Comprehensive study of antimicrobial susceptibility pattern and extended spectrum beta-lactamase (ESBL) prevalence in bacteria isolated from urine samples

Nowadays, increasing extended-spectrum β-lactamase (ESBL)-producing bacteria have become a global concern because of inducing resistance toward most of the antimicrobial classes and making the treatment difficult. In order to achieve an appropriate treatment option, identification of the prevalent species which generate ESBL as well as their antibiotic susceptibility pattern is essential worldwide. Hence, this study aimed to investigate the prevalence of ESBL-producing bacteria and assess their drug susceptibility in Fardis Town, Iran. A total of 21,604 urine samples collected from patients suspected to have urinary tract infection (UTI) were processed in the current study. The antimicrobial susceptibility of the isolates was tested by the disk diffusion method. The ESBL producing bacteria were determined by Double Disc Synergy Test (DDST) procedure. Bacterial growth was detected in 1408 (6.52%) cases. The most common bacterial strains causing UTI were found E. coli (72.16%), followed by K. pneumoniae (10.3%) and S. agalactiae (5.7%). Overall, 398 (28.26%) were ESBL producer. The highest ESBL production was observed in E. coli, followed by Klebsiella species. ESBL producers revealed a higher level of antibiotic resistance compared with non-ESBLs. In conclusion, ESBL production in uropathogens was relatively high. Carbapenems and Aminoglycosides were confirmed as the most effective treatment options for these bacteria.

Enhanced production of streptokinase from Streptococcus agalactiae EBL-31 by response surface methodology

Streptokinase (SK) is a fibrinolytic protein used for the treatment of cardiovascular disorders. In the present study, enhanced production of SK was achieved by determining the optimum fermentation conditions for the maximum growth of Streptococcus agalactiae EBL-31 using response surface methodology (RSM). Four process variables (pH, temperature, incubation time and inoculum size) with five levels were evaluated in 30 experimental runs. Central composite rotatable design (CCRD) was employed to predict the effect of independent variables on SK activity. The statistical evaluation by ANOVA showed that the model was fit as the effect of single factors, quadratic effects and most of the interactions among variables. The value ofR2 (0.9988) indicated the satisfactory interaction between the experimental and predicted responses. Furthermore, the model F value (902.67) and coefficient of variation (1.92) clearly showed that the model is significant (p =>0.0001). The functional activity of SK was determined by spectrophotometric analysis and maximum SK production was obtained at pH-7.0, temperature- 37.5oC, an incubation time of 36 hours and 2.5 mL inoculum size. Hence it was concluded that the optimization of culture conditions through RSM increases the production of SK by 2.01-fold. Production of SK by fermentation is an economical choice to be used for the treatment of cardiovascular diseases.

High-resolution crystal structure of Streptococcus agalactiae glyceraldehyde-3-phosphate dehydrogenase

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme that plays critical roles in bacterial pathogenesis in some pathogenic bacteria. In this study, the crystal structure of group B streptococcus GAPDH was determined at 1.36 Å resolution. The structure contained an asymmetric mixed holo tetramer, with two NAD ligands bound to two protomers. Further structural analysis identified interesting phosphate ion-binding sites, which shed light on its catalytic mechanism.

Quantitative assessment of the blood-brain barrier opening caused by Streptococcus agalactiae hyaluronidase in a BALB/c mouse model

Streptococcus agalactiae is a pathogen causing meningitis in animals and humans. However, little is known about the entry of S. agalactiae into brain tissue. In this study, we developed a BALB/c mouse model based on the intravenous injection of β-galactosidase-positive Escherichia coli M5 as an indicator of blood-brain barrier (BBB) opening. Under physiological conditions, the BBB is impermeable to E. coli M5. In pathological conditions caused by S. agalactiae, E. coli M5 is capable of penetrating the brain through a disrupted BBB. The level of BBB opening can be assessed by quantitative measurement of E. coli M5 loads per gram of brain tissue. Further, we used the model to evaluate the role of S. agalactiae hyaluronidase in BBB opening. The inactivation of hylB gene encoding a hyaluronidase, HylB, resulted in significantly decreased E. coli M5 colonization, and the intravenous injection of purified HylB protein induced BBB opening in a dose-dependent manner. This finding verified the direct role of HylB in BBB invasion and traversal, and further demonstrated the practicability of the in vivo mouse model established in this study. This model will help to understand the S. agalactiae-host interactions that are involved in this bacterial traversal of the BBB and to develop efficacious strategies to prevent central nervous system infections.

Crystal Structures of Group B Streptococcus Glyceraldehyde-3-Phosphate Dehydrogenase: Apo-Form, Binary and Ternary Complexes

Glyceraldehyde 3-phosphate dehydrogenase or GAPDH is an evolutionarily conserved glycolytic enzyme. It catalyzes the two step oxidative phosphorylation of D-glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate using inorganic phosphate and NAD+ as cofactor. GAPDH of Group B Streptococcus is a major virulence factor and a potential vaccine candidate. Moreover, since GAPDH activity is essential for bacterial growth it may serve as a possible drug target. Crystal structures of Group B Streptococcus GAPDH in the apo-form, two different binary complexes and the ternary complex are described here. The two binary complexes contained NAD+ bound to 2 (mixed-holo) or 4 (holo) subunits of the tetrameric protein. The structure of the mixed-holo complex reveals the effects of NAD+ binding on the conformation of the protein. In the ternary complex, the phosphate group of the substrate was bound to the new Pi site in all four subunits. Comparison with the structure of human GAPDH showed several differences near the adenosyl binding pocket in Group B Streptococcus GAPDH. The structures also reveal at least three surface-exposed areas that differ in amino acid sequence compared to the corresponding areas of human GAPDH.

Structure and Inhibition of Microbiome β-Glucuronidases Essential to the Alleviation of Cancer Drug Toxicity

The selective inhibition of bacterial β-glucuronidases was recently shown to alleviate drug-induced gastrointestinal toxicity in mice, including the damage caused by the widely used anticancer drug irinotecan. Here, we report crystal structures of representative β-glucuronidases from the Firmicutes Streptococcus agalactiae and Clostridium perfringens and the Proteobacterium Escherichia coli, and the characterization of a β-glucuronidase from the Bacteroidetes Bacteroides fragilis. While largely similar in structure, these enzymes exhibit marked differences in catalytic properties and propensities for inhibition, indicating that the microbiome maintains functional diversity in orthologous enzymes. Small changes in the structure of designed inhibitors can induce significant conformational changes in the β-glucuronidase active site. Finally, we establish that β-glucuronidase inhibition does not alter the serum pharmacokinetics of irinotecan or its metabolites in mice. Together, the data presented advance our in vitro and in vivo understanding of the microbial β-glucuronidases, a promising new set of targets for controlling drug-induced gastrointestinal toxicity.

Overexpression, purification, crystallization and preliminary X-ray diffraction of the nisin resistance protein from Streptococcus agalactiae

Nisin is a 34-amino-acid antimicrobial peptide produced by Lactococcus lactis belonging to the class of lantibiotics. Nisin displays a high bactericidal activity against various Gram-positive bacteria, including some human-pathogenic strains. However, there are some nisin-non-producing strains that are naturally resistant owing to the presence of the nsr gene within their genome. The encoded protein, NSR, cleaves off the last six amino acids of nisin, thereby reducing its bactericidal efficacy. An expression and purification protocol has been established for the NSR protein from Streptococcus agalactiae COH1. The protein was successfully crystallized using the vapour-diffusion method in hanging and sitting drops, resulting in crystals that diffracted X-rays to 2.8 and 2.2 Å, respectively.

Structural characterization of the virulence factor nuclease A from Streptococcus agalactiae

The group B pathogen Streptococcus agalactiae commonly populates the human gut and urogenital tract, and is a major cause of infection-based mortality in neonatal infants and in elderly or immunocompromised adults. Nuclease A (GBS_NucA), a secreted DNA/RNA nuclease, serves as a virulence factor for S. agalactiae, facilitating bacterial evasion of the human innate immune response. GBS_NucA efficiently degrades the DNA matrix component of neutrophil extracellular traps (NETs), which attempt to kill and clear invading bacteria during the early stages of infection. In order to better understand the mechanisms of DNA substrate binding and catalysis of GBS_NucA, the high-resolution structure of a catalytically inactive mutant (H148G) was solved by X-ray crystallography. Several mutants on the surface of GBS_NucA which might influence DNA substrate binding and catalysis were generated and evaluated using an imidazole chemical rescue technique. While several of these mutants severely inhibited nuclease activity, two mutants (K146R and Q183A) exhibited significantly increased activity. These structural and biochemical studies have greatly increased our understanding of the mechanism of action of GBS_NucA in bacterial virulence and may serve as a foundation for the structure-based drug design of antibacterial compounds targeted to S. agalactiae.

Structure of Streptococcus agalactiae glyceraldehyde-3-phosphate dehydrogenase holoenzyme reveals a novel surface

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a conserved cytosolic enzyme, which plays a key role in glycolysis. GAPDH catalyzes the oxidative phosphorylation of D-glyceraldehyde 3-phosphate using NAD or NADP as a cofactor. In addition, GAPDH localized on the surface of some bacteria is thought to be involved in macromolecular interactions and bacterial pathogenesis. GAPDH on the surface of group B streptococcus (GBS) enhances bacterial virulence and is a potential vaccine candidate. Here, the crystal structure of GBS GAPDH from Streptococcus agalactiae in complex with NAD is reported at 2.46 Å resolution. Although the overall structure of GBS GAPDH is very similar to those of other GAPDHs, the crystal structure reveals a significant difference in the area spanning residues 294-307, which appears to be more acidic. The amino-acid sequence of this region of GBS GAPDH is also distinct compared with other GAPDHs. This region therefore may be of interest as an immunogen for vaccine development.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of glyceraldehyde-3-phosphate dehydrogenase from Streptococcus agalactiae NEM316

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an essential enzyme involved in glycolysis. Despite lacking the secretory signal sequence, this cytosolic enzyme has been found localized at the surface of several bacteria and fungi. As a surface protein, GAPDH exhibits various adhesive functions, thereby facilitating colonization and invasion of host tissues. Streptococcus agalactiae, also known as group B streptococcus (GBS), binds onto the host using its surface adhesins and causes sepsis and pneumonia in neonates. GAPDH is one of the surface adhesins of GBS binding to human plasminogen and is a virulent factor associated with host colonization. Although the surface-associated GAPDH has been shown to bind to a variety of host extracellular matrix (ECM) molecules in various bacteria, the molecular mechanism underlying their interaction is not fully understood. To investigate this, structural studies on GAPDH of S. agalactiae were initiated. The gapC gene of S. agalactiae NEM316 encoding GAPDH protein was cloned into pET-28a vector, overexpressed in Escherichia coli BL21(DE3) cells and purified to homogeneity. The purified protein was crystallized using the hanging-drop vapour-diffusion method. The GAPDH crystals obtained in two different crystallization conditions diffracted to 2.8 and 2.6 Å resolution, belonging to two different space groups P2₁ and P2₁2₁2₁, respectively. The structure was solved by molecular replacement and structure refinement is now in progress.

Sortase A substrate specificity in GBS pilus 2a cell wall anchoring

Streptococcus agalactiae, also referred to as Group B Streptococcus (GBS), is one of the most common causes of life-threatening bacterial infections in infants. In recent years cell surface pili have been identified in several Gram-positive bacteria, including GBS, as important virulence factors and promising vaccine candidates. In GBS, three structurally distinct types of pili have been discovered (pilus 1, 2a and 2b), whose structural subunits are assembled in high-molecular weight polymers by specific class C sortases. In addition, the highly conserved housekeeping sortase A (SrtA), whose main role is to link surface proteins to bacterial cell wall peptidoglycan by a transpeptidation reaction, is also involved in pili cell wall anchoring in many bacteria. Through in vivo mutagenesis, we demonstrate that the LPXTG sorting signal of the minor ancillary protein (AP2) is essential for pilus 2a anchoring. We successfully produced a highly purified recombinant SrtA (SrtA(ΔN40)) able to specifically hydrolyze the sorting signal of pilus 2a minor ancillary protein (AP2-2a) and catalyze in vitro the transpeptidation reaction between peptidoglycan analogues and the LPXTG motif, using both synthetic fluorescent peptides and recombinant proteins. By contrast, SrtA(ΔN40) does not catalyze the transpeptidation reaction with substrate-peptides mimicking sorting signals of the other pilus 2a subunits (the backbone protein and the major ancillary protein). Thus, our results add further insight into the proposed model of GBS pilus 2a assembly, in which SrtA is required for pili cell wall covalent attachment, acting exclusively on the minor accessory pilin, representing the terminal subunit located at the base of the pilus.

Structural differences between the Streptococcus agalactiae housekeeping and pilus-specific sortases: SrtA and SrtC1

The assembly of pili on the cell wall of Gram-positive bacteria requires transpeptidase enzymes called sortases. In Streptococcus agalactiae, the PI-1 pilus island of strain 2603V/R encodes two pilus-specific sortases (SrtC1 and SrtC2) and three pilins (GBS80, GBS52 and GBS104). Although either pilus-specific sortase is sufficient for the polymerization of the major pilin, GBS80, incorporation of the minor pilins GBS52 and GBS104 into the pilus structure requires SrtC1 and SrtC2, respectively. The S. agalactiae housekeeping sortase, SrtA, whose gene is present at a different location and does not catalyze pilus polymerization, was shown to be involved in cell wall anchoring of pilus polymers. To understand the structural basis of sortases involved in such diverse functions, we determined the crystal structures of S. agalactiae SrtC1 and SrtA. Both enzymes are made of an eight-stranded beta-barrel core with variations in their active site architecture. SrtA exhibits a catalytic triad arrangement similar to that in Streptococcus pyogenes SrtA but different from that in Staphylococcus aureus SrtA. In contrast, the SrtC1 enzyme contains an N-terminal helical domain and a ‘lid’ in its putative active site, which is similar to that seen in Streptococcus pneumoniae pilus-specific sortases, although with subtle differences in positioning and composition. To understand the effect of such differences on substrate recognition, we have also determined the crystal structure of a SrtC1 mutant, in which the conserved DP(W/F/Y) motif was replaced with the sorting signal motif of GBS80, IPNTG. By comparing the structures of WT wild type SrtA and SrtC1 and the ‘lid’ mutant of SrtC1, we propose that structural elements within the active site and the lid may be important for defining the role of specific sortase in pili biogenesis.

Structural determinants in streptococcal unsaturated glucuronyl hydrolase for recognition of glycosaminoglycan sulfate groups

Pathogenic Streptococcus agalactiae produces polysaccharide lyases and unsaturated glucuronyl hydrolase (UGL), which are prerequisite for complete degradation of mammalian extracellular matrices, including glycosaminoglycans such as chondroitin and hyaluronan. Unlike the Bacillus enzyme, streptococcal UGLs prefer sulfated glycosaminoglycans. Here, we show the loop flexibility for substrate binding and structural determinants for recognition of glycosaminoglycan sulfate groups in S. agalactiae UGL (SagUGL). UGL also degraded unsaturated heparin disaccharides; this indicates that the enzyme released unsaturated iduronic and glucuronic acids from substrates. We determined the crystal structures of SagUGL wild-type enzyme and both substrate-free and substrate-bound D175N mutants by x-ray crystallography and noted that the loop over the active cleft exhibits flexible motion for substrate binding. Several residues in the active cleft bind to the substrate, unsaturated chondroitin disaccharide with a sulfate group at the C-6 position of GalNAc residue. The sulfate group is hydrogen-bonded to Ser-365 and Ser-368 and close to Lys-370. As compared with wild-type enzyme, S365H, S368G, and K370I mutants exhibited higher Michaelis constants toward the substrate. The conversion of SagUGL to Bacillus sp. GL1 UGL-like enzyme via site-directed mutagenesis demonstrated that Ser-365 and Lys-370 are essential for direct binding and for electrostatic interaction, respectively, for recognition of the sulfate group by SagUGL. Molecular conversion was also achieved in SagUGL Arg-236 with an affinity for the sulfate group at the C-4 position of the GalNAc residue. These residues binding to sulfate groups are frequently conserved in pathogenic bacterial UGLs, suggesting that the motif "R-//-SXX(S)XK" (where the hyphen and slash marks in the motif indicate the presence of over 100 residues in the enzyme and parentheses indicate that Ser-368 makes little contribution to enzyme activity) is crucial for degradation of sulfated glycosaminoglycans.

The 2-Cys peroxiredoxin alkyl hydroperoxide reductase c binds heme and participates in its intracellular availability in Streptococcus agalactiae

Heme is a redox-reactive molecule with vital and complex roles in bacterial metabolism, survival, and virulence. However, few intracellular heme partners were identified to date and are not well conserved in bacteria. The opportunistic pathogen Streptococcus agalactiae (group B Streptococcus) is a heme auxotroph, which acquires exogenous heme to activate an aerobic respiratory chain. We identified the alkyl hydroperoxide reductase AhpC, a member of the highly conserved thiol-dependent 2-Cys peroxiredoxins, as a heme-binding protein. AhpC binds hemin with a K(d) of 0.5 microm and a 1:1 stoichiometry. Mutagenesis of cysteines revealed that hemin binding is dissociable from catalytic activity and multimerization. AhpC reductase activity was unchanged upon interaction with heme in vitro and in vivo. A group B Streptococcus ahpC mutant displayed attenuation of two heme-dependent functions, respiration and activity of a heterologous catalase, suggesting a role for AhpC in heme intracellular fate. In support of this hypothesis, AhpC-bound hemin was protected from chemical degradation in vitro. Our results reveal for the first time a role for AhpC as a heme-binding protein.

Genetic and biochemical modulation of sialic acid O-acetylation on group B Streptococcus: phenotypic and functional impact

Group B Streptococcus (GBS) is an important human pathogen and a model system for studying the roles of bacterial glycosylation in host-microbe interactions. Sialic acid (Sia), expressed prominently in the GBS capsular polysaccharide (CPS), mimics mammalian cell surface Sia and can interact with host Sia-binding proteins to subvert immune clearance mechanisms. Our earlier work has shown that GBS partially O-acetylates CPS Sia residues and employs an intracellular O-acetylation/de-O-acetylation cycle to control the final level of this surface Sia modification. Here, we examine the effects of point mutations in the NeuD O-acetyltransferase and NeuA O-acetylesterase on specific glycosylation phenotypes of GBS, pinpointing an isogenic strain pair that differs dramatically in the degree of the O-acetyl modification (80% versus 5%) while still expressing comparable levels of overall sialylation. Using these strains, higher levels of O-acetylation were found to protect GBS CPS Sia against enzymatic removal by microbial sialidases and to impede engagement of human Siglec-9, but not to significantly alter the ability of GBS to restrict complement C3b deposition on its surface. Additional experiments demonstrated that pH-induced migration of the O-acetyl modification from the 7- to 9-carbon position had a substantial impact on GBS-Siglec-9 interactions, with 7-O-acetylation exhibiting the strongest interference. These studies show that both the degree and position of the GBS O-acetyl modification influence Sia-specific interactions relevant to the host-pathogen relationship. We conclude that native GBS likely expresses a phenotype of intermediate Sia O-acetylation to strike a balance between competing selective pressures present in the host environment.

Substrate specificity of streptococcal unsaturated glucuronyl hydrolases for sulfated glycosaminoglycan

Unsaturated glucuronyl hydrolase (UGL) categorized into the glycoside hydrolase family 88 catalyzes the hydrolytic release of an unsaturated glucuronic acid from glycosaminoglycan disaccharides, which are produced from mammalian extracellular matrices through the beta-elimination reaction of polysaccharide lyases. Here, we show enzyme characteristics of pathogenic streptococcal UGLs and structural determinants for the enzyme substrate specificity. The putative genes for UGL and phosphotransferase system for amino sugar, a component of glycosaminoglycans, are assembled into a cluster in the genome of pyogenic and hemolytic streptococci such as Streptococcus agalactiae, Streptococcus pneumoniae, and Streptococcus pyogenes, which produce extracellular hyaluronate lyase as a virulent factor. The UGLs of these three streptococci were overexpressed in Escherichia coli cells, purified, and characterized. Streptococcal UGLs degraded unsaturated hyaluronate and chondroitin disaccharides most efficiently at approximately pH 5.5 and 37 degrees C. Distinct from Bacillus sp. GL1 UGL, streptococcal UGLs preferred sulfated substrates. DNA microarray and Western blotting indicated that the enzyme was constitutively expressed in S. agalactiae cells, although the expression level increased in the presence of glycosaminoglycan. The crystal structure of S. agalactiae UGL (SagUGL) was determined at 1.75 A resolution by x-ray crystallography. SagUGL adopts alpha(6)/alpha(6)-barrel structure as a basic scaffold similar to Bacillus UGL, but the arrangement of amino acid residues in the active site differs between the two. SagUGL Arg-236 was found to be one of the residues involved in its activity for the sulfated substrate through structural comparison and site-directed mutagenesis. This is the first report on the structure and function of streptococcal UGLs.

Crystallization and preliminary crystallographic analysis of bifunctional gamma-glutamylcysteine synthetase-glutatione synthetase from Streptococcus agalactiae

gamma-Glutamylcysteine synthetase-glutathione synthetase (gammaGCS-GS) is a bifunctional enzyme that catalyzes two consecutive steps of ATP-dependent peptide formation in glutathione biosynthesis. Streptococcus agalactiae gammaGCS-GS is a target for the development of potential therapeutic agents. gammaGCS-GS was crystallized using the sitting-drop vapour-diffusion method. The crystals grew to dimensions of 0.3 x 0.2 x 0.2 mm under reducing conditions with 5 mM TCEP. X-ray data were collected to 2.8 A resolution from a tetragonal crystal that belonged to space group I4(1).

Identification of serine/threonine kinase substrates in the human pathogen group B streptococcus

All living organisms respond to changes in their internal and external environment for their survival and existence. Signaling is primarily achieved through reversible phosphorylation of proteins in both prokaryotes and eukaryotes. A change in the phosphorylation state of a protein alters its function to enable the control of cellular responses. A number of serine/threonine kinases regulate the cellular responses of eukaryotes. Although common in eukaryotes, serine/threonine kinases have only recently been identified in prokaryotes. We have described that the human pathogen Group B Streptococcus (GBS, Streptococcus agalactiae) encodes a single membrane-associated, serine/threonine kinase (Stk1) that is important for virulence of this bacterium. In this study, we used a combination of phosphopeptide enrichment and mass spectrometry to enrich and identify serine (S) and threonine (T) phosphopeptides of GBS. A comparison of S/T phosphopeptides identified from the Stk1 expressing strains to the isogenic stk1 mutant indicates that 10 proteins are potential substrates of the GBS Stk1 enzyme. Some of these proteins are phosphorylated by Stk1 in vitro and a site-directed substitution of the phosphorylated threonine to an alanine abolished phosphorylation of an Stk1 substrate. Collectively, these studies provide a novel approach to identify serine/threonine kinase substrates for insight into their signaling in human pathogens like GBS.

Functional characterization of a newly identified group B Streptococcus pullulanase eliciting antibodies able to prevent alpha-glucans degradation

Streptococcal pullulanases have been recently proposed as key components of the metabolic machinery involved in bacterial adaptation to host niches. By sequence analysis of the Group B Streptococcus (GBS) genome we found a novel putative surface exposed protein with pullulanase activity. We named such a protein SAP. The sap gene is highly conserved among GBS strains and homologous genes, such as PulA and SpuA, have been described in other pathogenic streptococci. The SAP protein contains two N-terminal carbohydrate-binding motifs, followed by a catalytic domain and a C-terminal LPXTG cell wall-anchoring domain. In vitro analysis revealed that the recombinant form of SAP is able to degrade α-glucan polysaccharides, such as pullulan, glycogen and starch. Moreover, NMR analysis showed that SAP acts as a type I pullulanase. Studies performed on whole bacteria indicated that the presence of α-glucan polysaccharides in culture medium up-regulated the expression of SAP on bacterial surface as confirmed by FACS analysis and confocal imaging. Deletion of the sap gene resulted in a reduced capacity of bacteria to grow in medium containing pullulan or glycogen, but not glucose or maltose, confirming the pivotal role of SAP in GBS metabolism of α-glucans. As reported for other streptococcal pullulanases, we found specific anti-SAP antibodies in human sera from healthy volunteers. Investigation of the functional role of anti-SAP antibodies revealed that incubation of GBS in the presence of sera from animals immunized with SAP reduced the capacity of the bacterium to degrade pullulan. Of interest, anti-SAP sera, although to a lower extent, also inhibited Group A Streptococcus pullulanase activity. These data open new perspectives on the possibility to use SAP as a potential vaccine component inducing functional cross-reacting antibodies interfering with streptococcal infections.

Anti-atherosclerotic effect of microbial hyaluronate lyase from group B streptococci

The effect of the microbial hyaluronic acid splitting enzyme hyaluronate lyase produced by Streptococcus agalactiae was investigated in vitro in human atherosclerotic plaque specimens and in vivo on Watanabe heritable hyperlipidaemic rabbits (WHHL) as an animal model for familiar hypercholesteraemia. The in vitro presence of the enzyme caused a partial destruction of the atherosclerotic plaque surfaces as well as releasing of glucuronic acid and solid calcium-containing materials from pieces of atherosclerotic plaques in human arteries. Accordingly hyaluronic acid seems to be the main component for anchoring of calcium deposits on the plaque surfaces. Repeated intravenous injections of hyaluronate lyase in WHHL rabbits resulted in a tendency of decreased formation of atherosclerotic plaques. The observed effects are discussed to be primary the result of the splitting of hyaluronic acid in the vessels.

Metallopeptidases produced by group B Streptococcus: influence of proteolytic inhibitors on growth and on interaction with human cell lineages

Group B Streptococcus (GBS) is a major etiologic agent of neonatal bacterial infections and is the most common cause of sepsis and pneumonia in newborns. Surface and secreted molecules of GBS are often essential virulence factors which are involved in the adherence of the bacteria to host cells or are required to suppress the defense mechanisms of hosts. We analyzed the peptidase profiles of GBS by detection of proteolytic activities on SDS-PAGE containing copolymerized gelatin as substrate. Based on the inhibition by o-phenathroline and EGTA, three distinct peptidases of 220, 200 and 180 kDa were identified in the culture medium, besides one major cell-associated proteolytic activity, a 200-kDa metallopeptidase, suggesting that all were zinc-metallopeptidases. GBS culture supernatants, rich in metallotype peptidases, also cleaved fibronectin, laminin, type IV collagen, fibrinogen and albumin. Cleavage of the host extracellular matrix by GBS may be a relevant factor in the process of bacterial dissemination and/or invasion. Notably, metallopeptidase inhibitors strongly blocked GBS growth as well as its interaction with human cell lineages. Understanding the contribution of peptidases to the pathogenesis of GBS disease may broaden our perception of how this significant pathogen causes severe infections in newborn infants.

A streptococcal penicillin-binding protein is critical for resisting innate airway defenses in the neonatal lung

Group B streptococcus (GBS) is a major cause of neonatal pneumonia. The early interactions between innate airway defenses and this pathogen are likely to be a critical factor in determining the outcome for the host. The surface-localized penicillin-binding protein (PBP)1a, encoded by ponA, is known to be an important virulence trait in a sepsis model of GBS infection that promotes resistance to neutrophil killing and more specifically to neutrophil antimicrobial peptides (AMPs). In this study, we used an aerosolization model to explore the role of PBP1a in evasion of innate immune defenses in the neonatal lung. The ponA mutant strain was cleared more rapidly from the lungs of neonatal rat pups compared with the wild-type strain, which could be linked to a survival defect in the presence of alveolar macrophages (AM). Rat AM were found to secrete beta-defensin and cathelicidin AMP homologues, and the GBS ponA mutant was more susceptible than the wild-type strain to killing by these peptides in vitro. Collectively, our observations suggest that PBP1a-mediated resistance to AM AMPs promotes the survival of GBS in the neonatal lung. Additionally, AM are traditionally thought to clear bacteria through phagocytic uptake; our data indicate that secretion of AMPs may also participate in limiting bacterial replication in the airway.

Détection de la colonisation par Streptococcus agalactiae: étude prospective comparant l'amplification génique en temps réel à un nouveau milieu chromogène Strepto B ID

We carried out a prospective study including 554 vaginal swabs simultaneously tested for antenatal screening of Group B Streptococcus (GBS or Streptococcus agalactiae) using culture on the chromogenic medium Strepto B ID (Biomérieux, Marcy l'Etoile, France) and real time gene amplification on LightCycler (Roche Applied Science). We centrifuge the swabs with "SETS" device and separate centrifugates in 2 parts: one for the culture and the other one for molecular biology. First half of the centrifugate is inoculated onto Todd-Hewitt broth enriched with antibiotics. This broth is incubated to 35 degrees C during 24 hours and then subcultured on a Strepto B ID medium. This last one is incubated during 24 hours to 35 degrees C in capnophilic conditions before interpretation. DNA extraction for molecular biology is simply obtained by heating the microtubes to 95 degrees C in a water bath. The cfb gene is amplified, allowing a specific gene amplification of GBS even within a polymorphic flora. The concordance between both methods is 94.8%. The sensitivity and negative predictive values obtained are respectively 88.0 and 97.4% for real time PCR and 83.0 and 96.4% for culture on Strepto B ID. Both methods are thus concordant, with equal sensitivity and valid for detection of GBS colonization in pregnant women. However real time gene amplification allows reducing turn around time since molecular biology process (extraction+amplification) does not exceed 1 hour.

Structure of the Streptococcus agalactiae family II inorganic pyrophosphatase at 2.80 A resolution

Streptococcus agalactiae, a prokaryote that causes infections in neonates and immunocompromised adults, has a serine/threonine protein kinase (STK) signalling cascade. The structure of one of the targets, a family II inorganic pyrophosphatase, has been solved by molecular replacement and refined at 2.80 A resolution to an R factor of 19.2% (R(free) = 26.7%). The two monomers in the asymmetric unit are related by a noncrystallographic twofold axis, but the biological dimer is formed by a crystallographic twofold. Each monomer contains the pyrophosphate analogue imidodiphosphate (PNP) and three metal ions per active site: two Mn(2+) ions in sites M1 and M2 and an Mg(2+) ion in site M3. The enzyme is in the closed conformation. Like other family II enzymes, the structure consists of two domains (residues 1-191 and 198-311), with the active site located between them. The conformation of Lys298 in the active site is different from those observed previously and it coordinates to the conserved DHH motif in a unique way. The structure suggests that Ser150, Ser194, Ser195 and Ser296 are the most likely targets for the Ser/Thr kinase and phosphatase because they are surface-accessible and either in the active site or in the hinge region between the two domains.

Structure of Streptococcus agalactiae serine/threonine phosphatase. The subdomain conformation is coupled to the binding of a third metal ion

We solved the crystal structure of Streptococcus agalactiae serine/threonine phosphatase (SaSTP) using a combination of single-wavelength anomalous dispersion phasing and molecular replacement. The overall structure resembles that of previously characterized members of the PPM/PP2C STP family. The asymmetric unit contains four monomers and we observed two novel conformations for the flap domain among them. In one of these conformations, the enzyme binds three metal ions, whereas in the other it binds only two. The three-metal ion structure also has the active site arginine in a novel conformation. The switch between the two- and three-metal ion structures appears to be binding of another monomer to the active site of STP, which promotes binding of the third metal ion. This interaction may mimic the binding of a product complex, especially since the motif binding to the active site contains a serine residue aligning remarkably well with the phosphate found in the human STP structure.

Streptococcus agalactiae GAPDH is a virulence-associated immunomodulatory protein

Certain extracellular proteins produced by several pathogenic microorganisms interfere with the host immune system facilitating microbial colonization and were thus designated virulence-associated immunomodulatory proteins. In this study, a protein with B lymphocyte stimulatory activity was isolated from culture supernatants of Streptococcus agalactiae strain NEM316. This protein, with an apparent molecular mass of 45 kDa, was identified as GAPDH by N-terminal amino acid sequencing. The gapC gene was cloned and expressed in Escherichia coli for the production of a recombinant histidyl-tagged protein. The recombinant GAPDH (rGAPDH), purified in an enzymatically active form, induced in vitro an up-regulation of CD69 expression on B cells from normal and BCR transgenic mice. In addition, rGAPDH induced an increase in the numbers of total, but not of rGAPDH-specific, splenic Ig-secreting cells in C57BL/6 mice treated i.p. with this protein. These in vitro- and in vivo-elicited B cell responses suggest that the B cell stimulatory effect of rGAPDH is independent of BCR specificity. A S. agalactiae strain overexpressing GAPDH showed increased virulence as compared with the wild-type strain in C57BL/6 mice. This virulence was markedly reduced in IL-10-deficient and anti-rGAPDH antiserum-treated mice. These results suggest that IL-10 production, which was detected at higher concentrations in the serum of rGAPDH-treated mice, is important in determining the successfulness of the host colonization by S. agalactiae and they highlight the direct role of GAPDH in this process. Taken together, our data demonstrate that S. agalactiae GAPDH is a virulence-associated immunomodulatory protein.

Role of ionic interactions and linker in the domain interaction and modulation of functional activity of hyaluronate lyases

Hyaluronate lyases from Streptococcus pneumoniae (SpnHL) and Streptococcus agalactiae (SagHL) are composed of four domains; N-terminal domain, spacer domain, alpha-domain and C-terminal domain, which are connected through peptide linkers. We have earlier shown that the recombinant alpha- and C-terminal domains of SpnHL/SagHL interact with each other even in absence of the linker and form a functional complex with enhanced enzymatic activity. Here, we looked into the role of ionic interactions in the enzyme stability and also the role of C-terminal domain and linker in the functional regulation. Domain swapping studies showed that the C-terminal domain does not bind directly to the substrate; instead the domain contributes to the interaction with the polymeric hyaluronan for catalysis. Furthermore, the substrate specificity exchanges with the size of catalytic cleft. The role of linker connecting alpha-domain to C-terminal domain was found to hold the C-terminal domain in a conformation suitable for achieving maximum activity.

High-affinity interaction between fibronectin and the group B streptococcal C5a peptidase is unaffected by a naturally occurring four-amino-acid deletion that eliminates peptidase activity

The streptococcal C5a peptidase (ScpB) of group B streptococci (GBS) is found in virtually all clinical GBS isolates and is required for mucosal colonization in a neonatal mouse model. ScpB inhibits neutrophil chemotaxis by enzymatically cleaving the complement component C5a. We previously identified a second function of ScpB as a fibronectin (Fn) adhesin using phage display. However, phage display can identify low-affinity interactions. We therefore measured the affinity of both full-length recombinant ScpB (FL-ScpB) and the 110-amino-acid phage display fragment (Scp-PDF) for immobilized Fn using surface plasmon resonance. The affinity for Fn was very high for both FL-ScpB (equilibrium dissociation constant [KD] = 4.0 nM) and Scp-PDF (KD = 4.4 nM) and is consistent with a biologically significant role for the adhesin activity of ScpB. We also studied the Fn adhesin activity of a common natural variant of ScpB (ScpBDelta) that contains a 4-amino-acid deletion that eliminates peptidase activity. The integrity of scpB is otherwise maintained, suggesting that the Fn adhesin activity of ScpB may be responsible for its conservation in these strains. The affinities of both FL-ScpBDelta (KD = 2.4 nM) and ScpBDelta-PDF (KD = 1.4 nM) for Fn are unaffected by the deletion. Complementation in trans by both scpB and scpBDelta corrected the Fn-binding defect of an scpB deletion mutant GBS strain to an identical degree. The high affinity of ScpB for Fn and the maintenance of this affinity in ScpBDelta support our hypothesis that the Fn adhesin activity of scpB plays a role in virulence.

Novel substrate specificity of glutathione synthesis enzymes from Streptococcus agalactiae and Clostridium acetobutylicum

Glutathione (GSH) is synthesized by gamma-glutamylcysteine synthetase (gamma-GCS) and glutathione synthetase (GS) in living organisms. Recently, bifunctional fusion protein, termed gamma-GCS-GS catalyzing both gamma-GCS and GS reactions from gram-positive firmicutes Streptococcus agalactiae, has been reported. We revealed that in the gamma-GCS activity, S. agalactiae gamma-GCS-GS had different substrate specificities from those of Escherichia coli gamma-GCS. Furthermore, S. agalactiae gamma-GCS-GS synthesized several kinds of gamma-glutamyltripeptide, gamma-Glu-X(aa)-Gly, from free three amino acids. In Clostridium acetobutylicum, the genes encoding gamma-GCS and putative GS were found to be immediately adjacent by BLAST search, and had amino acid sequence homology with S. agalactiae gamma-GCS-GS, respectively. We confirmed that the proteins expressed from each gene showed gamma-GCS and GS activity, respectively. C. acetobutylicum GS had broad substrate specificities and synthesized several kinds of gamma-glutamyltripeptide, gamma-Glu-Cys-X(aa). Whereas the substrate specificities of gamma-GCS domain protein and GS domain protein of S. agalactiae gamma-GCS-GS were the same as those of S. agalactiae gamma-GCS-GS.

Gamma-glutamylcysteine synthetase-glutathione synthetase: domain structure and identification of residues important in substrate and glutathione binding

In most organisms, glutathione (GSH) is synthesized by the sequential action of distinct enzymes, gamma-glutamylcysteine synthetase (gamma-GCS) and GSH synthetase (GS). In Streptococcus agalactiae, GSH synthesis is catalyzed by a single enzyme, gamma-glutamylcysteine synthetase-glutathione synthetase (gamma-GCS-GS). The N-terminal sequence of gamma-GCS-GS is similar to Escherichia coli gamma-GCS, but the C-terminal sequence is an ATP-grasp domain more similar to d-Ala, d-Ala ligase than to any known GS. In the present studies, C-terminally and N-terminally truncated constructs were characterized in order to define the limits of the gamma-GCS and GS domains, respectively. Although WT gamma-GCS-GS is nearly uninhibited by GSH (K(i) approximately 140 mM), shorter gamma-GCS domain constructs were unexpectedly found to be strongly inhibited (K(i) approximately 15 mM), reproducing a physiologically important regulation seen in monofunctional gamma-GCS enzymes. Because studies with E. coli gamma-GCS implicate a flexible loop region in GSH binding, chimeras of S. agalactiae gamma-GCS-GS were made containing gamma-GCS domain flexible loop sequences from Enterococcus faecalis and Pasteurella multocida gamma-GCS-GS, isoforms that are inhibited by GSH. Inhibition remained S. agalactiae-like (i.e., very weak). C-Terminal constructs of gamma-GCS-GS have GS activity (0.01-0.04% of WT), but proper folding and significant GS activity required a covalently linked gamma-GCS domain. In addition, site-directed mutants in the middle region of the gamma-GCS-GS sequence established that GS activity depends on residues in a region that is also part of the gamma-GCS domain. Our results provide new insights into the structure of gamma-GCS-GS and suggest gamma-GCS-GS evolved from a monomeric gamma-GCS that became C-terminally fused to a multimeric ATP-grasp protein.

Novel 6-O-acylated vitamin C derivatives as hyaluronidase inhibitors with selectivity for bacterial lyases

Previously, we identified ascorbic acid 6-O-hexadecanoate as an up to 1500 times more potent inhibitor of bacterial and bovine hyaluronidases than the parent compound, vitamin C, and determined a crystal structure of hyaluronidase from Streptococcus pneumoniae in complex with the inhibitor. As the alkanoyl chain interacts with a hydrophobic patch of the enzyme we synthesized other 6-O-acylated vitamin C derivatives bearing various lipophilic residues and investigated the inhibition of Streptococcus agalactiae strain 4755 hyaluronidase (SagHyal(4755)) and of bovine testicular hyaluronidases (BTH) in a turbidimetric assay. All compounds showed selectivity for the bacterial enzyme. Whereas vitamin C 6-O-hexanoate only weakly inhibited SagHyal(4755), the inhibition of both enzymes increased with the length of the aliphatic chain. In the case of the 6-O-octadecanoate, IC(50) values of 0.9 and 39microM for SagHyal(4755) and BTH, respectively, were determined. Partial replacement of the aliphatic chain with a phenyl, p-phenylene or p-biphenylyl group resulted in inhibitors with activity in the lower micromolar range, too. The title compounds are among the most potent inhibitors of both enzymes known to date.

Insights into the Mechanism of Action of Hyaluronate Lyase

Hyaluronate lyases (HLs) cleave hyaluronan and certain other chondroitin/chondroitin sulfates. Although native HL from Streptococcus agalactiae is composed of four domains, it finally stabilizes after autocatalytic conversion as a 92-kDa enzyme composed of the N-terminal spacer, middle alpha-, and C-terminal domains. These three domains are independent folding/unfolding units of the enzyme. Comparative structural and functional studies using the enzyme and its various fragments/domains suggest a relatively insignificant role of the N-terminal spacer domain in the 92-kDa enzyme. Functional studies demonstrate that the alpha-domain is the catalytic domain. However, independently it has a maximum of only about 10% of the activity of the 92-kDa enzyme, whereas its complex with the C-terminal domain in vitro shows a significant enhancement (about 6-fold) in the activity. It has been previously proposed that the C-terminal domain modulates the enzymatic activity of HLs. In addition, one of the possible roles for calcium ions was suggested to induce conformational changes in the enzyme loops, making HL more suitable for catalysis. However, we observed that calcium ions do not interact with the enzyme, and its role actually is in modulating the hyaluronan conformation and not in the functional regulation of enzyme.

Crystallization and preliminary crystallographic analysis of two Streptococcus agalactiae proteins: the family II inorganic pyrophosphatase and the serine/threonine phosphatase

Streptococcus agalactiae, which infects human neonates and causes sepsis and meningitis, has recently been shown to possess a eukaryotic-like serine/threonine protein phosphorylation signalling cascade. Through their target proteins, the S. agalactiae Ser/Thr kinase and Ser/Thr phosphatase together control the growth as well as the morphology and virulence of this organism. One of the targets is the S. agalactiae family II inorganic pyrophosphatase. The inorganic pyrophosphatase and the serine/threonine phosphatase have therefore been purified and crystallized and diffraction data have been collected from their crystals. The data were processed using XDS. The inorganic pyrosphosphatase crystals diffracted to 2.80 A and the Ser/Thr phosphatase crystals to 2.65 A. Initial structure-solution experiments indicate that structure solution will be successful in both cases. Solving the structure of the proteins involved in this cascade is the first step towards understanding this phenomenon in atomic detail.

[Use of hyaluronic acid cleaving enzymes for absorption acceleration. Results of an in vitro study with xylazine and ketamine]

The so-called "Hellabrunner Mischung", (combination of xylazine and ketamine with hyaluronidase) is frequently used for the immobilisation of wildlife animals. The enzyme hyaluronidase shall improve the distribution of the intramuscularly or subcutaneously administered compounds in the tissue and enhance their absorption. These enhancing effects of two hyaluronate lyases of bacterial origin (Streptococcus agalactiae and Streptococcus equisimilis) and a testicular hyaluronidase were compared in an in vitro test. Using the isolated perfused bovine udder, 2 ml of a solution were administered subcutaneously containing 125 mg/ml xylazine and 100 mg/ml ketamine and one of the above mentioned enzymes (150 I.U.). All three enzymes enhanced the absorption rate of xylazine and ketamine determined by measurement of the concentration in the perfusate. The bacterial hyaluronate lyases were significantly more efficient, especially during the clinically important first minutes after administration.

Characterization of a bifunctional cytidine 5'-monophosphate N-acetylneuraminic acid synthetase cloned from Streptococcus agalactiae

Recombinant CMP-sialic acid synthetase, cloned from Streptococcus agalactiae serotype V strain 2603 V/R, is bifunctional having both CMP-sialic acid synthetase and acetylhydrolase (acylesterase) activities. The enzyme is active over a wide pH range with an optimal CMP-sialic acid synthetase activity at pH 9.0 and an optimal acetylhydrolase activity at pH 8.0. A metal cofactor (either Mg(2+) or Mn(2+)) is required for the CMP-sialic acid synthetase activity but is not for acetylhydrolase activity. Both catalytic functions, however, are impaired by high concentrations of Mn(2+).

Inhibitory Effects of Triterpenes and Flavonoids on the Enzymatic Activity of Hyaluronic Acid-Splitting Enzymes

The effect of triterpenes and flavonoids on the activity of several hyaluronic acid-splitting enzymes was investigated. Studies showed that the inhibitory effect of the triterpenes glycyrrhizin and glycyrrhetinic acid is dependent on the source of hyaluronate lyase. Hyaluronate lyase from Streptococcus agalactiae (Hyal B) and recombinant hyaluronate lyase from Streptococcus agalactiae (rHyal B) demonstrated strongest inhibition. In contrast, hyaluronate lyases from Streptomyces hyalurolyticus (Hyal S), Streptococcus equisimilis (Hyal C) and hyaluronidase from bovine testis (Dase) showed only reduced inhibition action. A non-competitive dead end inhibition with Ki=3.1+/-1.8x10(-6) mol/mL and Kii=6.7+/-2.4x10(-6) mol/mL was found for glycyrrhizin on recombinant hyaluronate lyase from Streptococcus agalactiae. The inhibitory effect of flavonoids on Hyal B, rHyal B and Dase was determined depending on the number of hydroxyl groups and side chain substituents in the molecule. Flavonoids with many hydroxyl groups inhibited hyaluronate lyase stronger than those with only a few. Native hyaluronate lyase (Hyal B) showed a more extensive inhibition than the recombinant protein (rHyal B). Accordingly, the inhibition by triterpenes and flavonoids is presumably specific for each hyaluronic acid (HA)-splitting enzyme.

Alternate structural conformations of Streptococcus pneumoniae hyaluronan lyase: insights into enzyme flexibility and underlying molecular mechanism of action

Streptococcus pneumoniae hyaluronan lyase is a surface enzyme of this Gram-positive bacterium. The enzyme degrades several biologically important, information-rich linear polymeric glycans: hyaluronan, unsulfated chondroitin, and some chondroitin sulfates. This degradation facilitates spreading of bacteria throughout the host tissues and presumably provides energy and a carbon source for pneumococcal cells. Its beta-elimination catalytic mechanism is an acid/base process termed proton acceptance and donation leading to cleavage of beta-1,4 linkages of the substrates. The degradation of hyaluronan occurs in two stages, initial endolytic cuts are followed by processive exolytic cleavage of one disaccharide at a time. In contrast, the degradation of chondroitins is purely endolytic. Structural studies together with flexibility analyses of two streptococcal enzymes, from S.pneumoniae and Streptococcus agalactiae, allowed for insights into this enzyme's molecular mechanism. Here, two new X-ray crystal structures of the pneumococcal enzyme in novel conformations are reported. These new conformations, complemented by molecular dynamics simulation results, directly confirm the predicted domain motions presumed to facilitate the processive degradative process. One of these new structures resembles the S.agalactiae enzyme conformation, and provides evidence of a uniform mechanistic/dynamic behavior of this protein across different bacteria.

Structure of the streptococcal cell wall C5a peptidase

The structure of a cell surface enzyme from a gram-positive pathogen has been determined to 2-A resolution. Gram-positive pathogens have a thick cell wall to which proteins and carbohydrate are covalently attached. Streptococcal C5a peptidase (SCP), is a highly specific protease and adhesin/invasin. Structural analysis of a 949-residue fragment of the [D130A,S512A] mutant of SCP from group B Streptococcus (S. agalactiae, SCPB) revealed SCPB is composed of five distinct domains. The N-terminal subtilisin-like protease domain has a 134-residue protease-associated domain inserted into a loop between two beta-strands. This domain also contains one of two Arg-Gly-Asp (RGD) sequences found in SCPB. At the C terminus are three fibronectin type III (Fn) domains. The second RGD sequence is located between Fn1 and Fn2. Our analysis suggests that SCP binding to integrins by the RGD motifs may stabilize conformational changes required for substrate binding.

New lnu(C) gene conferring resistance to lincomycin by nucleotidylation in Streptococcus agalactiae UCN36

Streptococcus agalactiae UCN36 was resistant to lincomycin (MIC = 16 microg/ml) but susceptible to clindamycin (MIC = 0.12 microg/ml) and erythromycin (MIC = 0.06 microg/ml). A 4-kb HindIII fragment was cloned from S. agalactiae UCN36 total DNA on plasmid pUC18 and introduced into Escherichia coli AG100A, where it conferred resistance to lincomycin. The sequence analysis of the fragment showed the presence of a 1,724-bp element delineated by imperfect inverted repeats (22 of 25 bp) and inserted in the operon for capsular synthesis of S. agalactiae UCN36. This element carried two open reading frames (ORF). The deduced amino acid sequence of the upstream ORF displayed similarity with transposases from anaerobes and IS1. The downstream ORF, lnu(C), encoded a 164-amino-acid protein with 26% to 27% identity with the LnuA(N2), LnuA, and LnuA' lincosamide nucleotidyltransferases reported for Bacteroides and Staphylococcus, respectively. Crude lysates of E. coli AG100A containing the cloned lnu(C) gene inactivated lincomycin and clindamycin in the presence of ATP and MgCl2. Mass spectrometry experiments demonstrated that the LnuC enzyme catalyzed adenylylation of lincomycin.

Sulphated oligosaccharides as inhibitors of hyaluronidases from bovine testis, bee venom and Streptococcus agalactiae

Potent and specific inhibitors of hyaluronidases, a group of enzymes preferentially catalysing the hydrolysis of hyaluronic acid, are not known so far. Such compounds could be useful as pharmacological tools for studying the physiological and pathophysiological role of both hyaluronan and hyaluronidases. The effects of sulphated and non-sulphated structurally different oligosaccharides on bovine testicular hyaluronidase, hyaluronidase from bee venom and hyaluronate lyase from Streptococcus agalactiae (hylB (4755)) were studied with the Morgan-Elson reaction. Several active compounds were identified within a series of sulphated beta-(1,4)-galacto-oligosaccharides. The determined IC (50) values of these sulphated oligosaccharides ranged from 4 microM to 630 microM for all hyaluronan-degrading enzymes. Sulphated oligosaccharides like verbascose, planteose and neomycin showed comparable inhibition on all hyaluronidases, thereby possessing 100 - 500 times the activity of the widely accepted hyaluronidase inhibitor apigenin.

Molecular subtyping and characterization of bovine and human Streptococcus agalactiae isolates

Streptococcus agalactiae causes severe invasive disease in humans and mastitis in cattle. Temporally matched bovine milk isolates and clinical human invasive isolates (52 each) collected in New York State over 18 months were characterized by molecular subtyping and phenotypic methods to probe the interspecies transmission potential of this species. EcoRI ribotyping differentiated 17 ribotypes, and DNA sequencing of the housekeeping gene sodA and the putative virulence gene hylB differentiated 7 and 17 allelic types, respectively. Human and bovine isolates were not randomly distributed between ribotypes or hylB and sodA clusters. The combined analysis of all subtyping data allowed the differentiation of 39 clonal groups; 26 groups contained only bovine isolates, and 2 groups contained both human and bovine isolates. The EcoRI ribotype diversity among bovine isolates (Simpson's numerical index of discrimination [mean +/- standard deviation], 0.90 +/- 0.05) being significantly higher than that among human isolates (0.42 +/- 0.15) further supports that these isolates represent distinct populations. Eight human isolates, but no bovine isolates, showed an IS1548 transposon insertion in hylB, which encodes a hyaluronidase. Based on data for 43 representative isolates, human isolates, on average, showed lower hyaluronidase activities than bovine isolates. Isolates with the IS1548 insertion in hylB showed no hyaluronidase activity. Human and bovine isolates did not differ in their abilities to invade HeLa human epithelial cells. Our data show that (i) EcoRI ribotyping, combined with hylB and sodA sequencing, provides a discriminatory subtype analysis of S. agalactiae; (ii) most human invasive and bovine S. agalactiae isolates represent distinct subtypes, suggesting limited interspecies transmission; and (iii) hyaluronidase activity is not required for all human infections.

Crystal structure of the N-terminal domain of the group B streptococcus alpha C protein

Group B Streptococcus (GBS) is the leading cause of bacterial pneumonia, sepsis, and meningitis among neonates and an important cause of morbidity among pregnant women and immunocompromised adults. Invasive diseases due to GBS are attributed to the ability of the pathogen to translocate across human epithelial surfaces. The alpha C protein (ACP) has been identified as an invasin that plays a role in internalization and translocation of GBS across epithelial cells. The soluble N-terminal domain of ACP (NtACP) blocks the internalization of GBS. We determined the 1.86-A resolution crystal structure of NtACP comprising residues Ser(52) through Leu(225) of the full-length ACP. NtACP has two domains, an N-terminal beta-sandwich and a C-terminal three-helix bundle. Structural and topological alignments reveal that the beta-sandwich shares structural elements with the type III fibronectin fold (FnIII), but includes structural elaborations that make it unique. We have identified a potential integrin-binding motif consisting of Lys-Thr-Asp(146), Arg(110), and Asp(118). A similar arrangement of charged residues has been described in other invasins. ACP shows a heparin binding activity that requires NtACP. We propose a possible heparin-binding site, including one surface of the three-helix bundle, and nearby portions of the sandwich and repeat domains. We have validated this prediction using assays of the heparin binding and cell-adhesion properties of engineered fragments of ACP. This is the first crystal structure of a member of the highly conserved Gram-positive surface alpha-like protein family, and it will enable the internalization mechanism of GBS to be dissected at the atomic level.

ISSag1 in streptococcal strains of human and animal origin

The chromosomal region of Streptococcus agalactiae harboring the C5a peptidase and the lmb genes displays the structure of a composite transposon. Its presence in a streptococcal strain is associated with the origin of this strain from a human host. In S. agalactiae it is flanked by two copies of the insertion element ISSag2, and the nucleotide sequence for a third IS element (ISSag1) can be found in this region. Based on amino acid sequence similarity of the deduced transposase ISSag1 belongs to the IS3 family. It is 1251 bp long and flanked by 37 bp imperfect inverted repeats. Horizontal gene transfer among different bacterial species is facilitated by mobile genetic elements. To investigate if ISSag1 homologues are also present in other streptococcal species, various species of pyogenic streptococci from animal and human origin were analyzed by Southern blot hybridization and PCR. Among the different streptococcal species, multiple copies of an ISSag1 homologue could only be detected in S. dysgalactiae subsp. dysgalactiae strains of animal origin. All of the S. agalactiae strains harbored only a single copy, that was always found in strains with the scpB-lmb composite transposon. A single copy of an ISSag1 homologue could also be detected in some of the S. pyogenes and S. dysgalactiae subsp. equisimilis strains. Nucleotide sequencing of the IS element in S. dysgalactiae subsp. dysgalactiae strains revealed several different variants. One of the variants showed the features of a regular IS3 element. The other two variants that were observed displayed a 500-bp deletion and a mosaic structure composed of ISSag1 and ISSag2 homologues. This mosaic structure suggests that recombination and horizontal gene transfer events in S. dysgalactiae strains of bovine origin could have played a role in the assembly of the scpB-lmb composite transposon structure.

Complementary exploration of the action pattern of hyaluronate lyase from Streptococcus agalactiae using capillary electrophoresis, gel-permeation chromatography and viscosimetric measurements

Hyaluronic acid (HA) was treated with hyaluronate lyase (GBS HA lyase, E.C. 4.2.2.1, from Streptococcus agalactiae strain 4755), and the products have been analyzed by capillary electrophoresis (CE-UV and online CE-ESIMS), gel-permeation chromatography (GPC) and viscosimetric measurements. The resulting electropherograms showed that the enzyme produced a mixture of oligosaccharides with a 4,5-unsaturated uronic acid nonreducing terminus. More exhaustive degradation of HA led to increasing amounts of di-, tetra-, hexa-, octa- and decasaccharides. Using CE, linear relationships were found between peak area of the observed oligosaccharides and reaction time. Determination of viscosity at different stages of reaction yielded an initial rapid decrease following Michaelis-Menten theory. A reaction time-dependent change in the elution position of the HA peak due to partial digestion of HA with GBS hyaluronate lyase has been observed by GPC. These results indicated that the HA lyase under investigation is an eliminase that acts in a nonprocessive endolytic manner, as at all stages of digestion a mixture of oligosaccharides of different size were found. For GBS HA lyase from Streptococcus agalactiae strain 3502, previously published findings reported an action pattern that involves an initial random endolytic cleavage followed by rapid exolytic and processive release of unsaturated disaccharides. Our results suggest that differences between the two enzymes from distinct S. agalactiae strains (GBS strains 4755 and 3502) have to be considered.

l-Ascorbic Acid 6-Hexadecanoate, a Potent Hyaluronidase Inhibitor

Hyaluronidases are enzymes that degrade hyaluronan, an important component of the extracellular matrix. The mammalian hyaluronidases are considered to be involved in many (patho)physiological processes like fertilization, tumor growth, and metastasis. Bacterial hyaluronidases, also termed hyaluronate lyases, contribute to the spreading of microorganisms in tissues. Such roles for hyaluronidases suggest that inhibitors could be useful pharmacological tools. Potent and selective inhibitors are not known to date, although L-ascorbic acid has been reported to be a weak inhibitor of Streptococcus pneumoniae hyaluronate lyase (SpnHL). The x-ray structure of SpnHL complexed with L-ascorbic acid has been elucidated suggesting that additional hydrophobic interactions might increase inhibitory activity. Here we show that L-ascorbic acid 6-hexadecanoate (Vcpal) is a potent inhibitor of both streptococcal and bovine testicular hyaluronidase (BTH). Vcpal showed strong inhibition of Streptococcus agalactiae hyaluronate lyase with an IC(50) of 4 microM and weaker inhibition of SpnHL and BTH with IC(50) values of 100 and 56 microM, respectively. To date, Vcpal has proved to be one of the most potent inhibitors of hyaluronidase. We also determined the x-ray structure of the SpnHL-Vcpal complex and confirmed the hypothesis that additional hydrophobic interactions with Phe-343, His-399, and Thr-400 in the active site led to increased inhibition. A homology structural model of BTH was also generated to suggest binding modes of Vcpal to this hyaluronidase. The long alkyl chain seemed to interact with an extended, hydrophobic channel formed by mostly conserved amino acids Ala-84, Leu-91, Tyr-93, Tyr-220, and Leu-344 in BTH.

Bacterial Capsular Polysaccharide and Sugar Transferases

Capsular polysaccharides (CPs) of several pathogenic bacteria are thought to be good materials for the development of new therapeutic reagents. These polysaccharides can be used as vaccines against infection of pathogenic bacteria and are also useful as inhibitors for disease caused by aberrant and abnormal cell-cell interaction, such as cancer metastasis and inflammation. Since bacterial CPs are diverse in structure and these bacteria have a variety of sugar transferases responsible for the synthesis of CPs, bacterial CP synthesis (cps) genes have attracted much interest as a source of glycosyltransferases useful for glycoengineering. In this review, we describe physiological effects of the bacterial CPs on mammalian cells, and the structure and function of the cps genes, by focusing on group B streptococci, Streptococcus agalactiae type Ia and Ib, that produce high-molecular weight polysaccharides consisting of the following pentasaccharide repeating units: -->4)-[alpha-D-NeupNAc-(2-->3)-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->3)]-beta-D-Galp-(1-->4)-beta-D-Glcp-(1--> and -->4)-[alpha-D-NeupNAc-(2-->3)-beta-D-Galp-(1-->3)-beta-D-GlcpNAc-(1-->3)]-beta-D-Galp-(1-->4)beta-D-Glcp-(1-->, respectively.

Relevance of peptide uptake systems to the physiology and virulence of Streptococcus agalactiae

Streptococcus agalactiae is a major cause of invasive infections in human newborns. To satisfy its growth requirements, S. agalactiae takes up 9 of the 20 proteinogenic amino acids from the environment. Defined S. agalactiae mutants in one or several of four putative peptide permease systems were constructed and tested for peptide uptake, growth in various media, and expression of virulence traits. Oligopeptide uptake by S. agalactiae was shown to be mediated by the ABC transporter OppA1-F, which possesses two substrate-binding proteins (OppA1 and OppA2) with overlapping substrate specificities. Dipeptides were found to be taken up in parallel by the oligopeptide permease OppA1-F, by the dipeptide ABC transporter DppA-E, and by the dipeptide symporter DpsA. Reverse transcription-PCR analysis revealed a polycistronic organization of the genes oppA1-F and dppA-E and a monocistronic organization of dpsA in S. agalactiae. The results of quantitative real-time PCR revealed a medium-dependent expression of the operons dppA-E and oppA1-F in S. agalactiae. Growth of S. agalactiae in human amniotic fluid was shown to require an intact dpsA gene, indicating an important role of DpsA during the infection of the amniotic cavity by S. agalactiae. Deletion of the oppB gene reduced the adherence of S. agalactiae to epithelial cells by 26%, impaired its adherence to fibrinogen and fibronectin by 42 and 33%, respectively, and caused a 35% reduction in expression of the fbsA gene, which encodes a fibrinogen-binding protein in S. agalactiae. These data indicate that the oligopeptide permease is involved in modulating virulence traits and virulence gene expression in S. agalactiae.

Characterization of a complex restriction-modification system detected in Staphylococcus aureus and Streptococcus agalactiae strains isolated from infections of domestic animals

Characterization of classic type II restriction-modification systems (RMS) (restriction endonucleases and modification methyltransferases) was carried out in isolates of Staphylococcus aureus and Streptococcus agalactiae obtained from clinical material. Among the 100 isolates of S. aureus two different RMS type II were detected. The first was expressed in isolates 32 and 33 (Sau32 I and Sau33 I); the targeting sequence was determined as 5'-GGN CC-3' (Sau96 I isoschizomer). The second was found in isolates no. 90, 93, 96*, and 98 (Sau90 I, Sau93 I, Sau96* I, Sau98 I) and enzymes recognized sequence 5'-CTY RAG-3' (SmlI isoschizomer). Analysis of 40 isolates of S. agalactiae revealed only one RMS; it was detected in two isolates (no. 16 and 23; Sag16 I and Sag23 I). Restriction endonuclease expressed by these isolates cleaved DNA in sequence 5'-CTG CA/G-3' (PstI isoschizomer). In RMS-positive S. aureus and S. agalactiae isolates plasmid DNA capable of replication in Escherichia coli and Bacillus subtilis was also detected and isolated.