Identification of a divergent M protein gene and an M protein-related gene family in Streptococcus pyogenes serotype 49

Horizontal gene transfer in the evolution of group A streptococcal emm-like genes: gene mosaics and variation in Vir regulons

Most M type 5 group A streptococcal strains were found to contain a single emm-like gene between virR and scpA (the Vir regulon), but two distinct emm-like genes were identified in the Vir regulon of the M5 strain NCTC8193. The complete sequences of both of these genes were determined. One, called emm5.8193, was shown to be a minor variant of the previously described emm5 gene from strain Manfredo. The second, designated enn5.8193, expresses an IgG-binding protein when cloned in Escherichia coli. A comparison of enn5.8193 with emm-like gene sequences from other strains indicated that it has a mosaic structure, consisting of distinct segments originating from emm-like genes in different OF+ and OF- strains. These data provide the first clear evidence that the horizontal transfer of emm-like sequences between distinct strains contributes to the evolution of group A streptococcal emm-like genes and Vir regulons.

Expression of foreign proteins on gram-positive commensal bacteria for mucosal vaccine delivery

Non-pathogenic Gram-positive oral commensal bacteria expressing recombinant fusion proteins on their cell surface have been successfully used to raise both a mucosal and a systemic immune response to foreign antigens while colonizing the oropharynx. In this system, fusion-protein vaccines are delivered and anchored to the surface of a commensal, which occupies the mucosal niche invaded by a particular pathogen. Surface expression of these foreign proteins is achieved by exploiting the common mechanism employed by Gram-positive bacteria for translocating and anchoring proteins to the cell surface. The process offers a safe alternative to the use of engineered pathogens as live vaccine delivery vehicles.

Association of type II immunoglobulin G-binding protein expression and survival of group A streptococci in human blood

Expression of immunoglobulin G (IgG)-binding proteins on group A streptococcus strain 64 was monitored on bacteria subjected to sequential passage in human blood. After approximately 10 cycles through human blood, strain 64 demonstrated enhanced levels of IgG-binding protein, including the expression of a type IIa binding molecule with an M(r) of approximately 47,000 present only at very low levels on the parent isolate. Changes in the expression of IgG-binding proteins after passage in human blood were similar to those observed when the same organism was passaged sequentially intraperitoneally in mice. Strain 64, passaged in human blood 23 times, was found to be more virulent than the parent isolate when used to infect mice either intraperitoneally or in a skin air sac. These findings suggest that the expression of IgG-binding proteins may be a common response of group A organisms to pressures exerted by distinct host defense mechanisms.

Nucleotide substitutions and small-scale insertion produce size and antigenic variation in group A streptococcal M1 protein

The presence of M protein on the surface of group A streptococci (GAS) confers the ability of the cell to resist phagocytosis in the absence of type-specific antibodies. It undergoes antigenic variation with more than 80 different serotypes having been defined. We have sequenced the M protein gene (emm1.1) from strain CS190 and present evidence that individual nucleotide substitutions are responsible for sequence variation in the N-terminal non-repeat region of emm1.1 and these substitutions have altered antibody recognition of opsonic epitopes. The N-terminal non-repeat domains of two other closely related strains, 71-155 and 76-088, were found to have sequence identical to emm1.1 with the addition of a 21 bp insert. This study provides the first evidence that nucleotide substitutions and small insertions are responsible for size and antigenic variation in the N-terminal non-repeat domain of the M protein of GAS.

Structural heterogeneity of the emm gene cluster in group A streptococci

One or more distinct copies of emm genes lie within a gene cluster that is located downstream from a transcriptional regulatory gene (mry). Mry is a positive regulator for the genes in this cluster and for the downstream gene, scpA. The objective of this study is to examine the structure of this cluster and the distribution of specific alleles within the cluster among group A streptococcal isolates of 32 different serotypes. The peptidoglycan (PG)-spanning domain, which exists in four divergent forms, was used to identify specific alleles of the genes within the emm cluster. Gene content of the cluster was determined by Southern hybridization with allele-specific oligonucleotides. Five different chromosomal patterns for this cluster were observed. Sequence heterogeneity in the adjacent mry locus was demonstrated by the ability of some of the isolates to hybridize with a whole mry gene probe, but not with mry-based oligonucleotide probes. A PCR-based chromosomal mapping technique was used to examine further the gene order within the emm gene clusters. Structural heterogeneity of the emm gene cluster was found within class I isolates in this study, while class II isolates were relatively homogeneous at this chromosomal locus and distinct from class I.

Positive transcriptional control of mry regulates virulence in the group A streptococcus

Transcription of the antiphagocytic M protein in the group A streptococcus (Streptococcus pyogenes) is environmentally regulated in response to CO2 and requires Mry, a trans-acting positive regulatory protein. We have examined the role of Mry in environmental regulation by analysing the factors that regulate expression of the gene that encodes Mry (mry). By employing a strategy that utilizes integrational plasmids, it was found that expression of mry requires the participation of DNA sequences that extend 473 base pairs upstream of the Mry coding region. Transcription of mry, as analysed in S1 nuclease protection assays, is initiated from two separate promoters located within this extended regulatory region. Construction and analysis of transcriptional fusions between the mry promoters and a promoterless chloramphenicol acetyltransferase gene demonstrated that mry is autoregulated and environmentally regulated in response to the level of CO2. These data suggest a model for the regulation of virulence in S. pyogenes where positive transcriptional control of mry in response to environmental stimuli regulates the expression of the M protein.

Characterization of a conserved helper-T-cell epitope from group A Streptococcal M proteins

We have previously defined major histocompatibility complex (MHC) class II-restricted T-cell epitopes from the carboxy-terminal region of group A streptococcal type 5 M protein. In this report, T-cell responses to one of these epitopes have been characterized in detail. T-cell clones from recombinant M5-immunized mice and popliteal lymph node cells from peptide-immunized mice were used to show that sM5[300-319] is recognized in the context of I-A alleles of four of nine independent MHC class II haplotypes: I-Ad, I-Af, I-Ak, and I-As. This epitope was also recognized by both helper (Th2) and inflammatory (Th1) subsets of murine T cells. The I-Ad-restricted epitope recognized by BALB/c mice was mapped to the 12-amino-acid peptide sM5[308-319] and was shown to provide helper function for an immunoglobulin G anti-peptide antibody response in BALB/c mice. Anti-peptide antibody was shown to be specific for M5[304-315] but failed to recognize intact rM5, suggesting that the conformation of the epitope differed between peptide and protein. However, the results demonstrate that overlapping epitopes can be the focus for both immunoglobulin G antibodies and the T cells which augment their production. Comparison of the available sequences for M proteins indicated that the T-cell epitope within M5[300-319] was highly conserved between M types and hence may elicit helper function for protective antibody responses to a wide range of M types. T-cell epitopes from conserved regions of M proteins which are recognized in the context of multiple MHC haplotypes have potential for the design of multivalent streptococcal vaccines.

Three different types of organization of the vir regulon in group A streptococci

The DNA of group A streptococci (GAS) encodes several important virulence factors such as the antiphagocytic M protein, the Ig-Fc-binding M-related proteins (FcrA-like and EnnX-like) and the complement factor-inactivating C5a peptidase. The corresponding genes emm, fcrA, ennX, and scpA, respectively, were assumed to be located close together in the GAS genome. Additionally, emm and scpA have been found to be under the positive, coordinate control of the virR locus, which led to the designation "vir regulon" for the corresponding genomic segment. In order to map the vir regulons of many GAS serotypes and to analyse any correlation between the organization of vir regulons and circumscribed heterogeneities within the emm, virR, and scpA genes, an approach using several distinct sets of polymerase chain reaction (PCR) experiments was chosen. By examination of the genomic DNA of 42 GAS isolates from 36 different M serotypes three patterns of vir regulon topography were found. The first, designated "large vir regulon" (LVR), consists of virR--fcrA(-like)--emm--ennX(-like)--scpA. The second, designated "small vir regulon" (SVR), contains virR--emm--scpA, and the last, designated "unusual vir regulon" (UVR), resembles SVR but contains additional heterogeneous sequences between emm and scpA. The patterns correlate with heterogeneities at the 3' ends of the virR and scpA genes, with the M classification system and the occurrence of specific non-coding intervening sequences within the vir regulons. The potential impact of these patterns on models to account for generation of vir regulons is discussed.

Hyaluronate synthase: cloning and sequencing of the gene from Streptococcus sp

The complete nucleotide sequence of hyaluronate synthase from Streptococcus sp. and its flanking regions is presented. The gene locus was designated has. Southern-blotting results suggested that the gene was conserved in hyaluronate-producing streptococci. A putative translation-initiation codon was identified and the open reading frame consists of 1566 bp, specifying a protein of 56 kDa. Sequences resembling the promoter and ribosome-binding site of Gram-positive organisms are found upstream of the synthase. The predicted amino-acid sequence reveals the presence of a 35-residue signal peptide. The sequence has some similarity to bacterial peptide-binding proteins.

Identification of sequence types among the M-nontypeable group A streptococci

Streptococcal diseases, namely, acute glomerulonephritis and acute rheumatic fever, are common features in the aboriginal population of the Northern Territory of Australia. We examined the group A streptococcal M types identified during various surveys conducted since 1987. Streptococci were predominantly isolated from skin infections. A high proportion of the isolates could not be serotyped by conventional means and were designated M nontypeable (MNT). M-specific DNA sequences from the MNT isolates were examined, and sequence types were proposed for the classification of MNTs. This allowed a more precise estimate of the M types present in a population study.

Functional and serological analysis of type II immunoglobulin G-binding proteins expressed by pathogenic group A streptococci

Bacterial immunoglobulin-binding proteins expressed on the surface of group A streptococci represent a heterogeneous family of functionally related proteins. In this report, we describe efficient methods for extracting immunoglobulin-binding proteins and classifying them functionally and antigenically. A common characteristic of immunoglobulin-binding proteins expressed by group A streptococci appears to be the absence of internal methionine residues in the binding protein. This has enabled development of a rapid, efficient, cyanogen bromide-based extraction procedure for solubilizing these molecules from intact bacteria. Studies carried out with a series of monospecific polyclonal antibodies prepared in chickens have identified two major antigenic classes of immunoglobulin-binding proteins. The methods described in this report facilitate a rapid functional and serological screening of immunoglobulin-binding proteins that should now enable detailed epidemiological studies of the importance of these molecules in group A streptococcal infections and their relationship to other surface proteins, in particular, the antiphagocytic M protein.

Large, identical, tandem repeating units in the C protein alpha antigen gene, bca, of group B streptococci

Group B Streptococcus (GBS) is the leading cause of neonatal sepsis and meningitis in the United States. The surface-associated C protein alpha antigen of GBS is thought to have a role in both virulence and immunity. We previously cloned the C protein alpha antigen structural gene (named bca for group B, C protein, alpha) into Escherichia coli. Western blots of both the native alpha antigen and the cloned gene product demonstrate a regularly laddered pattern of heterogeneous polypeptides. The nucleotide sequence of the bca locus reveals an open reading frame of 3060 nucleotides encoding a precursor protein of 108,705 Da. Cleavage of a putative signal sequence of 41 amino acids yields a mature protein of 104,106 Da. The 20,417-Da N-terminal region of the alpha antigen shows no homology to previously described protein sequences and is followed by a series of nine tandem repeating units that make up 74% of the mature protein. Each repeating unit is identical and consists of 82 amino acids with a molecular mass of 8665 Da, which is encoded by 246 nucleotides. The size of the repeating units corresponds to the observed size differences in the heterogeneous ladder of alpha C proteins expressed by GBS. The C-terminal region of the alpha antigen contains a membrane anchor domain motif that is shared by a number of Gram-positive surface proteins. The large region of identical repeating units in bca defines protective epitopes and may play a role in generating phenotypic and genotypic diversity of the alpha antigen.

Two major classes in the M protein family in group A streptococci

The M protein family of molecules in the group A streptococcus comprises a number of cell surface proteins that interact with the immune system of the host. One of the proteins in this family is the IgA receptor Arp4, which has C repeats similar to those that characterize the known M proteins. The streptococcal strain expressing Arp4 also expresses a second immunoglobulin-binding protein, Mrp4, which is shown here to be encoded by a gene located immediately upstream of the gene for Arp4. In addition to binding IgG, Mrp4 also binds fibrinogen, a property ascribed to M proteins. DNA sequence analysis demonstrated that the Mrp4 protein indeed is a member of the M protein family, but it was unexpectedly found to have a type of repeat that is identical to the A repeat described for FcRA76, a partially sequenced streptococcal Fc receptor. Purified FcRA76 was shown to bind fibrinogen and IgG, like Mrp4. These data show that the known molecules in the M protein family can be divided into two classes, A and C, according to the type of repeat region found. Hybridization studies with a panel of clinical isolates indicate that many streptococcal strains express class A and class C proteins, whereas some strains express only class C proteins. Class A molecules show amino-terminal sequence variation, like class C molecules, which suggests that proteins of both classes are targets for the immune response.

M protein gene typing of Streptococcus pyogenes by nonradioactively labeled oligonucleotide probes

A new approach for the typing of Streptococcus pyogenes is described. Oligonucleotide probes of 30 nucleotides in length were derived from currently known sequences of the N-terminal regions of M protein genes (emm genes). The oligonucleotides were labeled with digoxigenin-dUTP and hybridized to dot-blotted genomic DNA from 116 group A streptococcal strains of serotypes M-1, M-2, M-3, M-5, M-6, M-12, M-18, M-19, M-24, and M-49. Hybridization reactions were visualized with a chemiluminescent substrate. In comparison with conventional serological typing of expressed M proteins, the binding of the probes to the corresponding emm genes exhibited 100% sensitivity and specificity. The results emphasize the high degree of type-specific conservation of the N-terminal regions of emm genes from reference strains and epidemiologically unrelated U.S. and European clinical isolates. The existence of two distinct genetic subgroups among eight investigated M-49 strains was unequivocally shown by hybridization assays and further confirmed by nucleotide sequence data obtained from four selected M-49 strains. Because oligonucleotide probes are relatively easy to prepare, easy to handle, and known to give consistent interlaboratory results, the "oligotyping" technique appears to offer potential advantages over conventional serological typing methods.

The group A streptococcal M-type 3 protein gene exhibits a C terminus typical for class I M proteins

The M protein gene (emm gene) from a reference group A streptococcal strain of serotype M3 was amplified by the polymerase chain reaction and partially sequenced. Hybridization assays using an oligonucleotide probe derived from the N-terminal sequence revealed that this gene segment is highly homologous among M-type 3 isolates. Of note, analysis of the nucleotide sequence data from the C terminus of the gene confirmed that the emm 3 gene exhibited all the features characteristic for group A streptococcal M-class I molecules. Recently published sequence data that were assigned to emm 3 resulted from a strain confusion and were shown to be the first one derived from an emm gene of an M-untypable isolate.

Fibronectin-binding protein of Streptococcus pyogenes: sequence of the binding domain involved in adherence of streptococci to epithelial cells

The sequence of the fibronectin-binding domain of the fibronectin-binding protein of Streptococcus pyogenes (Sfb protein) was determined, and its role in streptococcal adherence was investigated by use of an Sfb fusion protein in adherence studies. A 1-kb DNA fragment coding for the binding domain of Sfb protein was cloned into the expression vector pEX31 to produce an Sfb fusion protein consisting of the N-terminal part of MS2 polymerase and a C-terminal fragment of the streptococcal protein. Induction of the vector promoter resulted in hyperexpression of fibronectin-binding fusion protein in the cytoplasm of the recombinant Escherichia coli cells. Sequence determination of the cloned 1-kb fragment revealed an in-frame reading frame for a 268-amino-acid peptide composed of a 37-amino-acid sequence which is completely repeated three times and incompletely repeated a fourth time. Cloning of one repeat into pEX31 resulted in expression of small fusion peptides that show fibronectin-binding activity, indicating that one repeat contains at least one binding domain. Each repeat exhibits two charged domains and shows high homology with the 38-amino-acid D3 repeat of the fibronectin-binding protein of Staphylococcus aureus. Sequence comparison with other streptococcal ligand-binding surface proteins, including M protein, failed to reveal significant homology, which suggests that Sfb protein represents a novel type of functional protein in S. pyogenes. The Sfb fusion protein isolated from the cytoplasm of recombinant cells was purified by fast protein liquid chromatography. It showed a strong competitive inhibition of fibronectin binding to S. pyogenes and of the adherence of bacteria to cultured epithelial cells. In contrast, purified streptococcal lipoteichoic acid showed only a weak inhibition of fibronectin binding and streptococcal adherence. These results demonstrate that Sfb protein is directly involved in the fibronectin-mediated adherence of S. pyogenes to epithelial cells.

Surface protein-CAT reporter fusions demonstrate differential gene expression in the vir regulon of Streptococcus pyogenes

Streptococcus pyogenes expresses at least two virulence factors, the anti-phagocytic M protein and an inhibitor of chemotaxis, the C5a peptidase (ScpA), under control of the virR locus. To facilitate studies of this regulatory unit, we constructed a new shuttle vector with a staphylococcal chloramphenicol acetyl transferase (CAT) reporter box which replicates in S. pyogenes. We cloned polymerase chain reaction (PCR)-derived potential promoter regions of the virR, M protein (emm12), and ScpA (scpA) genes from an M type 12 S. pyogenes, strain CS24. Promoter activity was assessed by measurements of specific mRNAs, transacetylase activity, and minimum inhibitory concentrations (MICs) for chloramphenicol resistance. We demonstrated that VirR is a necessary but not always sufficient positive trans-acting regulator of emm12 and scpA expression; however, virR is not autoregulated. A potential virR-binding consensus sequence is postulated for emm12, scpA and other M-like protein genes. Promoter activity of the structural genes was found to be dramatically influenced by growth conditions such as anaerobiosis. Levels of control, over and above the requirement for virR, are realized. The virR and scpA promoters were mapped for the first time using primer extension analysis. The observed mRNA start sites did not completely agree within the sequence predicted start sites. Data suggest that scpA could be subject to transcription attenuation.

Architecture of the vir regulons of group A streptococci parallels opacity factor phenotype and M protein class

Group A streptococci have traditionally been categorized into two broad groups based on the presence or absence of serum opacity factor (OF). Recent studies show that these two groups vary in a number of properties in addition to the OF phenotype, including sequence variations in the constant region of the antiphagocytic M protein genes, the presence or absence of immunoglobulin G Fc receptor proteins, and the presence or absence of multiple M protein-like genes situated in a tandem array. The M protein genes (emm) in OF- streptococcal strains are known to be part of a regulon of virulence-related genes controlled by the trans-acting positive regulatory gene, virR, situated just upstream of emm. In OF+ strains, however, the region adjacent to virR is occupied by an M protein-related, type IIa immunoglobulin G Fc receptor gene (fcrA), and the relative position of emm has not been determined. To further define the vir regulon in OF+ streptococci, we used the polymerase chain reaction to show that fcrA49 is situated immediately upstream of emm49 in the OF+ type 49 strain CS101. This result shows for the first time the separate identity and genetic linkage of these two genes in the vir regulon of an OF+ group A streptococcal strain and confirms our previous hypothesis that emm49 exists as the central gene in a trio of emm-like genes. Additionally, using DNA hybridizations, we found considerable sequence divergence between OF- and OF+ group A streptococci in virR and in the noncoding sequences between virR and the emm or fcrA expression site. We found, however, a high degree of sequence conservation in this region within each of the two groups of strains.

Expression of M6 protein gene of Streptococcus pyogenes in Streptococcus gordonii after chromosomal integration and transcriptional fusion

The M6 protein of Streptococcus pyogenes was expressed on the cell surface and secreted in Streptococcus gordonii Challis (formerly Streptococcus sanguis) after chromosomal integration of a promoterless M6 protein gene (emm-6.1). The ermC gene, conferring resistance to erythromycin, was cloned downstream of emm-6.1, within the same ClaI fragment. The initiation codon of emm-6.1 was 19 bp downstream of a ClaI site, so that ClaI cleavage would leave the gene promoterless. The ClaI fragment containing the promoterless emm-6.1 and ermC was ligated in vitro with a ClaI digest of S. gordonii chromosomal DNA. Random chromosomal integration of the heterologous DNA was obtained by using the ligation mixture to transform the naturally competent S. gordonii Challis. Twenty-eight percent of transformants selected for erythromycin resistance also expressed M6. Among the best M6 producers, 10 clones were selected for the stability of their phenotype. Nine of the 10 clones were shown to harbour one intact copy of the emm-6.1/ermC ClaI fragment integrated into the chromosome. These strains both expressed M6 protein on the surface and secreted different amounts of the molecule, since in each case the protein was produced after a transcriptional fusion of emm-6.1 with a different chromosomal promoter. A S. gordonii strain expressing large amounts of surface M6 protein, as judged by immunofluorescence and Western blot, was compared to the M- parental strain in a standard opsonophagocytosis assay. Of the isogenic pair, M6+ S. gordonii survived better in human blood and was phagocytosed at a slower rate.

Structural properties and evolutionary relationships of PspA, a surface protein of Streptococcus pneumoniae, as revealed by sequence analysis

Analysis of the sequence for the gene encoding PspA (pneumococcal surface protein A) of Streptococcus pneumoniae revealed the presence of four distinct domains in the mature protein. The structure of the N-terminal half of PspA was highly consistent with that of an alpha-helical coiled-coil protein. The alpha-helical domain was followed by a proline-rich domain (with two regions in which 18 of 43 and 5 of 11 of the residues are prolines) and a repeat domain consisting of 10 highly conserved 20-amino-acid repeats. A fourth domain consisting of a hydrophobic region too short to serve as a membrane anchor and a poorly charged region followed the repeats and preceded the translation stop codon. The C-terminal region of PspA did not possess features conserved among numerous other surface proteins, suggesting that PspA is attached to the cell by a mechanism unique among known surface proteins of gram-positive bacteria. The repeat domain of PspA was found to have significant homology with C-terminal repeat regions of proteins from Streptococcus mutans, Streptococcus downei, Clostridium difficile, and S. pneumoniae. Comparisons of these regions with respect to functions and homologies suggested that, through evolution, the repeat regions may have lost or gained a mechanism for attachment to the bacterial cell.

Nucleotide sequences of two adjacent M or M-like protein genes of group A streptococci: different RNA transcript levels and identification of a unique immunoglobulin A-binding protein

M protein is a key virulence factor present on the surface of group A streptococci. M protein is defined by its antiphagocytic function, whereas M-like proteins, while structurally related to M proteins, lack an established antiphagocytic function. Group A streptococci can be divided into two main groups (class I and II) on the basis of the presence or absence of certain antigenic epitopes within the M and M-like molecules, and importantly, the two classes correlate with the disease-causing potential of group A streptococci. In an effort to better understand this family of molecules, a 2.8-kb region containing the two M protein-like genes from a class II isolate (serotype 2) was cloned and sequenced. The two genes lie adjacent to one another on the chromosome, separated by 211 bp, and have many structural features in common. The emmL2.1-derived product (ML2.1 protein) is immunoreactive with type-specific antiserum, a property associated with M proteins. The cloned product of the downstream gene, emmL2.2 (ML2.2 protein), is an immunoglobulin A (IgA)-binding protein, binding human myeloma IgA. Interestingly, the RNA transcript levels of emmL2.1 exceed that of emmL2.2 by at least 32-fold. Northern (RNA) hybridization and primer extension studies suggest that the RNA transcripts of emmL2.1 and emmL2.2 are monocistronic. The ML2.1 and ML2.2 proteins exhibit 53% amino acid sequence identity and differ primarily in their amino termini and peptidoglycan-spanning domains and in a Glu-Gln-rich region present only in the ML2.1 protein. However, the previously described M-like, IgA-binding protein from a serotype 4 isolate (Arp4) displays a higher level of amino acid sequence homology with the ML2.1 molecule than with the IgA-binding ML2.2 protein. Amino acid sequence alignments between all M and M-like proteins characterized to date suggest the existence of two fundamental M or M-like gene subclasses within class II organisms, represented by emmL2.1 and emmL2.2. In addition, IgA-binding activity can be found within both types of molecules.

Application of the polymerase chain reaction to study the M protein(-like) gene family in beta-hemolytic streptococci

Evaluation of homologous regions of published M protein (emm) gene sequences from group A streptococci (GAS; Streptococcus pyogenes) was used to design three primer pairs for polymerase chain reaction (PCR) and three oligonucleotide probe sequences internal to the amplified products. One set of primers and corresponding probe should detect and lead to amplification of emm(-like) genes of virtually every type ("all M"), another ("SOR-M") should only amplify emm(-like) genes from GAS negative for serum opacity reaction (SOR) and the third ("SOR+ M") should expand only emm(-like) genes from SOR+ GAS. Using the "allM" primer pair for PCR on the genomic DNA from GAS of 29 different M types as well as from a group C and a group G streptococcal isolate, DNA fragments within the expected size range were amplified in every assay. All PCR products reacted with the "allM" probe. Related sequences were not detected in genomic DNA of an S. agalactiae and an Enterococcus faecalis isolate. Applying the "SOR-M" and "SOR+M" primers to identical assays led to mutually exclusive amplification products. The "SOR-M" and "SOR+M" probes hybridized only to their corresponding products. Exceptions to this exclusivity were the SOR- GAS of M types 3, 8, 27, 34, 42, 67, and 69, which consistently reacted only with the "SOR+M" primer/probe set. Analysis of sequence data from the amplified emm(-like) 2, 3, 18, and 19 genes revealed interesting specific features such as conserved gaps in the C-terminal sequence regions from SOR+ and the exceptional SOR- GAS strains. These data indicate the existence of a subgroup of strains among SOR- GAS and may advance our understanding of phylogenetic relationship between different serotypes of GAS.

Heptad motifs within the distal subdomain of the coiled-coil rod region of M protein from rheumatic fever and nephritis associated serotypes of group A streptococci are distinct from each other: nucleotide sequence of the M57 gene and relation of the deduced amino acid sequence to other M proteins

Streptococcal M protein, a dimeric alpha helical coiled-coil molecule, is an antigenically variable virulence factor on the surface of the bacteria. Our recent conformational analysis of the complete sequence of the M6 protein led us to propose a basic model for the M protein consisting of an extended central coiled-coil rod domain flanked by a variable N-terminal and a conserved C-terminal end domains. The central coiled-coil rod domain of M protein, which constitutes the major part of the M molecule, is made up of repeating heptads of the generalized sequence a-b-c-d-e-f-g, wherein "a" and "d" are predominantly apolar residues. Based on the differences in the heptad pattern of apolar residues and internal sequence homology, the central coiled-coil rod domain of M protein could be further divided into three subdomains I, II, and III. The streptococcal sequelae rheumatic fever (RF) and acute glomerulonephritis (AGN) have been known to be associated with distinct serotypes. Consistent with this, we observed that the AGN associated M49 protein exhibits a heptad motif that is distinct from the RF associated M5 and M6 proteins. Asn and Leu predominated in the "a" and "d" positions, respectively, in subdomain I of the M5 and M6 proteins, whereas apolar residues predominated in both these positions in the M49 protein. To establish whether the heptad motif of M49 is unique to this protein, or is a general characteristic of nephritis-associated serotypes, the amino acid sequence of M57, another nephritis-associated serotype, has now been examined. The gene encoding M57 was amplified by PCR, cloned into pUC19 vector, and sequenced. The C-terminal half of M57 is highly homologous to other M proteins (conserved region). In contrast, its N-terminal half (variable region) revealed no significant homology with any of the M proteins. Heptad periodicity analysis of the M57 sequence revealed that the basic design principles, consisting of distinct domains observed in the M6 protein, are also conserved in the M57 molecule. However, the heptad motif within the coiled-coil subdomain I of M57 was distinct from M5 and M6 but similar to M49. Similar analyses of the heptad characteristics within the reported sequences of M1, M12, and M24 proteins further confirmed the conservation of the overall architectural design of sequentially distinct M proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Virulent human strains of group G streptococci express a C5a peptidase enzyme similar to that produced by group A streptococci

Specific proteolytic destruction of the human chemotaxin, C5a, is a property of group A and B streptococcal pathogens. Here we show that virulent group G streptococci from human sources also express C5a peptidase activity. The enzyme responsible for this activity is approximately the same size as and is antigenically similar to that produced by group A streptococci. On the basis of Southern hybridization analysis with an internal fragment of the group A C5a peptidase gene (scpA) as a probe, a copy of this gene was found in the genome of all group G human isolates tested. Comparison of partial restriction maps of scpA and scpG revealed significant similarity between the two genes. Group G strains isolated from dogs and cows were found to lack C5a peptidase activity and did not hybridize to the scpA-specific probe. The association of this activity with three streptococcal species suggests that elimination of phagocyte chemotactic attractants is a more universal virulence mechanism than originally anticipated.

Entry of L. monocytogenes into cells is mediated by internalin, a repeat protein reminiscent of surface antigens from gram-positive cocci

We report the identification of a previously unknown gene, inlA, which is necessary for the gram-positive intracellular pathogen Listeria monocytogenes to invade cultured epithelial cells. The inlA region was localized by transposon mutagenesis, cloned, and sequenced. inlA was introduced into Listeria innocua and shown to confer on this normally noninvasive species the ability to enter cells. Sequencing of inlA predicts an 80 kd protein, internalin. Two-thirds of internalin is made up of two regions of repeats, region A and region B, and the C-terminus of the molecule is similar to that of surface proteins from gram-positive cocci. Internalin has a high content of threonine and serine residues, and the repeat motif of region A has regularly spaced leucine residues. As evidenced by Southern blot analysis, inlA is part of a gene family. One of them is the gene situated directly downstream of inlA, called inlB, which also encodes a leucine-rich repeat protein.

The amino-terminal region of group A streptococcal M protein determines its molecular state of assembly and function

Group A streptococcal M protein, a major virulence factor, is an alpha-helical coiled-coil dimer on the surface of the bacteria. Limited proteolysis of type 57 streptococcus with pepsin released two fragments of the M57 molecule, with apparent molecular weights of 32,000 and 27,000 on SDS-PAGE. However, on gel filtration under nondenaturing conditions, each of these proteins eluted as two distinct molecular forms. The two forms corresponded to their dimeric and monomeric state as compared to the gel filtration characteristics of known dimeric coiled-coil proteins. The results of sedimentation equilibrium measurements were consistent with this, but further indicated that the "dimeric form" consisted of a dimer in rapid equilibrium with its monomer, whereas the "monomeric form" does not dimerize. The monomeric form was the predominant species for the 27 kD species, whereas the dimeric form predominated for the 32 kD species. Sequence analysis revealed the 27 kD species to be a truncated derivative of the 32 kD PepM57 species, lacking the N-terminal nonheptad region of the M57 molecule. These data strongly suggested that the N-terminal nonheptad region of PepM57 is important in determining the molecular state of the molecule. Consistent with this, PepM49, another nephritis-associated serotype, which lacks the nonheptad N-terminal region, also eluted as a monomer on gel filtration under nondenaturing conditions. Furthermore, removal of the N-terminal nonheptad segment of the dimeric PepM6 protein converted it into a monomeric form. The dimeric molecular form of both the 32 kD PepM57 and the 27 kD PepM57 did not represent a stable state of assembly, and were susceptible to conversion to the corresponding monomeric molecular forms by simple treatments, such as lyophilization. The 27 kD PepM57 exhibited a greater propensity than the 32 kD species to exist in the monomeric form. The 32 kD species contained the opsonic epitope of the M57 molecule, whereas the 27 kD species lacked the same. This is consistent with the previous reports on the importance of the N-terminal region of M protein for its opsonic activity. Together, these results strongly suggest that, in addition to its importance for the biological function, the N-terminal region of the M protein plays a dominant role in determining the molecular state of the M molecule, as well as its stability.

Differentiation between two biologically distinct classes of group A streptococci by limited substitutions of amino acids within the shared region of M protein-like molecules

Group A streptococci can be categorized into two classes (I and II) based on immunodeterminants contained within a surface-exposed, conserved region (C repeat domain) of the major virulence factor, M protein. Previous studies have shown that several biological properties correlate strongly with streptococcal class, and thus, there is a strong impetus to precisely define the antigenic epitopes unique to class I and II M proteins. Using synthetic peptides, the binding sites of two class I-specific mAbs were mapped to distinct epitopes within the C repeat region of type 6 M protein (class I). A class II M protein-like gene (type 2) was cloned and sequenced, and the predicted amino acid sequence was compared for homology to class I and II molecules, whose sequences were previously reported. For a given C repeat block 35 amino acid residues in length, 20 residue positions were conserved among all sequences analyzed. Of the 15 variable amino acid positions, only four were class specific, and three of the four positions were localized in the area to which the class I-specific mAbs bound. The predicted secondary structures of class I and II C repeat blocks reveals that they are alpha-helical, except for a single area of disruption. In the class I molecules, the area of disruption corresponds to the class I-specific mAb binding sites. Importantly, the predicted conformational characteristics of this disruption differs for class I and II molecules. The data suggest that only limited changes in amino acid residues differentiate between class I and II molecules in the C repeat region. Therefore, selective (biological) pressures may have contributed to the evolution of these two classes of molecules.

Identification of group A type 1 streptococcal M protein gene by a non-radioactive oligonucleotide detection method

An oligonucleotide probe of 30 nucleotides length has been constructed, spanning the codons of amino acids 2 to 11 of the mature M1 protein of group A streptococci (Streptococcus pyogenes). It was labeled with digoxigenin-dUTP and visualized after hybridization with an anti-digoxigenin-antibody/alkaline phosphatase conjugate. It definitely detected the emm1 gene in dot-blotted 20-micrograms amounts of total nucleoid acid extracts. When tested with 27 type M1 group A streptococci of several epidemiologically unrelated outbreaks and 24 non-M1 strains, its sensitivity and specificity of detection reached 100% even at a hybridization temperature 35 degrees C below the calculated Tm. A detailed protocol for the construction and use of this oligonucleotide probe is given.

Domain structure and molecular flexibility of streptococcal M protein in situ probed by limited proteolysis

Serologically distinct group A streptococcal M proteins, the antiphagocytic determinants of the bacteria, have a highly repetitive sequence and exhibit a heptad periodicity characteristic of alpha-helical coiled-coil proteins. Based on the differences in the pattern of hepatad periodicity, the coiled-coil region of the complete M molecule has been divided into three distinct domains: I, II, and III. Domains I and II together constitute the variable part of M protein, whereas domain III is conserved among serotypes. Pepsin treatment of the M5, M6, and M24 streptococci results in a preferential cleavage of their M molecules between the predicted domains II and III, releasing biologically active fragments of the respective M proteins. Thus, a pepsin cleavage site at the junction of their variable and conserved regions is conserved in the M5, M6, and M24 proteins. In contrast, in the case of the M49 streptococci, the primary site of pepsin cleavage was observed to be within the conserved region of the M49 molecule, rather than at the junction of its variable and conserved regions. Despite containing part of the conserved region, the PepM49 protein is significantly smaller than the pepsin fragments of the M5, M6, and M24 proteins, which contain only the variable regions. However, in addition to the major PepM49 species, the pepsin digest of the type-49 streptococci also contained a smaller fragment, PepM49/a, as a minor component. Its formation was extremely sensitive to the pH of pepsin digestion. PepM49/a, which retains both the propensity to attain an alpha-helical conformation and the opsonic antibody epitope of the M49 molecule, contains only domains I and II like the other PepM proteins. Thus, as in the M5, M6, and M24 proteins, a pepsin cleavage site at the junction of the variable and conserved regions is indeed present in the M49 molecule, but is much less accessible relative to the other serotypes. Thus, the pepsin cleavage sites in the M protein correlate quite well with the boundaries of structurally distinct domains reflected by the predictive analysis. These sites apparently represent the flexible/hinge regions of the molecule. PepM49/a is the least repetitive and the shortest of the M protein pepsin fragments isolated so far. These results suggest that the flexibility of the interdomain regions in M protein may be dependent on the molecular size of their variable domains.(ABSTRACT TRUNCATED AT 400 WORDS)

Coregulation of type 12 M protein and streptococcal C5a peptidase genes in group A streptococci: evidence for a virulence regulon controlled by the virR locus

Group A streptococci express at least two surface-associated virulence factors, the antiphagocytic M protein and the antichemotactic streptococcal C5a peptidase (SCP). Preliminary evidence suggested that the biosynthesis of these two proteins is coordinately controlled and subject to simultaneous phase variation. To explore this possibility further, a series of phase-switching and phase-locked M- variants were assayed for SCP by enzyme-linked immunosorbent assay inhibition and for SCP-specific mRNA by dot blot hybridization. All M- cultures produced diminished amounts of SCP antigen and specific mRNA, whereas revertants produced quantities equivalent to those of the wild-type M+ culture. A phase-locked strain that harbors a deletion in a region upstream of the M12 and SCP genes, termed the virR locus, failed to produce SCP antigen or SCP-specific transcripts. The SCP-specific transcript produced by M+ bacteria was shown by Northern (RNA) blot hybridization to be 4 kilobases in size, distinguishing it from the transcript which encodes M protein. These data demonstrate that phase switching of both SCP and M12 proteins is at the transcriptional level and that expression is under the control of the upstream virR locus. We propose that the genetic determinants of these proteins and of colony morphology comprise a virulence regulon.