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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Shiga toxin is a protein toxin produced by Shigella dysenteriae type I strains. In this report we present a procedure for the separation of functionally intact toxin A and B chains and for their reconstitution to form biologically active molecules. In agreement with the findings of others, the isolated A chain was shown to be a potent in vitro inhibitor of eukaryotic protein synthesis. The isolated B chain bound to HeLa cells and competitively inhibited the binding and cytotoxic activity of holotoxin. These findings show that the functional role of the B chain is to recognize cell surface functional receptors. By labelling the B subunit alone, prior to renaturation of holotoxin, the polypeptide chains were shown to associate noncovalently with a stoichiometry of one A chain and five B chains.
Mol Microbiol 1989 Sep
PMID:Isolation and characterization of functional Shiga toxin subunits and renatured holotoxin. 267 6

Iron limitation, a condition encountered within mammalian hosts, induces the synthesis of a number of proteins in pathogenic Shigella species. These include several outer membrane proteins, Shiga toxin, and proteins involved in the biosynthesis and transport of high-affinity iron-binding compounds or siderophores. Although siderophores have been shown to play a major role in the virulence of some bacterial pathogens, these compounds do not appear to be essential for the virulence of Shigella species. Unlike those pathogens which are restricted to the extracellular compartments of the host, the Shigella species invade and multiply within host cells. Alternative iron-acquisition systems, such as the ability to utilize haem-iron, permit growth of the intracellular bacteria. Virulent shigellae also possess a cell-surface haem-binding protein, and synthesis of this protein correlates with infectivity and virulence. This protein does not appear to be involved in iron acquisition. Rather, it may allow the bacteria to coat themselves with haem compounds, thus enhancing their ability to interact with target host cells.
Mol Microbiol 1989 Sep
PMID:Iron and virulence in Shigella. 267 8

We recently reported the development and assessment of a technique for the detection of Shiga-like toxin-producing Escherichia coli (SLTEC) using the polymerase chain reaction (PCR) and a digoxigenin-11-dUTP-labelled DNA probe. This technique has now been adapted for the direct identification of SLTEC in ground beef. Ground beef homogenates were diluted 1000-fold to reduce the concentration of components which inhibit the thermostable polymerase. Assessment of four different ground beef samples using the PCR detection technique revealed that fat content was a major inhibitory component. As few as 30 SLTEC ml-1 of a ground beef homogenate were detected using the PCR technique, although it was necessary to enrich six of the samples for positive detection. These findings indicate that the PCR detection technique is suitable for the identification of SLTEC directly from contaminated ground beef without isolation of the bacterium or purification of its DNA.
Mol Cell Probes 1995 Aug
PMID:Direct detection of Shiga-like toxin-producing Escherichia coli in ground beef using the polymerase chain reaction. 747 22

Escherichia coli Shiga-like toxin I is a type II ribosome-inactivating protein composed of an A subunit with RNA-specific N-glycosidase activity, non-covalently associated with a pentamer of B subunits possessing affinity for galabiose-containing glycolipids. The A subunit contains a single intrachain disulphide bond encompassing a hydrophilic sequence containing two trypsin-sensitive arginine residues. By analogy with other bacterial toxins it has been proposed that proteolytic nicking, deemed essential for a cytotoxic effect, occurs within this disulphide-bonded loop to generate the A1 and A2 fragments. Reduced A1 is then believed to translocate an internal membrane to inactivate protein synthesis in the cytosol. In this report, the disulphide-loop arginines of the SLT I A subunit were mutated to block the specific proteolysis presumed to occur. However, the mutant generated remained an effective toxin having similar catalytic activity to wild-type toxin and only a marginally reduced cytotoxicity towards cultured cells. We conclude that the disulphide-loop arginine residues are not the unique and essential processing sites previously assumed, but that processing may occur at alternative accessible sites to compensate for loss of target sites within the loop.
Mol Microbiol 1993 Oct
PMID:Proteolytic cleavage at arginine residues within the hydrophilic disulphide loop of the Escherichia coli Shiga-like toxin I A subunit is not essential for cytotoxicity. 796 13

Shiga-like toxin I (SLT-I), the potent cytotoxin produced by certain pathogenic strains of Escherichia coli, is a member of a burgeoning family of ribosome-in-activating proteins (RIPs), which share common structural and mechanistic features. The prototype of the group is the plant toxin ricin. Recently we proposed a structural model for the Slt-IA active site, based in part on the known geometry of the enzymatic subunit of the ricin toxin. The model places three aromatic residues within the putative Slt-IA active site cleft: tyrosine 77, tyrosine 114, and tryptophan 203. Here we present biochemical and biophysical data regarding, the phenotypes of conservative point mutants of Slt-IA in which tyrosine 114 is altered. We used oligonucleotide-directed mutagenesis to replace tyrosine 114 with either phenylalanine (Y114F) or serine (Y114S). Periplasmic extracts of E. coli containing wild-type or mutant Slt-IA were tested for their ability to inhibit protein synthesis in vitro. Relative to wild-type, the activity of mutant Y114F was attenuated about 30-fold, while the mutant Y114S was attenuated about 500 to 1000-fold. In order to address the possibility that differential activation of the mutants rather than local effects at the active site might account for their diminished activity, we engineered the same mutations into a truncated slt-IA cassette that directs expression of a product corresponding to the activated A1 form of Slt-IA (wild-type-delta). The same general relationships held: relative to wild type-delta, Y114F-delta was attenuated about 7-fold, and Y114S-delta about 300-fold.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Gen Genet 1993 Nov
PMID:The role of tyrosine-114 in the enzymatic activity of the Shiga-like toxin I A-chain. 824 1

Isolates of Escherichia coli serotype O157:H7 were identified by an oligonucleotide probe, PF-27, containing a unique base substitution in the allele of the uid A gene. Colony hybridization analysis of 239 bacteria, including E. coli, Shiga-like toxin-producing serogroups of pathogenic E. coli and other enteric isolates showed that the probe reacted only with isolates of serotype O157:H7. Results of genetic analyses suggest that the base substitution in the allele does not contribute to the absence of uid A gene expression in O157:H7.
Mol Cell Probes 1993 Apr
PMID:Identification of Escherichia coli serotype O157:H7 by DNA probe specific for an allele of uid A gene. 832 Dec 53

Recombinant plasmids providing the synthesis of chimeric proteins consisting of amino acid sequences of human interleukin-2 (IL-2) and Shiga toxin cytotoxic A-subunit (ILA and AIL chimeric toxins) were constructed. The ILA and AIL chimeric toxins were shown to inhibit protein synthesis in the rabbit reticulocytes cell-free system. These chimeric toxins displayed two opposite activities of the constituent parts of their molecules on T-lymphocytes from the peripheral blood of healthy volunteers. Hybrid protein AIL (approximately 10(-6) g/ml) has caused the most significant depression of T-lymphoblast proliferation.
Mol Biol (Mosk)
PMID:[Preparation of hybrid proteins consisting of human interleukin-2 and the cytotoxic A-subunit of Shigella toxin]. 836 84

The human epidermoid carcinoma cell line A431 becomes highly sensitive to Shiga toxin upon treatment with butyric acid. This strong sensitization (> 1000-fold) is accompanied by an increase in the fraction of cell-associated toxin transported to the Golgi apparatus and to the endoplasmic reticulum (ER). Furthermore, our previous work showed that the length of the fatty acyl chain of Gb3, the Shiga toxin receptor, also was changed (longer fatty acids). We have not investigated the importance of this change by testing whether glycolipid synthesis is required for the changed intracellular sorting and the toxin sensitivity. We demonstrate here that inhibition of glycosphingolipid synthesis by inhibition of N-acyltransferase with fumonisin B1, by inhibition of glucosylceramide synthetase by PDMP or PPMP, or by inhibition of serine palmitoyl transferase by beta-fluoroalanine, inhibited the butyric acid-induced change in sensitivity and the increase in the fraction of cell-associated Shiga toxin transported to the Golgi apparatus and the ER. The block in butyric acid-induced sensitization caused by beta-fluoroalanine could be abolished by simultaneous addition of sphinganine or sphingosine. Thus, the data suggest that the fatty acyl chain length of glycosphingolipids is important for intracellular sorting and translocation of Shiga toxin to the cytosol.
Mol Biol Cell 1996 Sep
PMID:Importance of glycolipid synthesis for butyric acid-induced sensitization to shiga toxin and intracellular sorting of toxin in A431 cells. 888 34

The gene for a novel, high molecular weight protein secreted by Shiga toxin-producing Escherichia coli (STEC) has been cloned, sequenced and characterized with respect to its activity. This gene, designated pssA, is localized on the large plasmid that also harbours the STEC haemolysin operon. Sequencing of a region comprising 10630nt revealed that the sequences flanking the pssA gene are composed of several remnants of different insertion elements. The PssA protein is produced as a 142kDa precursor molecule that, after N- and C-terminal processing, is released into the culture supernatant as a mature polypeptide of approximately 104kDa. The primary sequence of PssA is highly related to a family of autonomously transported putative virulence factors from different Gram-negative pathogens, which includes the Tsh protein of an avian-pathogenic E. coli strain, the SepA protein from Shigella flexneri and the EspC protein from enteropathogenic E. coli. A common motif present in all four proteins is reminiscent of the catalytic centre of certain serine proteases. PssA (protease secreted by STEC) indeed shows serine protease activity in a casein-based assay and is moreover cytotoxic for Vero cells. This activity of PssA and probably of other proteins of the Tsh family may be of functional importance during infection of the mucosal cell layer by the bacterial pathogen.
Mol Microbiol 1997 Aug
PMID:Characterization of an exported protease from Shiga toxin-producing Escherichia coli. 937 5

Shiga toxin-producing Escherichia coli (STEC), enteropathogenic E. coli (EPEC) and some strains of Hafnia alvei are capable of inducing attaching and effacing (A/E) lesions, characterized by tight apposition of the bacteria to the eukaryotic membrane and formation of actin-based pedestals. In this study, we report on the identification of EspE, a novel secreted 80 kDa protein of A/E bacteria. During infection, EspE is delivered into the cytoplasm of the infected host cell, where it is detected as a higher-molecular-weight form of 90 kDa. We present evidence that translocated EspE becomes tyrosine phosphorylated and that this modified form of EspE may be identical to Hp90, the putative receptor of EPEC intimin. Bacteria of the classic enterohaemorrhagic E. coli (EHEC) serotype O157:H7 fail to induce a tyrosine phosphorylation of EspE and differ in this respect from other A/E bacteria. Translocated EspE, whether tyrosine phosphorylated or not, becomes incorporated into the bacteria-induced cytoskeletal structures, where it normally colocalizes with filamentous actin. EPEC are also able to induce 'pseudopods', elongated pedestals that have recently been implicated in a novel kind of actin-based motility. EspE is enriched at the tip of these structures, suggesting its involvement in the process of actin dynamics, which is triggered during the attaching and effacing process.
Mol Microbiol 1998 May
PMID:EspE, a novel secreted protein of attaching and effacing bacteria, is directly translocated into infected host cells, where it appears as a tyrosine-phosphorylated 90 kDa protein. 963 51


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