Associated roles of hemolysin and p60 protein for the intracellular growth of Bacillus subtilis

Hemolysin expressing Bacillus subtilis strain (B. subtilis ble/hlA) was used as a carrier for listerial protein p60 to study the impact of this protein on bacterial virulence independent of other gene products of Listeria monocytogenes. Bacillus subtilis ble/hlyA exhibited longer cell chains than B. subtilis ble/hlyA/iap. Recombinant Bacillus strains are able to adhere to the mouse macrophage-like J774 and human epithelial-like Int407 cell lines. The bacterial number of B. subtilis ble/hlyA/iap strain that adhered to the Int407 cell lines was 2.52-fold higher, and its invasion level strain was 2.66-fold higher than that observed for the hemolytic strain. Microscopy analysis of infected monolayers showed that recombinant B. subtilis cells were localized inside the cytoplasm of epithelial cells, near to the nuclei, in cellular compartments with low internal pH. Furthermore, in cells infected with bacteria, the actin structures rapidly changed and accumulation of a fat, wide actin layer around the nucleus zone was observed.     

Transport of hemolysin by Escherichia coli

The hemolytic phenotype in Escherichia coli is determined by four genes. Two (hlyC and hlyA) determine the synthesis of a hemolytically active protein which is transported across the cytoplasmic membrane. The other two genes (hlyBa and hlyBb) encode two proteins which are located in the outer membrane and seem to form a specific transport system for hemolysin across the outer membrane. The primary product of gene hlyA is a protein (protein A) of 106,000 daltons which is nonhemolytic and which is not transported. No signal peptide can be recognized at its N-terminus. In the presence of the hlyC gene product (protein C), the 106,000-dalton protein is processed to the major proteolytic product of 58,000 daltons, which is hemolytically active and is transported across the cytoplasmic membrane. Several other proteolytic fragments of the 106,000-dalton protein are also generated. During the transport of the 58,000-dalton fragment (and possible other proteolytic fragments of hlyA gene product), the C protein remains in the cytoplasm. In the absence of hlyBa and hlyBb the entire hemolytic activity (mainly associated with the 58,000-dalton protein) is located in the periplasm: Studies on the location of hemolysin in hlyBa and hlyBb mutants suggest that the gene product of hlyBa (protein Ba) binds hemolysin and leads it through the outer membrane whereas the gene product of hlyBb (protein Bb) releases hemolysin from the outer membrane. This transport system is specific for E coli hemolysin. Other periplasmic enzymes of E coli and heterologous hemolysin (cereolysin) are not transported.     

Extracellular proteins of Vibrio cholerae: nucleotide sequence of the structural gene (hlyA) for the haemolysin of the haemolytic El Tor strain 017 and characterization of the hlyA mutation in the non-haemolytic classical strain 569B

The EI T or haemolysin, product of hlyA, is exported from Vibrio cholerae as a Mr 80,000 protein which can be subsequently cleaved to give two proteins of Mr 65,000 and 15,000. Nucleotide sequence analysis has demonstrated that hlyA encodes a protein of Mr 82,250 with a potential 18-amino-acid signal sequence. The non-haemolytic classical strain 569B has been shown to have a structural gene defect rather than a defect in secretion. By non-reciprocal recombination it was possible to transfer this defect onto a plasmid and show that a truncated hlyA product of Mr 27,000 is made in Escherichia coli K-12 minicells. Nucleotide sequence analysis demonstrates an 11-base-pair deletion which would result in a Mr 26,940 protein probably loosely associated with the membrane.     

Cloning and functional characterization of the plasmid-encoded hemolysin determinant of Escherichia coli.

We cloned the DNA containing the Escherichia coli hemolysin determinant on a small, high-copy plasmid. We generated plasmids containing fragments of this DNA and used them either alone or in two-plasmid complementation systems to define the limits of the structural genes. This system also allowed us to partially characterize the function of each of the gene products in the production and transport of hemolysin. Taken with previously published data, the present experiments indicate the following. (i) At least three cistrons, hlyC, hlyA, and hlyB (these were previously designated cisC, etc. [Noegel et al., Mol. Gen. Genet. 175:343-350, 1979]), contain the specific genetic information for the hemolytic phenotype, (ii) hlyA encodes a 107,000-kilodalton protein, which seems to be an inactive precursor of hemolysin. (iii) Normal amounts of hemolysin activity inactive precursor of hemolysin. (iii) Normal amounts of hemolysin activity require only the products of hlyA and hlyC. This activity was found in the periplasm; very little hemolysin activity was found in the cytoplasm, suggesting that the hlyC product is required for transport or activation of the hlyA product or both. (iv) Active hemolysin remains in the periplasm in the absence of hlyB function, hence the hlyB product seems to be necessary for the transport of hemolysin to the exterior of the cell. We further show that overproduction of the hlyA product is lethal, probably causing lysis of the cell.     

Homologues of neisserial heme oxygenase in gram-negative bacteria: degradation of heme by the product of the pigA gene of Pseudomonas aeruginosa

The oxidative cleavage of heme to release iron is a mechanism by which some bacterial pathogens can utilize heme as an iron source. The pigA gene of Pseudomonas aeruginosa is shown to encode a heme oxygenase protein, which was identified in the genome sequence by its significant homology (37%) with HemO of Neisseria meningitidis. When the gene encoding the neisserial heme oxygenase, hemO, was replaced with pigA, we demonstrated that pigA could functionally replace hemO and allow for heme utilization by neisseriae. Furthermore, when pigA was disrupted by cassette mutagenesis in P. aeruginosa, heme utilization was defective in iron-poor media supplemented with heme. This defect could be restored both by the addition of exogenous FeSO4, indicating that the mutant did not have a defect in iron metabolism, and by in trans complementation with pigA from a plasmid with an inducible promoter. The PigA protein was purified by ion-exchange chromotography. The UV-visible spectrum of PigA reconstituted with heme showed characteristics previously reported for other bacterial and mammalian heme oxygenases. The heme-PigA complex could be converted to ferric biliverdin in the presence of ascorbate, demonstrating the need for an exogenous reductant. Acidification and high-performance liquid chromatography analysis of the ascorbate reduction products identified a major product of biliverdin IX-beta. This differs from the previously characterized heme oxygenases in which biliverdin IX-alpha is the typical product. We conclude that PigA is a heme oxygenase and may represent a class of these enzymes with novel regiospecificity.     

日本脑炎病毒E蛋白在酵母双杂交系统中的表达及其对报告基因激活作用的检测

用日本脑炎病毒(JEV)E蛋白基因片段构建酵母双杂交诱饵载体,并检测其表达产物对酵母细胞有无毒性作用及对报告基因有无激活作用。用RT—PCR从JEV感染的鼠脑中扩增出JEV E蛋白基因片段,克隆入pUCl9质粒,经测序正确后,再亚克隆入酵母双杂交诱饵载体pGBKT7中。将重组质粒导入酵母菌AHl09,检测其表达产物在酵母细胞中对报告基因有无激活作用。成功获得JEV E蛋白基因片段,表达的E蛋白对酵母菌AHl09无毒性,对报告基因亦无激活作用。为利用酵母双杂交GAL4系统3进行JEV细胞受体蛋白的研究奠定了基础。     

Tropic1808基因的原核表达及其表达产物的生物活性

Tropic180 8基因是新近获得的一个鼠源性的cDNA .Tropic180 8基因开放阅读框架片段通过PCR方法从质粒中扩增后 ,重组入表达载体pET 2 1a中 ,转化大肠杆菌BL2 1(DE3 ) .用IPTG诱导目的蛋白的表达 ,SDS PAGE并凝胶图象分析确定目的蛋白表达水平占细菌总蛋白的 14%以上 .表达蛋白在N端融合有 16个氨基酸 ,将表达蛋白电转移至PVDF膜 .氨基酸序列分析表明 ,其N端第 17～ 2 5位氨基酸序列与Tropic180 8基因编码序列一致 .利用融合部分含T7·Tag ,通过亲和层析纯化表达蛋白 ,经Westernblot检测为目的蛋白 ,加入到无血清培养的新生SD大鼠背根神经节 (DRG)中 ,观察到表达蛋白对DRG具有促进存活和促进突起生长的作用 .     

结核杆菌 D29 噬菌体几丁质酶基因的表达及功能研究

噬菌体一般通过表达内溶素来降解宿主菌细胞壁上的肽聚糖 . 用 PCR 技术从结核杆菌 D29 噬菌体基因组中克隆了 gene10 ,并使其在大肠杆菌中得到了高效表达,蛋白质 C 端带有 6×His. 用镍柱亲和纯化了大肠杆菌表达的 gp10 蛋白可溶性部分 . 活性测定表明, gp10 不但具有几丁质酶活性,还具有溶菌酶活性,是一种双功能的酶 . 耻垢杆菌经 gp10 作用后,其生长受到抑制,扫描电镜观察发现部分耻垢杆菌被降解 . 说明与其他种类噬菌体降解细胞壁的方式不同, D29 噬菌体可能利用 gp10 的溶菌酶活性使结核杆菌细胞壁降解 . 这有助于揭示结核杆菌噬菌体与其宿主的相互作用机制,是关于噬菌体几丁质酶的首次报道 .     

Isolation and characterization of human HSP70 expressed in Escherichia coli

A plasmid containing the human HSP70 gene was used to transfect and express the protein in Escherichia coli. The bacterial product was a fusion protein containing 640 amino acids of HSP70, plus 33 additional NH2 terminal amino acids; 12 from the bacterial expression vector and 21 from a 5' human sequence that is not normally translated. It was partially purified by ion-exchange and ATP-Sepharose affinity column chromatography. The bacterially produced human HSP70 protein was then compared with HSP70 obtained from cultured 293 cells. Both shared the same staphylococcal V8 protease peptide fragment pattern, ATP binding, and a weak ATPase activity (about 10-15 nmol ATP hydrolyzed per milligram protein per minute at 30 degrees C). The bacterially produced human HSP70 protein differed in its V8 protease pattern with an E. coli ATP-binding protein that corresponded in molecular mass to the E. coli dnaK gene product. Mutants in the human HSP70 gene were constructed which significantly reduced a predicted major alpha-helical domain in the HSP70 molecule that has partial homology to an ATP-binding site of several protein kinases. One HSP70 mutant clone contained a deletion of 20% at the NH2 terminus, and expressed a 57-kDa product, while the other was missing the middle 50% of the gene (40-kDa product). Neither protein fragment bound to an ATP affinity column, suggesting that ATP binding to HSP70 may be conformationally affected by a region about 20% internal to the NH2 terminal end of the molecule. Recently, a similar location of the ATP-binding site has been reported by Milarski and Morimoto (27).     

Characterisation of HlyC and mechanism of activation and secretion of haemolysin from E. coli 2001

In this paper the DNA sequence of the cloned hlyC gene from E. coli 2001 is presented. The gene encodes a protein of 20 kDa which is able to activate the 107 kDa polypeptide encoded by hlyA. This gives rise to a haemolytically active protein which differs from the inactive form in stability and by its migration when analysed by polyacrylamide gel electrophoresis under non-denaturing conditions. We also show that the inactive form is secreted in the presence of the transport functions hlyB and hlyD. This result rules out any role for the hlyC gene product in the transport of HlyA across the inner membrane.     

Identification of the teichoic acid phosphorylcholine esterase in Streptococcus pneumoniae

Streptococcus pneumoniae is a major human pathogen and many interactions of this bacterium with its host appear to be mediated, directly or indirectly, by components of the bacterial cell wall, specifically by the phosphorylcholine residues which serve as anchors for surface-located choline-binding proteins and are also recognized by components of the host response, such as the human C-reactive protein, a class of myeloma proteins and PAF receptors. In the present study, we describe the identification of the pneumococcal pce gene encoding for a teichoic acid phosphorylcholine esterase (Pce), an enzymatic activity capable of removing phosphorylcholine residues from the cell wall teichoic acid and lipoteichoic acid. Pce carries an N-terminal signal sequence, contains a C-terminal choline-binding domain with 10 homologous repeating units similar to those found in other pneumococcal surface proteins, and the catalytic (phosphorylcholine esterase) activity is localized on the N-terminal part of the protein. The mature protein was overexpressed in Escherichia coli and purified in a one-step procedure by choline-affinity chromatography and the enzymatic activity was followed using the chromophoric p-nitrophenyl-phosphorylcholine as a model substrate. The product of the enzymatic digestion of 3H-choline-labelled cell walls was shown to be phosphorylcholine. Inactivation of the pce gene in S. pneumoniae strains by insertion-duplication mutagenesis caused a unique change in colony morphology and a striking increase in virulence in the intraperitoneal mouse model. Pce may be a regulatory element involved with the interaction of S. pneumoniae with its human host.     

AH23848 accelerates inducible nitric oxide synthase degradation through attenuation of cAMP signaling in glomerular mesangial cells.

Excessive release of nitric oxide (NO) by mesangial cells contributes to the pathogenesis of glomerulonephritis. Prostaglandin E(2) (PGE(2)) produced at inflammatory sites regulates the release of NO through its downstream signaling. In glomerular mesangial cells (MES-13 cells), PGE(2) modulated NO production mainly through EP4 receptor in a cAMP-dependent manner. Lipopolysaccharide and interferon-gamma (LPS+IFNgamma)-induced NO production, inducible nitric oxide synthase (iNOS) gene and protein expression were greatly inhibited by AH23848, an EP4 antagonist. Further investigation indicated that AH23848 attenuated endogenous cAMP accumulation in MES-13 cells and modulated NO production through declination of iNOS gene expression and acceleration of iNOS protein degradation. AH23848 downregulated the iNOS protein in MES-13 cells through protein kinase A (PKA) since KT5720, a PKA-specific inhibitor, reduced iNOS protein stability. A short exposure of activated MES-13 cells to okadaic acid augmented iNOS activity. AH23848 and KT5720 attenuated serine/threonine phosphorylation of iNOS protein in LPS + IFNgamma-stimulated MES-13 cells. The results of this study led us to speculate that cAMP might regulate iNOS-stimulated NO synthesis through posttranslational mechanisms. Attenuation of cAMP signaling and the phosphorylation status of the iNOS protein may account for the effect of AH23848 in accelerating iNOS protein degradation in MES-13 cells.     

Poly-γ-glutamate depolymerase of Bacillus subtilis: production, simple purification and substrate selectivity

The Bacillus subtilis pgdS gene, which is located at the immediate downstream of the pgs operon for poly-γ-glutamate (PGA) biosynthesis, encodes a PGA depolymerase. The pgdS gene product shows the structural feature of a membrane-associated protein. The mature form of the gene product, identified as a B. subtilis extracellular protein, was produced in Escherichia coli clone cells. Since the mature PGA depolymerase has been modified with the histidine-tag at its C-terminus, it could be simply purified by metal-chelating affinity chromatography. This purified enzyme digested PGAs from B. subtilis ( -glutamate content, 70%) and from Bacillus megaterium (30%) in an endopeptidase-like fashion. In contrast, PGA from Natrialba aegyptiaca, which consists only of -glutamate, was resistant to the enzyme, suggesting that, unlike fungal PGA endo-depolymerases, the bacterial enzyme recognizes the -glutamate unit in PGA.     

High-level expression of the Listeria monocytogenes listeriolysin O in Escherichia coli and preliminary characterization of the purified protein

Listeriolysin O (LLO) is a cholesterol-binding sulfhydryl-activated hemolysin encoded by Listeria monocytogenes hlyA gene. After analyzing the nucleotide coding sequence of this gene from the ATCC 9525 L. monocytogenes strain, we cloned it in a pET vector for expression in Escherichia coli. Thanks to the optimization of the induction protocol, we achieved a high-level LLO synthesis (about 10% of total cell proteins) in hemolytically active form. The expressed hemolysin was then purified to homogeneity, as revealed by SDS-PAGE and Western blot analysis, by a hydroxyapatite adsorption chromatography, followed by an SP Sepharose ion-exchange chromatography. The recombinant protein showed the same properties determined for LLO purified from L. monocytogenes cultures and the characteristics of the sulfhydryl-activated toxins such as inactivation by oxidation and by reaction with cholesterol. By a combination of the pET expression system and the simple purification method, we obtained a significant amount of toxin (4.5 mg/litre cell culture) in a hemolytically active form (1.25 x 10(6)HU/mg protein). This procedure can solve the problem of LLO isolation from L. monocytogenes cultures, which is a difficult task, mainly owing to the low levels of toxin released in the culture media. The recombinant hemolysin, purified in sufficient quantities, could be very useful for structural studies and for diagnostic and pharmaceutical applications.     

The nucleotide sequence of the Escherichia coli K12 dnaJ+ gene. A gene that encodes a heat shock protein

The Escherichia coli dnaJ gene product is required for bacteriophage lambda DNA replication at all temperatures. It is also essential for bacterial viability in at least some conditions, since mutations in it result in temperature-sensitive bacterial growth. We have previously cloned the dnaJ gene and shown that its product migrates as a Mr 37,000 polypeptide under denaturing conditions. Here we present the primary DNA sequence of the dnaJ gene. It codes for a processed basic protein (63 basic and 51 acidic amino acids) composed of 375 amino acids totaling Mr 40,973. The predicted NH2-terminal amino acid sequence, overall amino acid composition, and isoelectric point agree well with those of the purified protein. We present evidence that the rate of expression of the dnaJ protein is increased by heat shock under the control of the htpR (rpoH) gene product.     

Cloning and expression of the yeast plasma membrane ATPase in Escherichia coli

The yeast plasma membrane ATPase gene PMA1 was cloned into Escherichia coli using the high expression tac and T7 promoters. The gene product is toxic to the bacterial cell leading to very low expression levels and arrested growth of the host cell within minutes of induction. The expressed protein is immunologically cross-reactive with the yeast ATPase, comigrates with the original protein in sodium dodecyl sulfate-polyacrylamide gels, and is isolated in the E. coli membrane fraction. The partially purified protein exhibits ATPase activity.     

Leishmania mexicana amazonensis: development of a peptide tag useful for labeling and purifying biotinylated recombinant proteins

A number of peptide tags are available to facilitate the characterization of recombinant proteins. We have tested the bacterial oxaloacetate decarboxylase biotinylation domain for its efficacy in tagging recombinant proteins in vivo in Leishmania. To achieve efficient biotinylation, Leishmania also had to be co-transformed with the gene for bacterial biotin protein ligase (birA gene product). The recombinant chimeric protein could be detected on blots probed with avidin-horseradish peroxidase and purified on immobilized monomeric avidin resins.