gel diffusion tests. In addition, R3 and M3 proteins behaved differently in opsonophagocytosis tests and opsonization inhibition tests. Thus, R3 and M3 proteins produced precipitin lines of nonidentity with an unabsorbed antiserum against whole type 3 streptococci: M3-specific antiserum, but not R3-specific antiserum, enhanced the phagocytosis of type 3 streptococci. Purified M3 but not R3 protein was capable of inhibiting the type-specific opsonization of type 3 streptococci. The physicochemical resemblance between M and R proteins in general suggests a common genetic origin. Perhaps R proteins are variant forms of M proteins from which the antiopsonic determinant has been deleted.

Amino acid sequence and physicochemical similarities between streptococcal M protein and mammalian tropomyosin

The amino-terminal sequences of two peptides of type 24 streptococcal M protein show similarities with that of rabbit skeletal muscle tropomyosin, having up to 40% identical residues and probabilities of occurring by chance as low as P less than 10(-5). In addition, a hexapeptide (Glu-Ala-Glu-Lys-Ala-Ala) that is found five times in the M24 protein was shown to be identical to a sequence in tropomyosin. Similarities are also seen in the amino acid compositions and physicochemical properties of the two proteins. The amino-terminal sequences of peptides from another bacterial surface protein, staphylococcal protein A, are highly correlated with segments of two other myofibrillar proteins, rabbit actin (P less than 10(-7)) and rabbit myosin A1 light chain (P less than 10(-6)). The data presented suggest that a close structural relationship exists between mammalian muscle proteins and the biologically active surface proteins of staphylococci and streptococci. In addition, the correlation between sequences in M protein and tropomyosin represents direct evidence of a structural similarity at a molecular level between a streptococcal protein and a mammalian muscle component and may therefore prove relevant to the pathogenicity of the streptococcus.

The occurrence of a protein in the extracellular products of streptococci isolated from patients with acute glomerulonephritis

The present report compares the extracellular proteins of streptococci by sodium dodecyl sulfate polyacrylamide electrophoresis. A marked variation in the streptococcal extracellualr proteins (SEP) of different strains was detected, even in strains of similar serotypes. It was possible, however, to identify a single protein band that occurred predominantly in the SEP of strains isolated from patients with acute poststreptococcal glomerulonephritis (APSGN). This protein was generally not produced by streptococci obtained from patients without this disease. It appears to be immunologically similar in the various serotypes of streptococci isolated from patients with APSGN and can be demonstrated by immunofluorescence techniques to be present in the glomeruli of these patients.

Extraction of streptococcal type 12 M protein by cyanogen bromide

Conditions for the release of streptococcal type 12 M protein from whole cells by cyanogen bromide are described; they demonstrated that methionine is not essential to the structural arrangements which account for some of its immunological and biological properties. The released M protein was separated from other proteins by column chromatography with hydroxylapatite. The type-specific molecules which reacted with precipitating antibodies were found only in the 0.3 M eluate, formed zones with mobilities less than 12% of that of the dye front on electrophoresis in the standard acrylamide disc gel system, formed at least four bands in sodium dodecyl sulfate-acrylamide disc gels with molecular weights ranging from 12,000 to 23,000, and stimulated the formation of opsonic antibodies in rabbits. Cyanogen bromide provides a highly specific method for the release of M proteins which should prove particularly useful in analyses of structural-functional relationships among different M proteins.