Identification and immunogenicity of group A Streptococcus culture supernatant proteins

Differential substrate preferences IN ACTINOBACTERIAL protein O-MANNOSYLTRANSFERASES and alteration of protein-O-MANNOSYLATION by choice of secretion pathway

Protein-O-mannosylation (POM) is a form of O-glycosylation that is ubiquitous and has been studied extensively throughout in fungi and animals. The key glycosyltransferase, protein O-mannosyltransferase (PMT), a member of family GT-39, is also found in over 3,800 bacterial genomes but has only been minimally examined from prokaryotes. In prokaryotes POM has only been investigated in terms of pathogenicity (in Mycobacterium tuberculosis) even though there are far more non-pathogenic bacteria that appear to carry out POM. To date, there is no consensus on what benefit POM imparts to the non-pathogenic bacteria that can perform it. Through the generation of a POM deficient mutant of Corynebacterium glutamicum - a widely utilized and known protein O-mannosylating actinobacteria - this work shows that even closely related actinobacterial GT-39 s (the enzymes responsible for the initiation of POM) can have different substrate specificities for targets of POM. Moreover, presented here is evidence that POM does not only occur in a SEC-dependent manner; POM also occurs with TAT and non-SEC secreted substrates in a specific and likely tightly regulated manner. Together these results highlight the need for further biochemical characterization of POM in these and other bacterial species to help elucidate the true nature of its biological functions.

Bacterial nucleoid-associated protein HU as an extracellular player in host-pathogen interaction

HU protein is a member of nucleoid-associated proteins (NAPs) and is an important regulator of bacterial virulence, pathogenesis and survival. NAPs are mainly DNA structuring proteins that influence several molecular processes by binding the DNA. HU´s indispensable role in DNA-related processes in bacteria was described. HU protein is a necessary bacterial transcription factor and is considered to be a virulence determinant as well. Less is known about its direct role in host-pathogen interactions. The latest studies suggest that HU protein may be secreted outside bacteria and be a part of the extracellular matrix. Moreover, HU protein can be internalized in a host cell after bacterial infection. Its role in the host cell is not well described and further studies are extremely needed. Existing results suggest the involvement of HU protein in host cell immune response modulation in bacterial favor, which can help pathogens resist host defense mechanisms. A better understanding of the HU protein’s role in the host cell will help to effective treatment development.

The Role of Streptococcal Cell-Envelope Proteases in Bacterial Evasion of the Innate Immune System

Bacteria possess the ability to evolve varied and ingenious strategies to outwit the host immune system, instigating an evolutionary arms race. Proteases are amongst the many weapons employed by bacteria, which specifically cleave and neutralize key signalling molecules required for a coordinated immune response. In this article, we focus on a family of S8 subtilisin-like serine proteases expressed as cell-envelope proteases (CEPs) by group A and group B streptococci. Two of these proteases known as Streptococcus pyogenes CEP (SpyCEP) and C5a peptidase cleave the chemokine CXCL8 and the complement fragment C5a, respectively. Both CXCL8 and C5a are potent neutrophil-recruiting chemokines, and by neutralizing their activity, streptococci evade a key defence mechanism of innate immunity. We review the mechanisms by which CXCL8 and C5a recruit neutrophils and the characterization of SpyCEP and C5a peptidase, including both in vitro and in vivo studies. Recently described structural insights into the function of this CEP family are also discussed. We conclude by examining the progress of prototypic vaccines incorporating SpyCEP and C5a peptidase in their preparation. Since streptococci-producing SpyCEP and C5a peptidase are responsible for a considerable global disease burden, targeting these proteases by vaccination strategies or by small-molecule antagonists should provide protection from and promote the resolution of streptococcal infections.

Multifunctional Fructose 1,6-Bisphosphate Aldolase as a Therapeutic Target

Fructose 1,6-bisphosphate aldolase is a ubiquitous cytosolic enzyme that catalyzes the fourth step of glycolysis. Aldolases are classified into three groups: Class-I, Class-IA, and Class-II; all classes share similar structural features but low amino acid identity. Apart from their conserved role in carbohydrate metabolism, aldolases have been reported to perform numerous non-enzymatic functions. Here we review the myriad "moonlighting" functions of this classical enzyme, many of which are centered on its ability to bind to an array of partner proteins that impact cellular scaffolding, signaling, transcription, and motility. In addition to the cytosolic location, aldolase has been found the extracellular surface of several pathogenic bacteria, fungi, protozoans, and metazoans. In the extracellular space, the enzyme has been reported to perform virulence-enhancing moonlighting functions e.g., plasminogen binding, host cell adhesion, and immunomodulation. Aldolase's importance has made it both a drug target and vaccine candidate. In this review, we note the several inhibitors that have been synthesized with high specificity for the aldolases of pathogens and cancer cells and have been shown to inhibit classical enzyme activity and moonlighting functions. We also review the many trials in which recombinant aldolases have been used as vaccine targets against a wide variety of pathogenic organisms including bacteria, fungi, and metazoan parasites. Most of such trials generated significant protection from challenge infection, correlated with antigen-specific cellular and humoral immune responses. We argue that refinement of aldolase antigen preparations and expansion of immunization trials should be encouraged to promote the advancement of promising, protective aldolase vaccines.

Protocol for Proteome Analysis of Group A Streptococcus

This chapter describes a protocol for the separation of different cell fractions from Streptococcus pyogenes and sample preparation for analysis by mass spectrometry. The presented approach can be used for the analysis of all subcellular proteomes from S. pyogenes and enables identification of drug or vaccine targets within a certain cellular fraction. Here, proteins integral to the plasma membrane are of particular interest for the development of new antimicrobial therapies.

Bifidobacteria cell wall-derived exo-polysaccharides, lipoteichoic acids, peptidoglycans, polar lipids and proteins - their chemical structure and biological attributes

A variety of health benefits has been documented to be associated with the consumption of probiotic bacteria, namely bifidobacteria and lactobacilli. Thanks to the scientific advances in recent years we are beginning to understand the molecular mechanisms by which bacteria in general and probiotic bacteria in particular act as host physiology and immune system modulators. More recently, the focus has shifted from live bacteria towards bacteria-derived defined molecules, so called postbiotics. These molecules may represent safer alternative compared to the live bacteria while retaining the desired effects on the host. The excellent source of effector macromolecules is the bacterial envelope. It contains compounds that are pivotal in the adhesion phenomenon, provide direct bacteria-to-host signaling capacity and the associated physiological impact and immunomodulatory properties of bacteria. Here we comprehensively review the structure and biological role of Bifidobacterium surface and cell wall molecules: exopolysaccharides, cell wall polysaccharides, lipoteichoic acids, polar lipids, peptidoglycans and proteins. We discuss their involvement in direct signaling to the host cells and their described immunomodulatory effects.

Tissue Tropism in Streptococcal Infection: Wild-Type M1T1 Group A Streptococcus Is Efficiently Cleared by Neutrophils Using an NADPH Oxidase-Dependent Mechanism in the Lung but Not in the Skin

Group A Streptococcus (GAS) commonly causes pharyngitis and skin infections. Little is known why streptococcal pharyngitis usually does not lead to pneumonia and why the skin is a favorite niche for GAS. To partially address these questions, the effectiveness of neutrophils in clearing wild-type (wt) M1T1 GAS strain MGAS2221 from the lung and from the skin was examined in murine models of intratracheal pneumonia and subcutaneous infection. Ninety-nine point seven percent of the MGAS2221 inoculum was cleared from the lungs of C57BL/6J mice at 24 h after inoculation, while there was no MGAS2221 clearance from skin infection sites. The bronchial termini had robust neutrophil infiltration, and depletion of neutrophils abolished MGAS2221 clearance from the lung. Phagocyte NADPH oxidase but not myeloperoxidase was required for MGAS2221 clearance. Thus, wt M1T1 GAS can be cleared by neutrophils using an NADPH oxidase-dependent mechanism in the lung. MGAS2221 induced robust neutrophil infiltration at the edge of skin infection sites and throughout infection sites at 24 h and 48 h after inoculation, respectively. Neutrophils within MGAS2221 infection sites had no nuclear staining. Skin infection sites of streptolysin S-deficient MGAS2221 ΔsagA were full of neutrophils with nuclear staining, whereas MGAS2221 ΔsagA infection was not cleared. Gp91^phox knockout (KO) and control mice had similar GAS numbers at skin infection sites and similar abilities to select SpeB activity-negative (SpeB^A-) variants. These results indicate that phagocyte NADPH oxidase-mediated GAS killing is compromised in the skin. Our findings support a model for GAS skin tropism in which GAS generates an anoxic niche to evade phagocyte NADPH oxidase-mediated clearance.

Comprehensive Mass Spectrometric Survey of Streptococcus pyogenes Subcellular Proteomes

Streptococcus pyogenes is a major global health burden causing a wide variety of diseases. Because a vaccine against this bacterium is still lacking, vaccine candidates or antimicrobial therapies are urgently needed. Here we use an invasive and clinically relevant streptococcal M1 serotype to characterize the bacterial proteome in-depth. An elaborate fractionation technique is employed to separate the different cell fractions, followed by shotgun mass-spectrometry analysis, allowing us to confirm the expression of nearly two-thirds (1022) of the 1690 open reading frames predicted for the streptococcal M1 reference proteome. In contrast with other studies, we present the entire isolated membrane proteome, which opens up a whole new source for drug targets. We show both the unique and most prevalent proteins for each cellular fraction and analyze the presence of predicted cell-wall-anchored proteins and lipoproteins. With our approach, we also identify a variety of novel proteins whose presence has not been reported in previous proteome studies. Proteins of interest, potential virulence factors, and drug or vaccine targets are discussed for each cellular fraction. Overall, the results of this work represent the so-far widest proteomic approach to characterize the protein composition and localization in S. pyogenes.

Null Mutations of Group A Streptococcus Orphan Kinase RocA: Selection in Mouse Infection and Comparison with CovS Mutations in Alteration of In Vitro and In Vivo Protease SpeB Expression and Virulence

Group A Streptococcus (GAS) acquires mutations of the virulence regulator CovRS in human and mouse infections, and these mutations result in the upregulation of virulence genes and the downregulation of the protease SpeB. To identify in vivo mutants with novel phenotypes, GAS isolates from infected mice were screened by enzymatic assays for SpeB and the platelet-activating factor acetylhydrolase Sse, and a new type of variant that had enhanced Sse expression and normal levels of SpeB production was identified (the variants had a phenotype referred to as enhanced Sse activity [Sse^A+] and normal SpeB activity [SpeB^A+]). Sse^A+ SpeB^A+ variants had transcript levels of CovRS-controlled virulence genes comparable to those of a covS mutant but had no covRS mutations. Genome resequencing of an Sse^A+ SpeB^A+ isolate identified a C605A nonsense mutation in orphan kinase gene rocA, and 6 other Sse^A+ SpeB^A+ isolates also had nonsense mutations or small indels in rocA RocA and CovS mutants had similar levels of enhancement of the expression of CovRS-controlled virulence genes at the exponential growth phase; however, mutations of RocA but not mutations of CovS did not result in the downregulation of speB transcription at stationary growth phase or in subcutaneous infection of mice. GAS with RocA and CovS mutations caused greater enhancement of the expression of hasA than spyCEP in mouse skin infection than wild-type GAS did. RocA mutants ranked between wild-type GAS and CovS mutants in skin invasion, inhibition of neutrophil recruitment, and virulence in subcutaneous infection of mice. Thus, GAS RocA mutants can be selected in subcutaneous infections in mice and exhibit gene expression patterns and virulences distinct from those of CovS mutants. The findings provide novel information for understanding GAS fitness mutations in vivo, virulence gene regulation, in vivo gene expression, and virulence.

A Two-Component Regulatory System Impacts Extracellular Membrane-Derived Vesicle Production in Group A Streptococcus

Export of macromolecules via extracellular membrane-derived vesicles (MVs) plays an important role in the biology of Gram-negative bacteria. Gram-positive bacteria have also recently been reported to produce MVs; however, the composition and mechanisms governing vesiculogenesis in Gram-positive bacteria remain undefined. Here, we describe MV production in the Gram-positive human pathogen group A streptococcus (GAS), the etiological agent of necrotizing fasciitis and streptococcal toxic shock syndrome. M1 serotype GAS isolates in culture exhibit MV structures both on the cell wall surface and in the near vicinity of bacterial cells. A comprehensive analysis of MV proteins identified both virulence-associated protein substrates of the general secretory pathway in addition to "anchorless surface proteins." Characteristic differences in the contents, distributions, and fatty acid compositions of specific lipids between MVs and GAS cell membrane were also observed. Furthermore, deep RNA sequencing of vesicular RNAs revealed that GAS MVs contained differentially abundant RNA species relative to bacterial cellular RNA. MV production by GAS strains varied in a manner dependent on an intact two-component system, CovRS, with MV production negatively regulated by the system. Modulation of MV production through CovRS was found to be independent of both GAS cysteine protease SpeB and capsule biosynthesis. Our data provide an explanation for GAS secretion of macromolecules, including RNAs, lipids, and proteins, and illustrate a regulatory mechanism coordinating this secretory response.

IMPORTANCE

Group A streptococcus (GAS) is a Gram-positive bacterial pathogen responsible for more than 500,000 deaths annually. Establishment of GAS infection is dependent on a suite of proteins exported via the general secretory pathway. Here, we show that GAS naturally produces extracellular vesicles with a unique lipid composition that are laden with proteins and RNAs. Interestingly, both virulence-associated proteins and RNA species were found to be differentially abundant in vesicles relative to the bacteria. Furthermore, we show that genetic disruption of the virulence-associated two-component regulator CovRS leads to an increase in vesicle production. This study comprehensively describes the protein, RNA, and lipid composition of GAS-secreted MVs and alludes to a regulatory system impacting this process.

Identification of surface-associated proteins of Bifidobacterium animalis ssp. lactis KLDS 2.0603 by enzymatic shaving

Bifidobacteria are commensal microorganisms of the human and animal intestinal tract, and their surface proteins can mediate bacterial communication and chemical sensing in the environment, as well as facilitate interactions between bacteria and the host. However, a systematic study of the outer surface-associated proteome of bifidobacteria has not been undertaken. In the present study, the proteins located on the surface of Bifidobacterium animalis ssp. lactis KLDS 2.0603 were systematically identified by a nongel proteomic approach, which consisted of the shaving of the bacterial surface with trypsin and an analysis of the released peptides by liquid chromatography-tandem mass spectrometry. A total of 105 surface-associated proteins were found, of which 15 proteins could potentially be involved in adhesion and interactions between bifidobacteria and the host. The proteins related to adhesion and interaction between bacteria and the host include pilus structure proteins (Fim A, Fim B), 10 moonlighting proteins, an NLP/P60 family protein, an immunogenic secreted protein, and a putative sugar-binding secreted protein. The results provide the basis for future studies on the molecular mechanisms of the interactions between bifidobacteria and the host.

Expression and immunological characteristics of the surface-localized pyruvate kinase in Mycoplasma gallisepticum

The widespread avian pathogen Mycoplasma gallisepticum is a causative agent of respiratory disease. The wall-less prokaryotes lack some tricarboxylic acid cycle enzymes, therefore, the glycolysis metabolic pathway is of great importance to these organisms. Pyruvate kinase (PK) is one of the key enzymes of the glycolytic pathway, and its immunological characteristics in Mycoplasma are not well known. In this study, the M. gallisepticum pyruvate kinase fusion protein (PykF) was expressed in a pET system. The full-length of the gene was subcloned into the expression vector pET28a(+) to construct the pET28a-rMGPykF plasmid, which was then transformed into Escherichia coli strain BL21 (DE3) cells. The expression of the 62 kDa recombinant protein of rMGPykF in E. coli strain BL21 (DE3) was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Coomassie blue staining. Purified rMGPykF exhibited PK catalytic activity, which could reflect the conversion of NADH to NAD(+). Mouse anti-PykF antibodies were generated by immunization of mice with rMGPykF. Immunoblot and immunoelectron microscopy assays identified PykF as an immunogenic protein expressed on the surface of M. gallisepticum cells. Bactericidal assay showed that anti-rMGPykF antiserum killed 70.55% of M. gallisepticum cells, suggesting the protective potential of PykF. Adherence inhibition assay on immortalized chicken fibroblasts (DF-1) cells revealed more than 39.31% inhibition of adhesion in the presence of anti-rMGPykF antiserum, suggesting that PykF of M. gallisepticum participates in bacterial adhesion to DF-1 cells.

Lactic acid bacterial symbionts in honeybees - an unknown key to honey's antimicrobial and therapeutic activities

Could honeybees' most valuable contribution to mankind besides pollination services be alternative tools against infections? Today, due to the emerging antibiotic-resistant pathogens, we are facing a new era of searching for alternative tools against infections. Natural products such as honey have been applied against human's infections for millennia without sufficient scientific evidence. A unique lactic acid bacterial (LAB) microbiota was discovered by us, which is in symbiosis with honeybees and present in large amounts in fresh honey across the world. This work investigates if the LAB symbionts are the source to the unknown factors contributing to honey's properties. Hence, we tested the LAB against severe wound pathogens such as methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and vancomycin-resistant Enterococcus (VRE) among others. We demonstrate a strong antimicrobial activity from each symbiont and a synergistic effect, which counteracted all the tested pathogens. The mechanisms of action are partly shown by elucidating the production of active compounds such as proteins, fatty acids, anaesthetics, organic acids, volatiles and hydrogen peroxide. We show that the symbionts produce a myriad of active compounds that remain in variable amounts in mature honey. Further studies are now required to investigate if these symbionts have a potential in clinical applications as alternative tools against topical human and animal infections.

Functional and structural properties of a novel protein and virulence factor (Protein sHIP) in Streptococcus pyogenes

Streptococcus pyogenes is a significant bacterial pathogen in the human population. The importance of virulence factors for the survival and colonization of S. pyogenes is well established, and many of these factors are exposed to the extracellular environment, enabling bacterial interactions with the host. In the present study, we quantitatively analyzed and compared S. pyogenes proteins in the growth medium of a strain that is virulent to mice with a non-virulent strain. Particularly, one of these proteins was present at significantly higher levels in stationary growth medium from the virulent strain. We determined the three-dimensional structure of the protein that showed a unique tetrameric organization composed of four helix-loop-helix motifs. Affinity pull-down mass spectrometry analysis in human plasma demonstrated that the protein interacts with histidine-rich glycoprotein (HRG), and the name sHIP (streptococcal histidine-rich glycoprotein-interacting protein) is therefore proposed. HRG has antibacterial activity, and when challenged by HRG, sHIP was found to rescue S. pyogenes bacteria. This and the finding that patients with invasive S. pyogenes infection respond with antibody production against sHIP suggest a role for the protein in S. pyogenes pathogenesis.

Surface proteins of group G Streptococcus in different phases of growth: patterns of production and implications for the host-bacteria relationship

Group G Streptococcus (GGS) is a human bacterial pathogen expressing surface proteins FOG and protein G (PG) which interact with several host defence systems, including the complement and contact systems. Selected reaction monitoring mass spectrometry, electron microscopy and protein binding assays were used to track the amounts of FOG and PG intracellularly and on the bacterial surface during different phases of growth. Large and increasing amounts of PG were present on the surface in the stationary growth phase, and this was due to de novo production. In contrast, the amount of FOG did not change substantially during this phase. Apart from PG, a number of housekeeping proteins also increased in abundance in the stationary phase. These results show that GGS protein production is active during the stationary phase and that the bacteria actively remodel their surface and enter a less pro-inflammatory state in this phase.

Proteins of novel lactic acid bacteria from Apis mellifera mellifera: an insight into the production of known extra-cellular proteins during microbial stress

BACKGROUND

Lactic acid bacteria (LAB) has been considered a beneficial bacterial group, found as part of the microbiota of diverse hosts, including humans and various animals. However, the mechanisms of how hosts and LAB interact are still poorly understood. Previous work demonstrates that 13 species of Lactobacillus and Bifidobacterium from the honey crop in bees function symbiotically with the honeybee. They protect each other, their hosts, and the surrounding environment against severe bee pathogens, bacteria, and yeasts. Therefore, we hypothesized that these LAB under stress, i.e. in their natural niche in the honey crop, are likely to produce bioactive substances with antimicrobial activity.

RESULTS

The genomic analysis of the LAB demonstrated varying genome sizes ranging from 1.5 to 2.2 mega-base pairs (Mbps) which points out a clear difference within the protein gene content, as well as specialized functions in the honeybee microbiota and their adaptation to their host. We demonstrate a clear variation between the secreted proteins of the symbiotic LAB when subjected to microbial stressors. We have identified that 10 of the 13 LAB produced extra-cellular proteins of known or unknown function in which some are arranged in interesting putative operons that may be involved in antimicrobial action, host interaction, or biofilm formation. The most common known extra-cellular proteins secreted were enzymes, DNA chaperones, S-layer proteins, bacteriocins, and lysozymes. A new bacteriocin may have been identified in one of the LAB symbionts while many proteins with unknown functions were produced which must be investigated further.

CONCLUSIONS

The 13 LAB symbionts likely play different roles in their natural environment defending their niche and their host and participating in the honeybee's food production. These roles are partly played through producing extracellular proteins on exposure to microbial stressors widely found in natural occurring flowers. Many of these secreted proteins may have a putative antimicrobial function. In the future, understanding these processes in this complicated environment may lead to novel applications of honey crop LAB proteins.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of SpyCEP, a candidate antigen for a vaccine against Streptococcus pyogenes

Streptococcus pyogenes (Group A streptococcus; GAS) is an important human pathogen against which an effective vaccine does not yet exist. The S. pyogenes protein SpyCEP (S. pyogenes cell-envelope proteinase) is a surface-exposed subtilisin-like serine protease of 1647 amino acids. In addition to its auto-protease activity, SpyCEP is capable of cleaving interleukin 8 and related chemokines, contributing to GAS immune-evasion strategies. SpyCEP is immunogenic and confers protection in animal models of GAS infections. In order to structurally characterize this promising vaccine candidate, several SpyCEP protein-expression constructs were designed, cloned, produced in Escherichia coli, purified by affinity chromatography and subjected to crystallization trials. Crystals of a selenomethionyl form of a near-full-length SpyCEP ectodomain were obtained. The crystals diffracted X-rays to 3.3 Å resolution and belonged to space group C2, with unit-cell parameters a=139.2, b=120.4, c=104.3 Å, β=111°.

Extracellular proteome analysis of Leptospira interrogans serovar Lai

Abstract Leptospirosis is one of the most important zoonoses. Leptospira interrogans serovar Lai is a pathogenic spirochete that is responsible for leptospirosis. Extracellular proteins play an important role in the pathogenicity of this bacterium. In this study, L. interrogans serovar Lai was grown in protein-free medium; the supernatant was collected and subsequently analyzed as the extracellular proteome. A total of 66 proteins with more than two unique peptides were detected by MS/MS, and 33 of these were predicted to be extracellular proteins by a combination of bioinformatics analyses, including Psortb, cello, SoSuiGramN and SignalP. Comparisons of the transcriptional levels of these 33 genes between in vivo and in vitro conditions revealed that 15 genes were upregulated and two genes were downregulated in vivo compared to in vitro. A BLAST search for the components of secretion system at the genomic and proteomic levels revealed the presence of the complete type I secretion system and type II secretion system in this strain. Moreover, this strain also exhibits complete Sec translocase and Tat translocase systems. The extracellular proteome analysis of L. interrogans will supplement the previously generated whole proteome data and provide more information for studying the functions of specific proteins in the infection process and for selecting candidate molecules for vaccines or diagnostic tools for leptospirosis.

Proteome-wide selected reaction monitoring assays for the human pathogen Streptococcus pyogenes

Selected reaction monitoring mass spectrometry (SRM-MS) is a targeted proteomics technology used to identify and quantify proteins with high sensitivity, specificity and high reproducibility. Execution of SRM-MS relies on protein-specific SRM assays, a set of experimental parameters that requires considerable effort to develop. Here we present a proteome-wide SRM assay repository for the gram-positive human pathogen group A Streptococcus. Using a multi-layered approach we generated SRM assays for 10,412 distinct group A Streptococcus peptides followed by extensive testing of the selected reaction monitoring assays in >200 different group A Streptococcus protein pools. Based on the number of SRM assay observations we created a rule-based selected reaction monitoring assay-scoring model to select the most suitable assays per protein for a given cellular compartment and bacterial state. The resource described here represents an important tool for deciphering the group A Streptococcus proteome using selected reaction monitoring and we anticipate that concepts described here can be extended to other pathogens.

Selected reaction monitoring mass spectrometry (SRM-MS) can quantify dynamic changes in protein expression with high sensitivity. Karlsson et al. define optimal detection parameters for 10,412 distinct group A Streptococcus pyogenes peptides, which facilitates proteome-wide SRM-MS studies in this bacterium.

Effects of extracellular DNA and DNA-binding protein on the development of a Streptococcus intermedius biofilm

AIMS

The aim of this study was to clarify the effects of homologous and heterologous extracellular DNAs (eDNAs) and histone-like DNA-binding protein (HLP) on Streptococcus intermedius biofilm development and rigidity.

METHODS AND RESULTS

Formed biofilm mass was measured with 0·1% crystal violet staining method and observed with a scanning electron microscope. The localizations of eDNA and extracellular HLP (eHLP) in formed biofilm were detected by staining with 7-hydoxyl-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) and anti-HLP antibody without fixation, respectively. DNase I treatment (200 U ml(-1)) markedly decreased biofilm formation and cell density in biofilms. Colocalization of eHLP and eDNA in biofilm was confirmed. The addition of eDNA (up to 1 μg ml(-1)) purified from Strep. intermedius, other Gram-positive bacteria, Gram-negative bacteria, or human KB cells into the Strep. intermedius culture increased the biofilm mass of all tested strains of Strep. intermedius, wild-type, HLP-downregulated strain and control strains. In contrast, the addition of eDNA (>1 μg ml(-1)) decreased the biofilm mass of all Strep. intermedius strains.

CONCLUSIONS

These findings demonstrated that eDNA and eHLP play crucial roles in biofilm development and its rigidity.

SIGNIFICANCE AND IMPACT OF THE STUDY

eDNA- and HLP-targeting strategies may be applicable to novel treatments for bacterial biofilm-related infectious diseases.

Streptococcal collagen-like protein A and general stress protein 24 are immunomodulating virulence factors of group A Streptococcus

In Western countries, invasive infections caused by M1T1 serotype group A Streptococcus (GAS) are epidemiologically linked to mutations in the control of virulence regulatory 2-component operon (covRS). In indigenous communities and developing countries, severe GAS disease is associated with genetically diverse non-M1T1 GAS serotypes. Hypervirulent M1T1 covRS mutant strains arise through selection by human polymorphonuclear cells for increased expression of GAS virulence factors such as the DNase Sda1, which promotes neutrophil resistance. The GAS bacteremia isolate NS88.2 (emm 98.1) is a covS mutant that exhibits a hypervirulent phenotype and neutrophil resistance yet lacks the phage-encoded Sda1. Here, we have employed a comprehensive systems biology (genomic, transcriptomic, and proteomic) approach to identify NS88.2 virulence determinants that enhance neutrophil resistance in the non-M1T1 GAS genetic background. Using this approach, we have identified streptococcal collagen-like protein A and general stress protein 24 proteins as NS88.2 determinants that contribute to survival in whole blood and neutrophil resistance in non-M1T1 GAS. This study has revealed new factors that contribute to GAS pathogenicity that may play important roles in resisting innate immune defenses and the development of human invasive infections.

Identification of the immunogenic spore and vegetative proteins of Bacillus anthracis vaccine strain A16R

Immunoproteomics was used to screen the immunogenic spore and vegetative proteins of Bacillus anthracis vaccine strain A16R. The spore and vegetative proteins were separated by 2D gel electrophoresis and transferred to polyvinylidene difluoride membranes, and then western blotting was performed with rabbit immune serum against B.anthracis live spores. Immunogenic spots were cut and digested by trypsin. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry was performed to identify the proteins. As a result, 11 and 45 immunogenic proteins were identified in the spores and vegetative cells, respectively; 26 of which have not been reported previously. To verify their immunogenicity, 12 of the identified proteins were selected to be expressed, and the immune sera from the mice vaccinated by the 12 expressed proteins, except BA0887, had a specific western blot band with the A16R whole cellular lytic proteins. Some of these immunogenic proteins might be used as novel vaccine candidates themselves or for enhancing the protective efficacy of a protective-antigen-based vaccine.

Proteomic biomarkers associated with Streptococcus agalactiae invasive genogroups

Group B streptococcus (GBS, Streptococcus agalactiae) is a leading cause of meningitis and sepsis in newborns and an etiological agent of meningitis, endocarditis, osteoarticular and soft tissue infections in adults. GBS isolates are routinely clustered in serotypes and in genotypes. At present one GBS sequence type (i.e. ST17) is considered to be closely associated with bacterial invasiveness and novel proteomic biomarkers could make a valuable contribution to currently available GBS typing data. For that purpose we analyzed the protein profiles of 170 genotyped GBS isolates by Surface-Enhanced Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SELDI). Univariate statistical analysis of the SELDI profiles identified four protein biomarkers significantly discriminating ST17 isolates from those of the other sequence types. Two of these biomarkers (MW of 7878 Da and 12200 Da) were overexpressed and the other two (MW of 6258 Da and 10463 Da) were underexpressed in ST17. The four proteins were isolated by mass spectrometry-assisted purification and their tryptic peptides analyzed by LC-MS/MS. They were thereby identified as the small subunit of exodeoxyribonuclease VII, the 50S ribosomal protein L7/L12, a CsbD-like protein and thioredoxin, respectively. In conclusion, we identified four candidate biomarkers of ST17 by SELDI for high-throughput screening. These markers may serve as a basis for further studies on the pathophysiology of GBS infection, and for the development of novel vaccines.

Regulation of inhibition of neutrophil infiltration by the two-component regulatory system CovRS in subcutaneous murine infection with group A streptococcus

Hypervirulent invasive group A streptococcus (GAS) isolates inhibit neutrophil infiltration more than pharyngitis isolates do, and the molecular basis of this difference is not well understood. This study was designed to first determine whether natural null mutation of the two-component regulatory system CovRS is responsible for the enhancement of the inhibition of neutrophil recruitment seen in hypervirulent GAS. Next, we examined the role of CovRS-regulated interleukin-8/CXC chemokine peptidase (SpyCEP), C5a peptidase (ScpA), and platelet-activating factor acetylhydrolase (SsE) in the enhanced innate immune evasion. Invasive isolate MGAS5005 induces less neutrophil infiltration and produced a greater lesion area than pharyngitis isolate MGAS2221 in subcutaneous infections of mice. It is known that MGAS5005, but not MGAS2221, has a natural 1-bp deletion in the covS gene. Replacement of covS(Δ1bp) in MGAS5005 with wild-type covS resulted in the MGAS2221 phenotype. Deletion of covS from MGAS2221 resulted in the MGAS5005 phenotype. Tests of single, double, and triple deletion mutants of the MGAS5005 sse, spyCEP, and scpA genes found that SsE plays a more important role than SpyCEP and ScpA in the inhibition of neutrophil recruitment and that SsE, SpyCEP, and ScpA do not have synergistic effects on innate immune evasion by MGAS5005. Deletion of sse, but not spyCEP or scpA, of MGAS2221 enhances neutrophil recruitment. Thus, covS null mutations can cause substantial inhibition of neutrophil recruitment by enhancing the expression of the chemoattractant-degrading virulence factors, and SsE, but not SpyCEP or ScpA, is required for CovRS-regulated GAS inhibition of neutrophil infiltration.

Human pathogenic streptococcal proteomics and vaccine development

Gram-positive streptococci are non-motile, chain-forming bacteria commonly found in the normal oral and bowel flora of warm-blooded animals. Over the past decade, a proteomic approach combining 2-DE and MS has been used to systematically map the cellular, surface-associated and secreted proteins of human pathogenic streptococcal species. The public availability of complete streptococcal genomic sequences and the amalgamation of proteomic, genomic and bioinformatic technologies have recently facilitated the identification of novel streptococcal vaccine candidate antigens and therapeutic agents. The objective of this review is to examine the constituents of the streptococcal cell wall and secreted proteome, the mechanisms of transport of surface and secreted proteins, and describe the current methodologies employed for the identification of novel surface-displayed proteins and potential vaccine antigens.

Conserved anchorless surface proteins as group A streptococcal vaccine candidates

Streptococcus pyogenes (group A Streptococcus (GAS)) causes ∼700 million human infections each year, resulting in over 500,000 deaths. The development of a commercial GAS vaccine is hampered by the occurrence of many unique GAS serotypes, antigenic variation within the same serotype, differences in serotype geographical distribution, and the production of antibodies cross-reactive with human tissue that may lead to autoimmune disease. Several independent studies have documented a number of GAS cell wall-associated or secreted metabolic enzymes that contain neither N-terminal leader sequences nor C-terminal cell wall anchors. Here, we applied a proteomic analysis of serotype M1T1 GAS cell wall extracts for the purpose of vaccine development. This approach catalogued several anchorless proteins and identified two protective vaccine candidates, arginine deiminase and trigger factor. These surface-exposed enzymes are expressed across multiple GAS serotypes exhibiting ≥99% amino acid sequence identity. Vaccine safety concerns are alleviated by the observation that these vaccine candidates lack human homologs, while sera from human populations suffering repeated GAS infections and high levels of autoimmune complications do not recognize these enzymes. Our study demonstrates anchorless cell surface antigens as promising vaccine candidates for the prevention of GAS disease.

Growth phase-dependent modulation of Rgg binding specificity in Streptococcus pyogenes

Streptococcus pyogenes Rgg is a transcriptional regulator that interacts with the cofactor LacD.1 to control growth phase-dependent expression of genes, including speB, which encodes a secreted cysteine protease. LacD.1 is thought to interact with Rgg when glycolytic intermediates are abundant in a manner that prevents Rgg-mediated activation of speB expression via binding to the promoter region. When the intermediates diminish, LacD.1 dissociates from Rgg and binds to the speB promoter to activate expression. The purpose of this study was to determine if Rgg bound to chromatin during the exponential phase of growth and, if so, to identify the binding sites. Rgg bound to 62 chromosomal sites, as determined by chromatin immunoprecipitation coupled with DNA microarrays. Thirty-eight were within noncoding DNA, including sites upstream of the genes encoding the M protein (M49), serum opacity factor (SOF), fibronectin-binding protein (SfbX49), and a prophage-encoded superantigen, SpeH. Each of these sites contained a promoter that was regulated by Rgg, as determined with transcriptional fusion assays. Purified Rgg also bound to the promoter regions of emm49, sof, and sfbX49 in vitro. Results obtained with a lacD.1 mutant showed that both LacD.1 and Rgg were necessary for the repression of emm49, sof, sfbX49, and speH expression. Overall, the results indicated that the DNA binding specificity of Rgg is responsive to environmental changes in a LacD.1-dependent manner and that Rgg and LacD.1 directly control virulence gene expression in the exponential phase of growth.

Streptococcal IdeS and its impact on immune response and inflammation

Survival of the important bacterial pathogen Streptococcus pyogenes relies on its ability to circumvent the antimicrobial actions of innate and specific immune responses and to modulate the inflammatory responses induced during the course of an infection. Inflammatory processes play key roles during streptococcal pathogenesis and streptococcal infections are accompanied by an intense inflammatory state. As an exclusively human pathogen, S. pyogenes has adapted to the various countermeasures employed by its host to fight bacterial infections, in particular to interfere with the effector functions of immunoglobulin G (IgG). For this purpose, S. pyogenes has evolved an IgG-specific endopeptidase, IdeS, which is highly specific for the lower hinge region of IgG. This review summarizes the current knowledge about this intriguing enzyme as well as its role in inflammation and in the attenuation of human immune responses towards streptococcal infection.

Srv mediated dispersal of streptococcal biofilms through SpeB is observed in CovRS+ strains

Group A Streptococcus (GAS) is a human specific pathogen capable of causing both mild infections and severe invasive disease. We and others have shown that GAS is able to form biofilms during infection. That is to say, they form a three-dimensional, surface attached structure consisting of bacteria and a multi-component extracellular matrix. The mechanisms involved in regulation and dispersal of these GAS structures are still unclear. Recently we have reported that in the absence of the transcriptional regulator Srv in the MGAS5005 background, the cysteine protease SpeB is constitutively produced, leading to increased tissue damage and decreased biofilm formation during a subcutaneous infection in a mouse model. This was interesting because MGAS5005 has a naturally occurring mutation that inactivates the sensor kinase domain of the two component regulatory system CovRS. Others have previously shown that strains lacking covS are associated with decreased SpeB production due to CovR repression of speB expression. Thus, our results suggest the inactivation of srv can bypass CovR repression and lead to constitutive SpeB production. We hypothesized that Srv control of SpeB production may be a mechanism to regulate biofilm dispersal and provide a mechanism by which mild infection can transition to severe disease through biofilm dispersal. The question remained however, is this mechanism conserved among GAS strains or restricted to the unique genetic makeup of MGAS5005. Here we show that Srv mediated control of SpeB and biofilm dispersal is conserved in the invasive clinical isolates RGAS053 (serotype M1) and MGAS315 (serotype M3), both of which have covS intact. This work provides additional evidence that Srv regulated control of SpeB may mediate biofilm formation and dispersal in diverse strain backgrounds.

The deficient cleavage of M protein-bound IgG by IdeS: insight into the escape of Streptococcus pyogenes from antibody-mediated immunity

IdeS (IgG-degrading enzyme of Streptococcus pyogenes) is a virulence factor for S. pyogenes, group A Streptococcus (GAS). IdeS is believed to allow GAS to evade antibody-mediated phagocytosis by cleaving IgG at the lower hinge region. Human immunoglobulins bind to the GAS surface by two mechanisms: Specific antibodies attach at the Fab region to their specific antigens on the bacterial surface. Immunoglobulins can also attach nonspecifically at the Fc region to streptococcal M and M-like proteins. This phenomenon is believed to form the host-like coat and to block the recognition of Fc region by Fc receptor on phagocytes and antibody-dependent cell-mediated cytotoxicity. It is not known whether IdeS preferentially cleaves IgG attached at the Fab or Fc regions. To explore this issue, we used Sepharose beads coated with protein A or L or M protein as surrogate markers for specific (Fab) and nonspecific (Fc) binding sites. We found that IdeS cleaved Fab-bound IgG as rapidly as soluble IgG. In contrast, Fc-bound IgG was cleaved about 4 fold less than soluble IgG. In a competitive binding assay, we found that M protein had a greater affinity than IdeS to attach to the Fc region of human IgG. Thus, IdeS exhibited preferential IgG endopeptidase activity for Fab-bound IgG while allowing the non-specific binding of IgG to remain attached to M protein. We propose that this preferential enzymatic activity accounts for the ability of GAS to resist immunoglobulin-mediated phagocytosis and cytotoxicity.

Evolution of diversity in epidemics revealed by analysis of the human bacterial pathogen group A Streptococcus

Advancements in high-throughput, high-volume data generating techniques increasingly present us with opportunities to probe new areas of biology. In this work we assessed the extent to which four closely related and genetically representative strains of group A Streptococcus causing epidemic disease have differentiated from one another. Comparative genome sequencing, expression microarray analysis, and proteomic studies were used in parallel to assess strain variation. The extent of phenotypic differentiation was unexpectedly large. We found significant associations between genetic polymorphisms and alterations in gene expression allowing us to estimate the frequency with which specific types of polymorphisms alter gene transcription. We identified polymorphisms in the gene (ropB) encoding the RopB regulator that associate with altered transcription of speB and production of the SpeB protein, a critical secreted protease virulence factor. Although these four epidemic strains are closely related, a key discovery is that accumulation of modest genetic changes has rapidly resulted in significant strain phenotypic differentiation, including the extracellular proteome that contains multiple virulence factors. These data provide enhanced understanding of genetic events resulting in strain variation in bacterial epidemics.

Serine/threonine protein kinase Stk is required for virulence, stress response, and penicillin tolerance in Streptococcus pyogenes

Genes encoding one or more Ser/Thr protein kinases have been identified recently in many bacteria, including one (stk) in the human pathogen Streptococcus pyogenes (group A streptococcus [GAS]). We report that in GAS, stk is required to produce disease in a murine myositis model of infection. Using microarray and quantitative reverse transcription-PCR (qRT-PCR) studies, we found that Stk activates genes for virulence factors, osmoregulation, metabolism of α-glucans, and fatty acid biosynthesis, as well as genes affecting cell wall synthesis. Confirming these transcription studies, we determined that the stk deletion mutant is more sensitive to osmotic stress and to penicillin than the wild type. We discuss several possible Stk phosphorylation targets that might explain Stk regulation of expression of specific operons and the possible role of Stk in resuscitation from quiescence.

Application of both high-performance liquid chromatography combined with tandem mass spectrometry shotgun and 2-D polyacrylamide gel electrophoresis for streptococcal exoproteins gave reliable proteomic data

Streptococci secrete a large number of exoproteins including virulence-associated toxins and enzymes. To construct a reliable database of streptococcal exoproteins, we integrated the results that were derived from two approaches: LC-based shotgun proteomic analysis and 2-D PAGE-based proteomic analysis. We identified 74 and 82 proteins by LC-based and gel-based analysis, respectively. Forty-five proteins were identified by both methods. In addition, two proteins, one identified by both methods and the other only by LC-based shotgun analysis, were newly annotated. We therefore found the importance of combinational analysis by the two methods for the construction of a more reliable database.

Complete genome sequence and immunoproteomic analyses of the bacterial fish pathogen Streptococcus parauberis

Although Streptococcus parauberis is known as a bacterial pathogen associated with bovine udder mastitis, it has recently become one of the major causative agents of olive flounder (Paralichthys olivaceus) streptococcosis in northeast Asia, causing massive mortality resulting in severe economic losses. S. parauberis contains two serotypes, and it is likely that capsular polysaccharide antigens serve to differentiate the serotypes. In the present study, the complete genome sequence of S. parauberis (serotype I) was determined using the GS-FLX system to investigate its phylogeny, virulence factors, and antigenic proteins. S. parauberis possesses a single chromosome of 2,143,887 bp containing 1,868 predicted coding sequences (CDSs), with an average GC content of 35.6%. Whole-genome dot plot analysis and phylogenetic analysis of a 60-kDa chaperonin-encoding gene and the glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-encoding gene showed that the strain was evolutionarily closely related to Streptococcus uberis. S. parauberis antigenic proteins were analyzed using an immunoproteomic technique. Twenty-one antigenic protein spots were identified in S. parauberis, by reaction with an antiserum obtained from S. parauberis-challenged olive flounder. This work provides the foundation needed to understand more clearly the relationship between pathogen and host and develops new approaches toward prophylactic and therapeutic strategies to deal with streptococcosis in fish. The work also provides a better understanding of the physiology and evolution of a significant representative of the Streptococcaceae.

Naturally occurring single amino acid replacements in a regulatory protein alter streptococcal gene expression and virulence in mice

Infection with different strains of the same species of bacteria often results in vastly different clinical outcomes. Despite extensive investigation, the genetic basis of microbial strain-specific virulence remains poorly understood. Recent whole-genome sequencing has revealed that SNPs are the most prevalent form of genetic diversity among different strains of the same species of bacteria. For invasive serotype M3 group A streptococci (GAS) strains, the gene encoding regulator of proteinase B (RopB) has the highest frequency of SNPs. Here, we have determined that ropB polymorphisms alter RopB function and modulate GAS host-pathogen interactions. Sequencing of ropB in 171 invasive serotype M3 GAS strains identified 19 distinct ropB alleles. Inactivation of the ropB gene in strains producing distinct RopB variants had dramatically divergent effects on GAS global gene expression. Additionally, generation of isoallelic GAS strains differing only by a single amino acid in RopB confirmed that variant proteins affected transcript levels of the gene encoding streptococcal proteinase B, a major RopB-regulated virulence factor. Comparison of parental, RopB-inactivated, and RopB isoallelic strains in mouse infection models demonstrated that ropB polymorphisms influence GAS virulence and disease manifestations. These data detail a paradigm in which unbiased, whole-genome sequence analysis of populations of clinical bacterial isolates creates new avenues of productive investigation into the pathogenesis of common human infections.

The Streptococcus pyogenes proteome: maps, virulence factors and vaccine candidates

Streptococcus pyogenes is an important cause of human morbidity and mortality worldwide. A wealth of genomic information related to this pathogen has facilitated exploration of the proteome, particularly in response to environmental conditions thought to mimic various aspects of pathogenesis. Proteomic approaches are also used to identify immunoreactive proteins for vaccine development and to identify proteins that may induce autoimmunity. These studies have revealed new mechanisms involved in regulating the S. pyogenes proteome, which has opened up new avenues in the study of S. pyogenes pathogenesis. This article describes the methods used, and progress being made towards characterizing the S. pyogenes proteome, including studies seeking to identify potential vaccine candidates.

Benfang Lei’s research on heme acquisition in Gram-positive pathogens and bacterial pathogenesis

Benfang Lei’s laboratory conducts research on pathogenesis of human pathogen Group A Streptococcus (GAS) and horse pathogen Streptococcus equi (S. equi). His current research focuses on heme acquisition in Gram-positive pathogens and molecular mechanism of GAS and S. equi pathogenesis. Heme is an important source of essential iron for bacterial pathogens. Benfang Lei and colleagues identified the first cell surface heme-binding protein in Gram-positive pathogens and the heme acquisition system in GAS, demonstrated direct heme transfer from one protein to another, demonstrated an experimental pathway of heme acquisition by the Staphylococcus aureus Isd system, elucidated the activated heme transfer mechanism, and obtained evidence for a chemical mechanism of direct axial ligand displacement during the Shp-to-HtsA heme transfer reaction. These findings have considerably contributed to the progress that has been made over recent years in understanding the heme acquisition process in Gram-positive pathogens. Pathogenesis of GAS is mediated by an abundance of extracellular proteins, and pathogenic role and functional mechanism are not known for many of these virulence factors. Lei laboratory identified a secreted protein of GAS as a CovRS-regulated virulence factor that is a protective antigen and is critical for GAS spreading in the skin and systemic dissemination. These studies may lead to development of novel strategies to prevent and treat GAS infections.

A streptococcal effector protein that inhibits Porphyromonas gingivalis biofilm development

Dental plaque formation is a developmental process involving cooperation and competition within a diverse microbial community, approximately 70 % of which is composed of an array of streptococci during the early stages of supragingival plaque formation. In this study, 79 cell-free culture supernatants from a variety of oral streptococci were screened to identify extracellular compounds that inhibit biofilm formation by the oral anaerobe Porphyromonas gingivalis strain 381. The majority of the streptococcal supernatants (61 isolates) resulted in lysis of P. gingivalis cells, and some (17 isolates) had no effect on cell viability, growth or biofilm formation. One strain, however, produced a supernatant that abolished biofilm formation without affecting growth rate. Analysis of this activity led to the discovery that a 48 kDa protein was responsible for the inhibition. Protein sequence identification and enzyme activity assays identified the effector protein as an arginine deiminase. To identify the mechanism(s) by which this protein inhibits biofilm formation, we began by examining the expression levels of genes encoding fimbrial subunits; surface structures known to be involved in biofilm development. Quantitative RT-PCR analysis revealed that exposure of P. gingivalis cells to this protein for 1 h resulted in the downregulation of genes encoding proteins that are the major subunits of two distinct types of thin, single-stranded fimbriae (fimA and mfa1). Furthermore, this downregulation occurred in the absence of arginine deiminase enzymic activity. Hence, our data indicate that P. gingivalis can sense this extracellular protein, produced by an oral streptococcus (Streptococcus intermedius), and respond by downregulating expression of cell-surface appendages required for attachment and biofilm development.

Novel conserved group A streptococcal proteins identified by the antigenome technology as vaccine candidates for a non-M protein-based vaccine

Group A streptococci (GAS) can cause a wide variety of human infections ranging from asymptomatic colonization to life-threatening invasive diseases. Although antibiotic treatment is very effective, when left untreated, Streptococcus pyogenes infections can lead to poststreptococcal sequelae and severe disease causing significant morbidity and mortality worldwide. To aid the development of a non-M protein-based prophylactic vaccine for the prevention of group A streptococcal infections, we identified novel immunogenic proteins using genomic surface display libraries and human serum antibodies from donors exposed to or infected by S. pyogenes. Vaccine candidate antigens were further selected based on animal protection in murine lethal-sepsis models with intranasal or intravenous challenge with two different M serotype strains. The nine protective antigens identified are highly conserved; eight of them show more than 97% sequence identity in 13 published genomes as well as in approximately 50 clinical isolates tested. Since the functions of the selected vaccine candidates are largely unknown, we generated deletion mutants for three of the protective antigens and observed that deletion of the gene encoding Spy1536 drastically reduced binding of GAS cells to host extracellular matrix proteins, due to reduced surface expression of GAS proteins such as Spy0269 and M protein. The protective, highly conserved antigens identified in this study are promising candidates for the development of an M-type-independent, protein-based vaccine to prevent infection by S. pyogenes.

IgG Endopeptidase SeMac does not Inhibit Opsonophagocytosis of Streptococcus equi Subspecies equi by Horse Polymorphonuclear Leukocytes

The secreted Mac protein made by group A Streptococcus (GAS) inhibits opsonophagocytosis of GAS by human polymorphonuclear leukocytes (PMNs). This protein also has the endopeptidase activity against human immunoglobulin G (IgG), and the Cys94, His262 and Asp284 are critical for the enzymatic activity. The horse pathogen Streptococcus equi subspecies equi produces a homologue of Mac (SeMac). SeMac was characterized to determine whether SeMac has IgG endopeptidase activity and inhibits opsonophagocytosis of S. equi by horse PMNs. The gene was cloned and recombinant SeMac was overexpressed in Escherichia coli and purified to homogeneity. Mice with experimental S. equi infection and horses with strangles caused by S. equi seroconverted to SeMac, indicating that SeMac is produced in vivo during infection. SeMac has endopeptidase activity against human IgG. However, the protein just cleaves a small fraction, which may be IgG1 only, of horse IgG. Replacement of Cys102 with Ser or His272 with Ala abolishes the enzymatic activity of SeMac, and the Asp294Ala mutation greatly decreases the enzymatic activity. SeMac does not inhibit opsonophagocytosis of S. equi by horse PMNs but opsonophagocytosis of GAS by human PMNs. Thus, SeMac is a cysteine endopeptidase with a limited activity against horse IgG and must have other function.

Adaptation of group A Streptococcus to human amniotic fluid

BACKGROUND

For more than 100 years, group A Streptococcus has been identified as a cause of severe and, in many cases, fatal infections of the female urogenital tract. Due to advances in hospital hygiene and the advent of antibiotics, this type of infection has been virtually eradicated. However, within the last three decades there has been an increase in severe intra- and post-partum infections attributed to GAS.

METHODOLOGY

We hypothesized that GAS alters its transcriptome to survive in human amniotic fluid (AF) and cause disease. To identify genes that were up or down regulated in response to growth in AF, GAS was grown in human AF or standard laboratory media (THY) and samples for expression microarray analysis were collected during mid-logarithmic, late-logarithmic, and stationary growth phases. Microarray analysis was performed using a custom Affymetrix chip and normalized hybridization values derived from three biological replicates were collected at each growth point. Ratios of AF/THY above a 2-fold change and P-value <0.05 were considered significant.

PRINCIPAL FINDINGS

The majority of changes in the GAS transcriptome involved down regulation of multiple adhesins and virulence factors and activation of the stress response. We observed significant changes in genes involved in the arginine deiminase pathway and in the nucleotide de novo synthesis pathway.

CONCLUSIONS/SIGNIFICANCE

Our work provides new insight into how pathogenic bacteria respond to their environment to establish infection and cause disease.

Characterization of Streptococcus pyogenes beta-NAD+ glycohydrolase: re-evaluation of enzymatic properties associated with pathogenesis

The gram-positive pathogen Streptococcus pyogenes injects a beta-NAD(+) glycohydrolase (SPN) into the cytosol of an infected host cell using the cytolysin-mediated translocation pathway. In this compartment, SPN accelerates the death of the host cell by an unknown mechanism that may involve its beta-NAD(+)-dependent enzyme activities. SPN has been reported to possess the unique characteristic of not only catalyzing hydrolysis of beta-NAD(+), but also carrying out ADP-ribosyl cyclase and ADP-ribosyltransferase activities, making SPN the only beta-NAD(+) glycohydrolase that can catalyze all of these reactions. With the long term goal of understanding how these activities may contribute to pathogenesis, we have further characterized the enzymatic activity of SPN using highly purified recombinant protein. Kinetic studies of the multiple activities of SPN revealed that SPN possessed only beta-NAD(+) hydrolytic activity and lacked detectable ADP-ribosyl cyclase and ADP-ribosyltransferase activities. Similarly, SPN was unable to catalyze cyclic ADPR hydrolysis, and could not catalyze methanolysis or transglycosidation. Kinetic analysis of product inhibition by recombinant SPN demonstrated an ordered uni-bi mechanism, with ADP-ribose being released as a second product. SPN was unaffected by product inhibition using nicotinamide, suggesting that this moiety contributes little to the binding energy of the substrate. Upon transformation, SPN was toxic to Saccharomyces cerevisiae, whereas a glycohydrolase-inactive SPN allowed for viability. Taken together, these data suggest that SPN functions exclusively as a strict beta-NAD(+) glycohydrolase during pathogenesis.

A case of structure determination using pseudosymmetry

Here, a case is presented of an unusual structure determination which was facilitated by the use of pseudosymmetry. Group A streptococcus uses cysteine protease Mac-1 (also known as IdeS) to evade the host immune system. Native Mac-1 was crystallized in the orthorhombic space group P2(1)2(1)2. Surprisingly, crystals of the inactive C94A mutant of Mac-1 displayed monoclinic symmetry with space group P2(1), despite the use of native orthorhombic Mac-1 microcrystals for seeding. Attempts to solve the structure of the C94A mutant by MAD phasing in the monoclinic space group did not produce an interpretable map. The native Patterson map of the C94A mutant showed two strong peaks along the (1 0 1) diagonal, indicating possible translational pseudosymmetry in space group P2(1). Interestingly, one-third of the monoclinic reflections obeyed pseudo-orthorhombic P2(1)2(1)2 symmetry similar to that of the wild-type crystals and could be indexed and processed in this space group. The pseudo-orthorhombic and monoclinic unit cells were related by the following vector operations: a(m) = b(o) - c(o), b(m) = a(o) and c(m) = -2c(o) - b(o). The pseudo-orthorhombic subset of data produced good SAD phases, leading to structure determination with one monomer in the asymmetric unit. Subsequently, the structure of the Mac-1 mutant in the monoclinic form was determined by molecular replacement, which showed six molecules forming three translationally related dimers aligned along the (1 0 1) diagonal. Knowing the geometric relationship between the pseudo-orthorhombic and the monoclinic unit cells, all six molecules can be generated in the monoclinic unit cell directly without the use of molecular replacement. The current case provides a successful example of the use of pseudosymmetry as a powerful phase-averaging method for structure determination by anomalous diffraction techniques. In particular, a structure can be solved in a higher pseudosymmetry subcell in which an NCS operator becomes a crystallographic operator. The geometrical relationships between the subcell and parental cell can be used to generate a complete molecular representation of the parental asymmetric unit for refinement.

A decade of molecular pathogenomic analysis of group A Streptococcus

Molecular pathogenomic analysis of the human bacterial pathogen group A Streptococcus has been conducted for a decade. Much has been learned as a consequence of the confluence of low-cost DNA sequencing, microarray technology, high-throughput proteomics, and enhanced bioinformatics. These technical advances, coupled with the availability of unique bacterial strain collections, have facilitated a systems biology investigative strategy designed to enhance and accelerate our understanding of disease processes. Here, we provide examples of the progress made by exploiting an integrated genome-wide research platform to gain new insight into molecular pathogenesis. The studies have provided many new avenues for basic and translational research.