Molecular and biological characterization of histidine triad protein in group A streptococci

Four Streptococcus pneumoniae genes, phtA, phtB, phtD, and phtE, as well as the slr gene of group A streptococci (GAS), encode proteins with a histidine triad motif (HxxHxH). Pht proteins function as protective antigens against S. pneumoniae infection. A search of the GAS genome database identified a novel protein, HtpA, possessing five histidine triad motifs. The htpA gene was shown to encode a 92.5-kDa protein located downstream of the fbaA and lbp genes, while Western blot analyses revealed that HtpA protein was expressed on the cell surfaces of all group A, B, C, and G streptococcal isolates tested. Immunization of mice with rHtpA induced antigen-specific antibody production and was effective after a single immunization, with antibody titers remaining constant for at least 84days. In addition, HtpA-immunized mice survived after challenge with GAS strains isolated from patients with streptococcal toxic shock syndrome for significantly longer periods than sham-immunized mice. In that experiment, the HtpA-specific antibody was effectively induced by a single immunization and the specific antibody titer remained constant for at least 84days. These results indicate that the novel histidine triad protein HtpA is a candidate vaccine for GAS infection.     

Phthalate catabolic gene cluster is linked to the angular dioxygenase gene in <Emphasis Type="Italic">Terrabacter</Emphasis> sp. strain DBF63

Phthalate is a metabolic intermediate of the pathway of fluorene (FN) degradation via angular dioxygenation. A gene cluster responsible for the conversion of phthalate to protocatechuate was cloned from the dibenzofuran (DF)- and FN-degrading bacterium Terrabacter sp. strain DBF63 and sequenced. The genes encoding seven catabolic enzymes, oxygenase large subunit of phthalate 3,4-dioxygenase (phtA1), oxygenase small subunit of phthalate 3,4-dioxygenase (phtA2), cis-3,4-dihydroxy-3,4-dihydrophthalate dehydrogenase (phtB), [3Fe-4S] or [4Fe-4S] type of ferredoxin (phtA3), ferredoxin reductase (phtA4), 3,4-dihydroxyphthalate decarboxylase (phtC) and putative regulatory protein (phtR), were found in the upstream region of the angular dioxygenase gene (dbfA1A2), encoded in this order. Escherichia coli carrying phtA1A2BA3A4 genes converted phthalate to 3,4-dihydroxyphthalate, and the 3,4-dihydroxyphthalate decarboxylase activity by E. coli cells carrying phtC was finally detected with the introduction of a Shine-Dalgarno sequence in the upstream region of its initiation codon. Homology analysis on the upstream region of the pht gene cluster revealed that there was an insertion sequence (IS) (ISTesp2; ORF14 and its flanking region), part of which was almost 100% identical to the orf1 and its flanking region adjacent to the extradiol dioxygenase gene ( bphC1) involved in the DF degradation of Terrabacter sp. strain DPO360 [Schmid et al. (1997) J Bacteriol 179:53-62]. This suggests that ISTesp2 plays a role in the metabolism of aromatic compounds in Terrabacter sp. strains DBF63 and DPO360.     

Genetic organization of a cluster of genes involved in the production of phaseolotoxin, a toxin produced by Pseudomonas syringae pv. phaseolicola.

Phaseolotoxin [N delta(N'-sulfo-diaminophosphinyl)-ornithyl-alanyl- homoarginine] produced by Pseudomonas syringae pv. phaseolicola, the bean halo blight pathogen, is a potent inhibitor of ornithine carbamoyltransferase (OCT). Inhibition of OCT in infected plants leads to chlorosis and growth inhibition. A genomic cosmid clone, pHK120, containing a 25-kb fragment of DNA from a wild-type strain of P. syringae pv. phaseolicola restores toxin production in Tox- mutants. Tn5 mutagenesis of pHK120 and marker exchange of pHK120::Tn5 plasmids in the wild-type strain resulted in the isolation of 39 chromosomal mutants that harbor Tn5 insertions at known positions. Toxin bioassays revealed that 28 of the mutants, with Tn5 insertions distributed throughout the insert of pHK120, were Tox-, indicating that a functional locus for toxin production in each mutant was inactivated. Complementation analysis was done by testing for toxin production strains that carried a genomic Tn5 at one location and a plasmid-borne Tn5 at another location (pair complementation). Pair complementation analysis of nine marker exchange mutants and a random genomic Tn5 mutant revealed that there are a minimum of eight toxin loci (phtA through phtH) in pHK120. Mutants carrying Tn5 insertions in the phtA, phtD, and phtF loci were complemented by deletion subclones containing fragments from pHK120; mutants carrying Tn5 insertions in the phtC locus were partially complemented by a subclone, and mutants carrying Tn5 insertions in the phtB, phtE, phtG, and phtH loci were not complemented by any of the available subclones. A comparison of the insert from pHK120 with that from pRCP17, a clone reported previously (R. C. Peet, P. B. Lindgren, D. K. Wills, and N. J. Panopoulos, J. Bacteriol. 166:1096-1105, 1986) by another laboratory to contain some of the phaseolotoxin genes and the phaseolotoxin-resistant OCT gene, revealed that the inserts in these two cosmids overlap but differ in important respects.     

The Metalloregulatory Zinc Site in Streptococcus pneumoniae AdcR, a Zinc-activated MarR Family Repressor

Streptococcus pneumoniae D39 AdcR (adhesin competence repressor) is the first metal-sensing member of the MarR (multiple antibiotic resistance repressor) family to be characterized. Expression profiling with a ΔadcR strain grown in liquid culture (brain-heart infusion) under microaerobic conditions revealed upregulation of 13 genes, including adcR and adcCBA, encoding a high-affinity ABC uptake system for zinc, and genes encoding cell-surface zinc-binding pneumococcal histidine triad (Pht) proteins and AdcAII (Lmb, laminin binding). The ΔadcR, H108Q and H112Q adcR mutant allelic strains grown in 0.2 mM Zn(II) exhibit a slow-growth phenotype and an approximately twofold increase in cell-associated Zn(II). Apo- and Zn(II)-bound AdcR are homodimers in solution and binding to a 28-mer DNA containing an adc operator is strongly stimulated by Zn(II) with K_DNA-Zn = 2.4 × 10⁸ M^- 1 (pH 6.0, 0.2 M NaCl, 25 °C). AdcR binds two Zn(II) per dimer, with stepwise Zn(II) affinities K_Zn1 and K_Zn2 of ≥ 10⁹ M^- 1 at pH 6.0 and ≥ 10¹² M^- 1 at pH 8.0, and one to three lower affinity Zn(II) depending on the pH. X-ray absorption spectroscopy of the high-affinity site reveals a pentacoordinate N/O complex and no cysteine coordination, the latter finding corroborated by wild type-like functional properties of C30A AdcR. Alanine substitution of conserved residues His42 in the DNA-binding domain, and His108 and His112 in the C-terminal regulatory domain, abolish high-affinity Zn(II) binding and greatly reduce Zn(II)-activated binding to DNA. NMR studies reveal that these mutants adopt the same folded conformation as dimeric wild type apo-AdcR, but fail to conformationally switch upon Zn(II) binding. These studies implicate His42, His108 and H112 as metalloregulatory zinc ligands in S. pneumoniae AdcR.     

ZEN1 is a key enzyme in the degradation of nuclear DNA during programmed cell death of tracheary elements

Tracheary elements (TEs) have a unique cell death program in which the rapid collapse of the vacuole triggers the beginning of nuclear degradation. Although various nucleases are known to function in nuclear DNA degradation in animal apoptosis, it is unclear what hydrolase is involved in nuclear degradation in plants. In this study, we demonstrated that an S1-type nuclease, Zinnia endonuclease 1 (ZEN1), functions directly in nuclear DNA degradation during programmed cell death (PCD) of TEs. In-gel DNase assay demonstrated the presence of a 24-kD Ca(2+)/Mg(2+)-dependent nuclease and a 40-kD Zn(2+)-dependent nuclease as well as ZEN1 in 60-h-cultured cells that included differentiating TEs. Such cell extracts possessed the ability to degrade the nuclear DNA isolated from Zinnia elegans cells in the presence of Zn(2+), and its activity was suppressed by an anti-ZEN1 antibody, indicating that ZEN1 is a central DNase responsible for nuclear DNA degradation. The introduction of the antisense ZEN1 gene into Zinnia cells cultured for 40 h specifically suppressed the degradation of nuclear DNA in TEs undergoing PCD but did not affect vacuole collapse. Based on these results, a common mechanism between animal and plant PCD is discussed.     

Virulence of Streptococcus pneumoniae strains belonging to different serovars

The study of the virulence of 352 S. pneumoniae strains isolated from patients with inflammatory lung diseases revealed that their virulence depended, to a certain extent, on the state of the polysaccharide capsule of streptococci, as among 299 typed cultures 38.1% were virulent, while out of 53 nontypable strains of these bacteria only 8 strains (15.1%) proved to be highly pathogenic for white mice and all S. pneumoniae R-forms proved to be avirulent. All 11 S. pneumoniae strains under study belonging to serovars 1 and 2 and 87% of the cultures belonging to serovar 3, isolated from patients with inflammatory lung diseases in Leningrad, were highly virulent. The characteristic feature of S. pneumoniae cultures of other serotypes was their wide spectrum of pathogenicity. S. pneumoniae cultures isolated from the spinal fluid of patients with pneumococcal meningitis also differed in their pathogenicity levels but strains highly pathogenic for mice prevailed.     

Latent LytM at 1.3A resolution

LytM, an autolysin from Staphylococcus aureus, is a Zn(2+)-dependent glycyl-glycine endopeptidase with a characteristic HxH motif that belongs to the lysostaphin-type (MEROPS M23/37) of metallopeptidases. Here, we present the 1.3A crystal structure of LytM, the first structure of a lysostaphin-type peptidase. In the LytM structure, the Zn(2+) is tetrahedrally coordinated by the side-chains of N117, H210, D214 and H293, the second histidine of the HxH motif. Although close to the active-site, H291, the first histidine of the HxH motif, is not directly involved in Zn(2+)-coordination, and there is no water molecule in the coordination sphere of the Zn(2+), suggesting that the crystal structure shows a latent form of the enzyme. Although LytM has not previously been considered as a proenzyme, we show that a truncated version of LytM that lacks the N-terminal part with the poorly conserved Zn(2+) ligand N117 has much higher specific activity than full-length enzyme. This observation is consistent with the known removal of profragments in other lysostaphin-type proteins and with a prior observation of an active LytM degradation fragment in S.aureus supernatant. The "asparagine switch" in LytM is analogous to the "cysteine switch" in pro-matrix metalloproteases.     

Characterization and hetereologous expression of cDNAs encoding two novel closely related Ca(2+)-binding proteins in Dictyostelium discoideum

During a yeast two hybrid screen of a Dictyostelium cDNA library using the Ca(2+)-binding protein CBP1 as bait, we isolated a full-length cDNA encoding a novel Ca(2+)-binding protein (termed CBP4a). The protein is composed of 162 amino acids and contains four consensus EF-hands. PCR amplification of Dictyostelium genomic DNA using primers specific for the cDNA sequence resulted in the isolation of a gene encoding a different Ca(2+)-binding protein of 162 amino acids (designated CBP4b) with 90% amino acid sequence identity to CBP4a. Southern blot analysis confirmed the presence of two closely related genes in the Dictyostelium genome. CBP4a and CBP4b mRNAs are expressed at the same stages of development as CBP1 mRNA. In addition, both novel proteins bind (45)Ca(2+) and interact with CBP1 in vitro in a Ca(2+)-dependent manner.     

Quantitative analysis of Streptococcus pneumoniae TIGR4 response to in vitro iron restriction by 2-D LC ESI MS/MS

Understanding the growth of bacterial pathogens in a micronutrient restricted host environment can identify potential virulence proteins that help overcome this nutritional barrier to productive infection. In this study, we investigated the pneumococcal protein expression response to iron limitation using an in vitro model. We identified S. pneumoniae TIGR4 proteins by 2-D LC ESI MS/MS and determined significant changes in protein expression in response to iron restriction using computer-intensive random resampling methods. Differential protein expression was studied in the context of a S. pneumoniae TIGR4 protein interaction network using Pathway Studio. Our analysis showed that pneumococcal iron restriction response was marked by increased expression of known virulence factors like PsaA. It involved changes in the expression of stress response, and phase variation and biofilm formation proteins. The net effect of changes in all these biological processes could increase the virulence of S. pneumoniae TIGR4 during in vivo infection.     

Ca(2+)-dependent association of S100A6 (Calcyclin) with the plasma membrane and the nuclear envelope.

Expression of S100A6 (Calcyclin), a member of the S100 family and of Zn(2+)-binding proteins is elevated in a number of malignant tumors. In vitro the protein associates with several actin-binding proteins and annexins in a Ca(2+)-dependent manner. We have now studied the subcellular localization of S100A6 using a new, specific monoclonal antibody. Immunofluorescence microscopy of unfixed, ultrathin, frozen sections demonstrated a dual localization of S100A6 at the nuclear envelope and the plasma membrane of porcine smooth muscle only in the presence of Ca(2+). The same localization was found by immunofluorescence and immunogold electron microscopy as well as by confocal laser scanning microscopy with cultured, fixed, human CaKi-2 and porcine ST interphase cells. Upon cell division, however, S100A6 was found exclusively in the cytoplasm. Cell fractionation studies showed that S100A6 was present in the microsomal fraction in the presence of Ca(2+) and was released from this fraction by the addition of EGTA/EDTA but not by Triton X-100. The data demonstrate that S100A6 is localized both at the plasma membrane and the nuclear envelope in vivo and suggest a Ca(2+)-dependent interaction with annexins or other components of the nuclear envelope.     

Human surfactant protein D (SP-D) binds Mycoplasma pneumoniae by high affinity interactions with lipids

Increasing evidence now identifies surfactant protein D (SP-D) as an important element of the innate immune system of the lung. In this study, we examined the interactions of rat and human SP-D with the human pathogen, Mycoplasma pneumoniae. Rat and human SP-D bound the organism with high affinity in a reaction that required Ca(2+) and was inhibited by EGTA. Membranes derived from the organism bound the proteins in a similar manner, except the rat SP-D also exhibited a significant level of Ca(2+)-independent binding. Pretreatment of membranes with proteases did not alter the Ca(2+)-dependent SP-D binding of membranes by either protein. Mannose, glucose, maltose, and inositol, at millimolar concentrations, competed for human SP-D binding to the bacterial membrane. Lipids extracted from membranes and separated by two-dimensional thin layer chromatography bound human SP-D with high affinity in a Ca(2+)-dependent reaction. A tandem mutant of SP-D with E321Q and N323D substitutions, failed to bind M. pneumoniae lipids, directly implicating the carbohydrate recognition domain in the interaction. The interaction of rat and human SP-D with M. pneumoniae was unaffected by the presence of surfactant lipids and the hydrophobic surfactant proteins. These findings demonstrate that M. pneumoniae is likely to be recognized by SP-D in the alveolar environment and that primary determinants recognized on the organism are lipid components of the cell membrane.