A group A streptococcal Enn protein potentially resulting from intergenomic recombination exhibits atypical immunoglobulin-binding characteristics

Molecular characterization of the interaction between human IgG and the M-related proteins from Streptococcus pyogenes

Group A Streptococcal M-related proteins (Mrps) are dimeric α-helical-coiled-coil cell membrane-bound surface proteins. During infection, Mrp recruit the fragment crystallizable region of human immunoglobulin G via their A-repeat regions to the bacterial surface, conferring upon the bacteria enhanced phagocytosis resistance and augmented growth in human blood. However, Mrps show a high degree of sequence diversity, and it is currently not known whether this diversity affects the Mrp-IgG interaction. Herein, we report that diverse Mrps all bind human IgG subclasses with nanomolar affinity, with differences in affinity which ranged from 3.7 to 11.1 nM for mixed IgG. Using surface plasmon resonance, we confirmed Mrps display preferential IgG-subclass binding. All Mrps were found to have a significantly weaker affinity for IgG3 (p < 0.05) compared to all other IgG subclasses. Furthermore, plasma pulldown assays analyzed via Western blotting revealed that all Mrp were able to bind IgG in the presence of other serum proteins at both 25 °C and 37 °C. Finally, we report that dimeric Mrps bind to IgG with a 1:1 stoichiometry, enhancing our understanding of this important host-pathogen interaction.

Streptococcus pyogenes genes that promote pharyngitis in primates

Streptococcus pyogenes (group A streptococcus; GAS) causes 600 million cases of pharyngitis annually worldwide. There is no licensed human GAS vaccine despite a century of research. Although the human oropharynx is the primary site of GAS infection, the pathogenic genes and molecular processes used to colonize, cause disease, and persist in the upper respiratory tract are poorly understood. Using dense transposon mutant libraries made with serotype M1 and M28 GAS strains and transposon-directed insertion sequencing, we performed genome-wide screens in the nonhuman primate (NHP) oropharynx. We identified many potentially novel GAS fitness genes, including a common set of 115 genes that contribute to fitness in both genetically distinct GAS strains during experimental NHP pharyngitis. Targeted deletion of 4 identified fitness genes/operons confirmed that our newly identified targets are critical for GAS virulence during experimental pharyngitis. Our screens discovered many surface-exposed or secreted proteins - substrates for vaccine research - that potentially contribute to GAS pharyngitis, including lipoprotein HitA. Pooled human immune globulin reacted with purified HitA, suggesting that humans produce antibodies against this lipoprotein. Our findings provide new information about GAS fitness in the upper respiratory tract that may assist in translational research, including developing novel vaccines.

Human MOSPD2: A bacterial Lmb mimicked auto-antigen is involved in immune infertility

Autoantibody production is one of the leading factors of immune infertility, an autoimmune disease of the male reproductive system. The potential involvement of MHC-class II derived self-peptides against bacterial proteins in the antisperm antibody (ASA) production has been reported previously. Apparently, Streptococcus agalactiae has been considered as an important pathogen to impart infection-induced infertility in a bacteriospermia associated leukocytospermia (LCS/BS) state. Hence, the present study attempts to confirm S. agalactiae specific Laminin binding protein (Lmb) derived self-peptide ('KDSYTKKAKAFKKEA') namely human Motile Sperm domain-containing protein 2 (MOSPD2) as an auto-antigen in LCS/BS condition. Semen samples were collected from infertile men with LCS/BS (n ​= ​17) and their fertile counterparts (n ​= ​10). Gram-positive bacteria were predominantly identified in the entire 17 LCS samples using culture method followed by 16S rDNA sequencing technique. TLRs 2 and 4 expression used as markers of immune response in spermatozoa and sperm dysfunction were elevated in the LCS/BS spermatozoa as compared to their fertile counterparts. A significant increase in oxidative stress indices i.e., protein carbonylation, lipid peroxidation and acridine orange test (AOT), was also observed in the LCS/BS spermatozoa. Spermatozoa lysate (both auto and heterologous), bacterial lysate (control) and synthesized MOSPD2 self-peptide were used to test their antigenicity against the autoantibodies by rocket immunoelectrophoresis (RIEP) assay. Seminal plasma from LCS/BS patients with S. agalactiae was used as the source of autoantibodies. Spermatozoa and bacteria lysate; and MOSPD2 self-peptide were able to bind autoantibodies in the seminal plasma. Besides, the self-peptide showed a dose dependent increase in the precipitation of antibody. T-cell epitope mapping of 48 Enterococcus faecalis and 91Staphylococcus aureus surface proteins confirmed MOSPD2 as a global auto-antigen. Thus, augmentation of TLR expression in LCS/BS spermatozoa inferred MOSPD2 to be a putative immunogen. Altogether, these findings will delineate the significance of MOSPD2 auto-antigen in a bacteria derived immune infertility condition.

Group A streptococcal M-like proteins: From pathogenesis to vaccine potential

M and M-like surface proteins from group A Streptococcus (GAS) act as virulence factors and have been used in multiple vaccine candidates. While the M protein has been extensively studied, the two genetically and functionally related M-like proteins, Mrp and Enn, although present in most streptococcal strains have been relatively less characterised. We compile the current state of knowledge for these two proteins, from discovery to recent studies on function and immunogenicity, using the M protein for comparison as a prototype of this family of proteins. We focus on the known interactions between M-like proteins and host ligand proteins, and analyse the genetic data supporting these interactions. We discuss known and possible functions of M-like proteins during GAS infections, and highlight knowledge gaps where further investigation is warranted.

Practical applications of high-affinity, albumin-binding proteins from a group G streptococcal isolate

Binding proteins that have high affinities for mammalian plasma proteins that are expressed on the surface of bacteria have proven valuable for the purification and detection of several biologically important molecules from human and animal plasma or serum. In this study, we have isolated a high affinity albumin-binding molecule from a group G streptococcal isolate of bovine origin and have demonstrated that the isolated protein can be biotinylated without loss of binding activity and can be used as a tracer for quantification of human serum albumin (HSA). The binding protein can be immobilized and used as a selective capture reagent in a competitive ELISA format using a biotinylated HSA tracer. In this assay format, the sensitivity of detection for 50% inhibition of binding of HSA was less than 1 microg/ml. When attached to the bacterial surface, this binding protein can be used to deplete albumin from human plasma, as analyzed by surface-enhanced laser desorption ionization time of flight mass spectrometry.

Streptococcus pyogenes sclB encodes a putative hypervariable surface protein with a collagen-like repetitive structure

Streptococcus pyogenes is the causative agent in a wide range of diseases of humans of varying severity. During a study scanning the genome sequence of a serotype M1 invasive isolate SF370 for novel surface proteins, an ORF, designated sclB, was identified. The putative protein encoded by sclB contains both a signal peptide and classic Gram-positive wall-associated sequences. Comparison of the sequences of this ORF with those from a number of unrelated isolates demonstrated that sclB encodes a putative surface protein with a variable N-terminal sequence followed by a variable length tract of collagen-like GXY(n) repeats. A further feature of sclB is the presence of CAAAA repeat tracts immediately downstream of the putative start codon. The number of these pentameric repeats varies from 4 to 15 between strains and variation in repeat number results in the predicted SclB protein being either in or out of frame relative to the start codon. These observations suggest that expression of this protein may be regulated at the translational level as a result of gain or loss of CAAAA repeats. While the function of SclB remains to be elucidated, an sclB-specific transcript was detected by RT-PCR during in vitro culture. Finally, it is shown that a second gene, sclA, potentially encoding a protein with a similar extensive collagen-like structure and variable N-terminal sequence, is present in all isolates of S. pyogenes tested to date. Thus S. pyogenes harbours a novel family of structurally related and surface-exposed proteins of potential importance in the pathogenic process.

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.

Absence of SpeB production in virulent large capsular forms of group A streptococcal strain 64

Passage in human blood of group A streptococcal isolate 64p was previously shown to result in the enhanced expression of M and M-related proteins. Similarly, when this isolate was injected into mice via an air sac model for skin infection, organisms recovered from the spleens showed both increased expression of M and M-related proteins and increased skin-invasive potential. We show that these phenotypic changes were not solely the result of increased transcription of the mRNAs encoding the M and M-related gene products. Rather, the altered expression was associated with posttranslational modifications of the M and M-related proteins that occur in this strain, based on the presence or absence of another virulence protein, the streptococcal cysteine protease SpeB. The phenotypic variability also correlates with colony size variation. Large colonies selected by both regimens expressed more hyaluronic acid, which may explain differences in colony morphology. All large-colony variants were SpeB negative and expressed three distinct immunoglobulin G (IgG)-binding proteins in the M and M-related protein family. Small-colony variants were SpeB positive and bound little IgG through their M and M-related proteins because these proteins, although made, were degraded or altered in profile by the SpeB protease. We conclude that passage in either human blood or a mouse selects for a stable, phase-varied strain of group A streptococci which is altered in many virulence properties.

Surface proteins of gram-positive bacteria and mechanisms of their targeting to the cell wall envelope

The cell wall envelope of gram-positive bacteria is a macromolecular, exoskeletal organelle that is assembled and turned over at designated sites. The cell wall also functions as a surface organelle that allows gram-positive pathogens to interact with their environment, in particular the tissues of the infected host. All of these functions require that surface proteins and enzymes be properly targeted to the cell wall envelope. Two basic mechanisms, cell wall sorting and targeting, have been identified. Cell well sorting is the covalent attachment of surface proteins to the peptidoglycan via a C-terminal sorting signal that contains a consensus LPXTG sequence. More than 100 proteins that possess cell wall-sorting signals, including the M proteins of Streptococcus pyogenes, protein A of Staphylococcus aureus, and several internalins of Listeria monocytogenes, have been identified. Cell wall targeting involves the noncovalent attachment of proteins to the cell surface via specialized binding domains. Several of these wall-binding domains appear to interact with secondary wall polymers that are associated with the peptidoglycan, for example teichoic acids and polysaccharides. Proteins that are targeted to the cell surface include muralytic enzymes such as autolysins, lysostaphin, and phage lytic enzymes. Other examples for targeted proteins are the surface S-layer proteins of bacilli and clostridia, as well as virulence factors required for the pathogenesis of L. monocytogenes (internalin B) and Streptococcus pneumoniae (PspA) infections. In this review we describe the mechanisms for both sorting and targeting of proteins to the envelope of gram-positive bacteria and review the functions of known surface proteins.

A globally disseminated M1 subclone of group A streptococci differs from other subclones by 70 kilobases of prophage DNA and capacity for high-frequency intracellular invasion

The M1inv+ subclone of M1 group A streptococci that spread globally in the late 1980s and early 1990s was previously identified by restriction fragment length polymorphism (RFLP), M protein, and SpeA exotoxin sequence analyses. Strains representing this subclone were characterized with regard to carriage of bacteriophage and capacity to invade cultured human epithelial cells. The M1inv+ subclone was found to harbor two entirely different prophages, phage T13 and phage T14, which together supplement its genome with nearly 70 kb of DNA. Phage T14 encodes the SpeA exotoxin and is closely related to the classic converting phage T12. Plaque-forming characteristics and RFLP analyses of phages T13 and T14 were compared to each other and to phage T12. Other subclones of M1, isolated in the 1970s to the early 1980s, lacked both prophages. The M1inv+ subclone was previously reported to be efficiently internalized by human epithelial cells. This potential was confirmed and expanded by comparing a variety of clinical isolates. The capacity for high-frequency invasion of epithelial cells was not transmitted to a laboratory strain of group A streptococci by the above-mentioned bacteriophages.

Identification of an insertion sequence located in a region encoding virulence factors of Streptococcus pyogenes

An insertion sequence, IS1562, was identified in a Streptococcus pyogenes strain of the clinically important M1 serotype. IS1562 is located in the mga regulon between the genes coding for the M protein and the C5a peptidase, both important virulence factors. The same or similar insertion sequences were found in most S. pyogenes strains, but the chromosomal location differed among isolates.

Expression of Two Different Antiphagocytic M Proteins by Streptococcus pyogenes of the OF+ Lineage

All clinical isolates of Streptococcus pyogenes (group A streptococcus) share the ability to resist phagocytosis and grow in human blood. In many strains, this property is due to the expression of a single antiphagocytic M protein, while other strains express more than one M-like molecule, of which the role in phagocytosis resistance is unclear. In particular, all S. pyogenes strains of the OF+ lineage, representing approximately half of all isolates, express two M-like proteins, Mrp and Emm, which are immunologically unrelated. These two proteins bind different ligands that have been implicated in phagocytosis resistance: Mrp binds fibrinogen and Emm binds the complement inhibitor C4BP. Using a clinical isolate of the common serotype 22, we created mutants affected in the mrp and emm genes and characterized them in phagocytosis experiments and by electron microscopy. A double mutant mrp−emm− showed strongly decreased resistance to phagocytosis, while mrp− and emm− single mutants grew well in blood. However, optimal growth required the expression of both Mrp and Emm. Experiments in which coagulation was inhibited using the specific thrombin inhibitor, hirudin, rather than heparin, indicated that Emm is more important than Mrp for resistance to phagocytosis. Tuftlike surface structures typical for S. pyogenes were still present in the mrp−emm− double mutant, but not in a mutant affected in the regulatory gene mga, indicating that the presence of these surface structures is not directly correlated to phagocytosis resistance. Our data imply that OF+ strains of S. pyogenes express two antiphagocytic M proteins with different ligand-binding properties.

Molecular markers for throat and skin isolates of group A streptococci

In summary, the emm chromosomal patterns distinguish between the two principal tissue site reservoirs of group A streptococci--the nasopharyngeal mucosa and impetigo lesion. Strains derived from normally sterile tissue sites are probably transmitted to new hosts by respiratory droplets, at least in the Connecticut population. The speA gene provides an example of how genetic exchange between different strains of group A streptococci may be limited to a single tissue site or to a subset of emm chromosomal patterns.

Two-domain motif for IgG-binding activity by group A streptococcal emm gene products

A biological role for the non-immune binding of human IgG by group A streptococci is evidenced by its strong association with a subpopulation of strains giving rise to tissue-specific infection. IgG-binding activity lies within many of the M and M-like surface proteins (encoded by emm genes), and several structurally distinct IgG-binding sites are known to exist. In this report, two adjacent IgG-binding domains, differing in their specificity for human IgG subclasses, are localized within the M-like protein, protein H. The putative coding regions for the two IgG-binding domains were mapped for 82 epidemiologically unrelated strains. Both coding regions are associated with phylogenetically distant emm genes, supporting a role for horizontal transfer and intergenomic recombination in the evolution of emm genes. In most instances, the two coding regions are tightly linked, suggesting that there exist strong selective pressures to maintain a two-domain binding motif. Both coding regions are found among all strains bearing emm gene markers associated with impetigo lesions as the principal tissue reservoir, but are absent from most strains that exhibit markers for a predominant nasopharyngeal reservoir. The data support the hypothesis that the pathogenic potential of an isolate is dictated, at least in part, by its unique array of multifunctional emm gene products.

Evidence for independent binding domains within a group A streptococcal type IIo IgG-binding protein

The gene for a type IIo IgG-binding protein has previously been cloned and sequenced. The approximately 60,000 M(r) recombinant gene product binds all four human IgG subclasses and fibrinogen. Treatment of this recombinant protein with CNBr results in generation of a series of fragments. One fragment, an approximately 32,000 M(r) polypeptide, binds IgG1, IgG2, and IgG4 but neither IgG3 nor fibrinogen. N-terminal amino sequencing of this fragment indicated that this was an internal fragment of the protein starting at amino acid 186 of the mature protein. These findings provide evidence for two distinct domains for binding IgG1, IgG2, and IgG4 and binding IgG3 within a single bacterial IgG-binding protein.

A new type of cohesin domain that specifically binds the dockerin domain of the Clostridium thermocellum cellulosome-integrating protein CipA

The cellulosome-integrating protein CipA, which serves as a scaffolding protein for the cellulolytic complex produced by Clostridium thermocellum, comprises a COOH-terminal duplicated segment termed the dockerin domain. This paper reports the cloning and sequencing of a gene, termed sdbA (for scaffoldin dockerin binding), encoding a protein which specifically binds the dockerin domain of CipA. The sequenced fragment comprises an open reading frame of 1,893 nucleotides encoding a 631-amino-acid polypeptide, termed SdbA, with a calculated molecular mass of 68,577 kDa. SAA comprises an NH2-terminal leader peptide followed by three distinct regions. The NH2-terminal region is similar to the NH2-terminal repeats of C. thermocellum OlpB and ORF2p. The central region is rich in lysine and harbors a motif present in Streptococcus M proteins. The COOH-terminal region consists of a triplicated sequence present in several bacterial cell surface proteins. The NH2-terminal region of SdbA and a fusion protein carrying the first NH2-terminal repeat of OlpB were shown to bind the dockerin domain of CipA. Thus, a new type of cohesin domain, which is present in one, two, and four copies in SdbA, ORF2p, and OlpB, respectively, can be defined. Since OlpB and most likely SdbA and ORF2p are located in the cell envelope, the three proteins probably participate in anchoring CipA (and the cellulosome) to the cell surface.

Identification of an amino acid signature sequence predictive of protein G-inhibitable IgG3-binding activity in group-A streptococcal IgG-binding proteins

Sequence comparison of six known group-A streptococcal IgG-binding proteins, sharing the common property of protein G-inhibitable IgG3-binding-activity, identified a highly conserved 35-amino-acid (aa) sequence (74-100% similarity) within an EQ-rich central conserved core region of each protein. A search of aa sequence databases identified four additional proteins with > 50% similarity to this consensus sequence. All of these proteins demonstrated protein G-inhibitable IgG3-binding activity. Taken together, these results identify a signature sequence that predicts the presence of a protein G-inhibitable IgG3-binding domain(s) in group-A streptococcal IgG-binding proteins.

Structure of a group C streptococcal protein that binds to fibrinogen, albumin and immunoglobulin G via overlapping modules

Pathogenic streptococci express surface proteins that bind to host serum proteins. A novel multiple-ligand-binding protein has now been identified in a species belonging to serotype C streptococci. This protein binds to fibrinogen, albumin and IgG and was therefore designated FAI protein. The structure of the fai gene has been determined, and deletion analysis and expression of FAI fusion polypeptides revealed that the binding domain for fibrinogen and IgG is located within the nonrepetitive N-terminal half of the protein. A 93-amino acid peptide retained the ability to bind both proteins, whereas a 56-amino acid subpeptide only bound fibrinogen. IgG-binding activity required the complete fibrinogen-binding domain and an additional 37 amino acids C-terminal to it, and albumin-binding activity was only obtained with a polypeptide reflecting the complete surface-exposed region of FAI protein indicating that the binding sites for each ligand were located on overlapping modules. Signal sequence, C repeat region and C-terminus revealed high homology to group A streptococcal M proteins whereas the N-terminal region containing the fibrinogen/IgG-binding domains is completely different and exhibits no similarity to any other previously characterized protein. Thus FAI protein exhibits a framework structure that might have evolved in group C streptococci via fusion of unrelated sequences, thereby generating an albumin-binding domain in the functional context of multiple-ligand-binding activity.

Characterization of a type II'o group A streptococcal immunoglobulin-binding protein

The opacity factor positive M type 2 group A streptococcal isolate, A207, expresses a unique functional type II'o IgG-binding protein which reacts with all four human IgG subclasses and rabbit IgG. In order to determine the gene product or products responsible for this activity, three genes of the vir regulon from this isolate were cloned, expressed and analysed. The fcr A2 gene coded for a protein binding hyman IgG1, IgG2 and IgG4 but not IgG3. The enn2 gene coded for a protein reacting exclusively with human IgA, while the emmL2 gene product bound IgG1, IgG2, IgG3 and IgG4 as well as rabbit but not horse or pig IgG. The IgG3-binding activity of the EmmL2 protein was functionally indistinguishable from the Form 1 IgG3-binding activity present in heat extracts of group A isolate A207.

Characterization of a gene coding for a type IIo bacterial IgG-binding protein

Two antigenic classes of non-immune IgG-binding proteins can be expressed by group A streptococci. One antigenic group of proteins is recognized by an antibody prepared against the product of a cloned fcrA gene (anti-FcRA). In this study, the immunogen used to prepare the antibody that defines the second antigenic class was shown to be the product of the emm-like (emmL) gene of M serotype 55 group A isolate, A928. The emmL55 gene expressed in E. coli produced an M(r) approximately 58,000 molecule which bound human IgG1, IgG2, IgG3 and IgG4, as well as horse, rabbit and pig IgG in a non-immune fashion. These properties are characteristic of the previously described type IIo IgG-binding protein isolated from this strain. In addition, the recombinant protein was reactive with human serum albumin and fibrinogen. The emmL 55 gene sequence was analysed and found to have the organization and sequence characteristics of a typical class I emm-like gene.

Molecular population genetic analysis of the enn subdivision of group A streptococcal emm-like genes: horizontal gene transfer and restricted variation among enn genes

The group A streptococcal emm-like genes, which encode the cell-surface M and M-like proteins, are divided into distinct mrp, emm and enn subdivisions and are clustered together in a region of the chromosome called the vir regulon. In order to understand the mechanisms involved in the evolution of emm-like genes, a 180 bp fragment of the 5' variable region of the enn gene was characterized in 31 strains for which emm sequences and multilocus enzyme electrophoretic profiles have been previously determined. The results demonstrate that nucleotide polymorphisms at the enn locus are generated predominantly by point mutations and short deletions or insertions, and that variation among enn and emm genes has arisen by similar mechanisms. However, diversity at the enn locus is restricted in comparison to the emm locus. Moreover, there is strong evidence for intragenic recombination at the enn locus and the pattern of distribution of emm and enn alleles among strains suggests that these genes may be independently acquired by horizontal transfer and recombination from distinct donor strains, thereby generating a mosaic structure for the vir regulon. The results add to a growing body of evidence that horizontal gene transfer has played a major role in the evolution of Streptococcus pyogenes vir regulons.

M or M-like protein gene polymorphisms in human group G streptococci

Many group G streptococci (GGS) isolated from infected humans (but not from animal sources) express M or M-like proteins with biological, immunochemical, and genetic features similar to those of group A streptococci (GAS). To further elucidate the recently proposed M-like protein gene (emmL gene) polymorphisms in GGS, Southern blots of genomic DNAs from 38 epidemiologically unrelated GGS strains isolated from human specimens and 12 GGS strains recovered from animal sources were hybridized with oligonucleotide probes designed to specifically detect GAS M class I and M class II M protein (emm) genes. All human-associated GGS strains showed DNA homology to the GAS M class I emm gene probe, whereas no hybridization was found with DNA from any of the animal-associated strains. The emmL genes from all human isolates were amplified by PCR, and the complete sequence of the emmL gene of the Rebecca Lancefield grouping strain D166B was determined. Again, this gene exhibited the structural features typical for emm genes of M class I GAS. The 5' regions of the PCR-amplified emmL genes of the remaining 37 human GGS strains were sequenced. This region showed a sequence diversity similar to that known for GAS emm genes. When strains whose N-terminal emmL gene sequences showed a homology of > 95% were defined as belonging to one genetic type, 30 strains were segregated into six distinct genetic types, whereas the remaining 8 strains each exhibited a unique emmL gene sequence. A high degree of homology between the N-terminal emmL gene segments of six GGS strains and the corresponding regions of either the emm12 or the emm57 gene of GAS was found, suggesting a horizontal gene transfer between strains of these species of beta-hemolytic streptococci. Besides a further understanding of the evolution of GGS emmL genes, the observed emmL gene polymorphisms in GGS could provide the basis for a molecular subspecies delineation of strains and offers the potential of typing GGS for epidemiological purposes.

The group A streptococcal virR49 gene controls expression of four structural vir regulon genes

Within a genomic locus termed the vir regulon, virR genes of opacity factor-nonproducing (OF-) group A streptococci (GAS) are known to control the expression of the genes encoding M protein (emm) and C5a peptidase (scpA) and of virR itself. Within the corresponding genomic locus, opacity factor-producing (OF+) GAS harbor additional emm-related genes encoding immunoglobulin G- and immunoglobulin A-binding proteins (fcrA and enn, respectively). The virR gene region of the OF+ GAS M-type 49 strain CS101 was amplified by PCR, and 2,650 bp were directly sequenced. An open reading frame of 1,599 bp exhibited 76% overall homology to published virR sequences. By utilizing mRNA analysis, the 5' ends of two specific transcripts were mapped 370 and 174 bp upstream of the start codon of this open reading frame. The deduced sequences of the corresponding promoters and their locations differed from those of previously reported virR promoters. Transcripts from wild-type fcrA49, emm49, enn49, and scpA49 genes located downstream of virR49 were characterized as being monocistronic. The transcripts were quantified and mapped for their 5' ends. Subsequently, the virR49 gene was inactivated by specific insertion of a nonreplicative pSF152 vector containing recombinant virR49 sequences. The RNA from the resulting vir-mut strain did not contain transcripts of virR49, fcrA49, emm49, or enn49 and contained reduced amounts of the scpA49 transcript when compared with wild-type RNA. The mRNA control from the streptokinase gene was demonstrated not to be affected. When strain vir-mut was rotated in human blood, it was found to be fully sensitive to phagocytosis by human leukocytes. Thus, the present study provides evidence that virR genes in OF+ GAS could be involved in the control of up to five vir regulon genes, and their unaffected regulatory activity is associated with features postulated as crucial for GAS virulence.

Non-congruent relationships between variation in emm gene sequences and the population genetic structure of group A streptococci

To examine the molecular population genetics of the M protein family of Streptococcus pyogenes (group A Streptococcus), the 5' regions of polymerase chain reaction-amplified emm products from 79 M serotypes were sequenced and the phylogeny was compared to estimates of overall genetic relationships among strains determined by multilocus enzyme electrophoresis. Although the 5' emm sequences from several strains designated as distinct M types were identical or almost identical, the overall pattern is characterized by very extensive variation. The composition of distinct emm sequence clusters generally parallels the ability of strains to express serum opacity factor and in some cases historical associations of certain M types with acute rheumatic fever, but not with M types classified as nephritogenic. For many strains there is a lack of congruency between variation in 5' emm sequences and estimates of overall chromosomal relationships, which is undoubtedly due to horizontal transfer and recombination of emm sequences. The results of these studies provide insights into the nature and extent of emm sequence variation and describe how this variation 'maps' onto the population genetic structure of extant S. pyogenes lineages. The complexity of emm sequence and streptococcal cell lineage relationships revealed by this analysis has significant implications for understanding evolutionary events generating strain diversity and the epidemiology of S. pyogenes diseases.

Genetic variability of the emm-related gene of the large vir regulon of group A streptococci: potential intra- and intergenomic recombination events

One of the most prevalent genetic lineages of group A streptococci (GAS) harbors a genomic locus termed the large vir regulon, which contains an emm gene encoding the antiphagocytic M protein, and structurally related fcrA and enn (emm-related) genes encoding immunoglobulin-binding proteins. In the present study more than 100 large vir regulons from 42 different GAS serotypes were analyzed by PCR and partial DNA sequencing. On comparing these data to published sequences, sites of mutational and putative recombinational events were identified and ordered with respect to their intra/intergenic or intra/intergenomic nature. The emm-related genes were found to display small intragenic deletions or insertions, were completely deleted from, or newly inserted into the genome, or were fused to adjacent genes. Intergenomic exchanges of complete emm-related genes, or segments thereof, between different vir regulons were detected. Most of these processes seem to involve short flanking direct repeats. Occasionally, the structural changes could be correlated with changes in the functions of the encoded proteins.