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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 63 (1991), S. 529-532 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 37 (2000), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We demonstrate that a virally encoded yeast ‘killer’ toxin is entering its eukaryotic target cell by endocytosis, subsequently travelling the yeast secretory pathway in reverse to exhibit its lethal effect. The K28 killer toxin is a secreted α/β heterodimer that kills sensitive yeasts in a receptor-mediated fashion by blocking DNA synthesis in the nucleus. In vivo processing of the toxin precursor results in a protein whose β-C-terminus carries the endoplasmic reticulum (ER) retention signal HDEL, which, as we show here, is essential for retrograde toxin transport. Yeast end3/4 mutants as well as cells lacking the HDEL receptor (Δerd2) or mutants defective in Golgi-to-ER protein recycling (erd1) are toxin resistant because the toxin can no longer enter and/or retrograde pass the cell. Site-directed mutagenesis further indicated that the toxin's β-HDEL motif ensures retrograde transport, although in a toxin-secreting yeast the β-C-terminus is initially masked by an R residue (β-HDELR) until Kex1p cleavage uncovers the toxin's targeting signal in a late Golgi compartment. Prevention of Kex1p processing results in high-level secretion of a biologically inactive protein incapable of re-entering the secretory pathway. Finally, we present evidence that ER-to-cytosol toxin export is mediated by the Sec61p translocon and requires functional copies of the lumenal ER chaperones Kar2p and Cne1p.
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  • 3
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Zygocin, a monomeric protein toxin secreted by a virus-infected killer strain of the osmotolerant spoilage yeast Zygosaccharomyces bailii, kills a broad spectrum of human and phytopathogenic yeasts and filamentous fungi by disrupting cytoplasmic membrane function. The toxin is encoded by a double-stranded (ds)RNA killer virus (ZbV-M, for Z. bailii virus M) that stably persists within the yeast cell cytosol. In this study, the protein toxin was purified, its N-terminal amino acid sequence was determined, and a full-length cDNA copy of the 2.1 kb viral dsRNA genome was cloned and successfully expressed in a heterologous fungal system. Sequence analysis as well as zygocin expression in Schizosaccharomyces pombe indicated that the toxin is in vivo expressed as a 238-amino-acid preprotoxin precursor (pptox) consisting of a hydrophobic N-terminal secretion signal, followed by a potentially N-glycosylated pro-region and terminating in a classical Kex2p endopeptidase cleavage site that generates the N-terminus of the mature and biologically active protein toxin in a late Golgi compartment. Matrix-assisted laser desorption mass spectrometry further indicated that the secreted toxin is a monomeric 10.4 kDa protein lacking detectable post-translational modifications. Furthermore, we present additional evidence that in contrast with other viral antifungal toxins, zygocin immunity is not mediated by the toxin precursor itself and, therefore, heterologous pptox expression in a zygocin-sensitive host results in a suicidal phenotype. Final sequence comparisons emphasize the conserved pattern of functional elements present in dsRNA killer viruses that naturally infect phylogenetically distant hosts (Saccharomyces cerevisiae and Z. bailii) and reinforce models for the sequence elements that are in vivo required for viral RNA packaging and replication.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 26 (2002), S. 0 
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Since the initial discovery of the yeast killer system almost 40 years ago, intensive studies have substantially strengthened our knowledge in many areas of biology and provided deeper insights into basic aspects of eukaryotic cell biology as well as into virus–host cell interactions and general yeast virology. Analysis of killer toxin structure, synthesis and secretion has fostered understanding of essential cellular mechanisms such as post-translational prepro-protein processing in the secretory pathway. Furthermore, investigation of the receptor-mediated mode of toxin action proved to be an effective means for dissecting the molecular structure and in vivo assembly of yeast and fungal cell walls, providing important insights relevant to combating infections by human pathogenic yeasts. Besides their general importance in understanding eukaryotic cell biology, killer yeasts, killer toxins and killer viruses are also becoming increasingly interesting with respect to possible applications in biomedicine and gene technology. This review will try to address all these aspects.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 38 (2003), S. 0 
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Threatening virus infections constantly illustrate the growing need for novel vaccines that specifically induce efficient T cell-mediated immune responses. In this study, we used a human whole blood assay to determine the activation of antigen-specific human T lymphocytes by a viral antigen of human cytomegalovirus (HCMV). The major HCMV tegument protein pp65, recombinantly expressed in fission yeast (Schizosaccharomyces pombe), specifically activated antigen-specific CD4- and CD8-positive memory T cells in blood of HCMV seropositive donors. Moreover, the immune response against recombinant pp65, in particular that of CD8 class I major histocompatibility complex-restricted cytotoxic T cells, was similar to the response against the intact HCMV. Since fission yeast cells per se did not activate a significant number of human T lymphocytes ex vivo, the system described here might represent a novel approach in vaccine development as well as in the identification of vaccine candidates directly from human whole blood.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 39 (2003), S. 0 
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The human cellular immune response against 14 distantly related yeast species was analyzed by intracellular cytokine staining of lymphocytes after ex vivo stimulation of whole blood. While the CD4 T cell response was marginal, extensive MHC class I-restricted CD8 T cell responses were detected against a number of species including spoiling, environmental and human pathogenic yeasts. The yeast-specific CD8 T cells expressed interferon-γ but lacked expression of CD27 and CCR7, indicating that they were end-differentiated effector memory cells. Mainly intact yeast cells rather than spheroplasts were able to induce cytokine expression in T cells demonstrating that the dominant immunogens were located in the yeast cell wall. Together these data underline the importance of the cellular immune response in protecting humans against yeast and fungal infections. And, from another perspective, recombinant yeast suggests itself as a potential vaccine candidate to efficiently induce antigen-specific CD8 T cell responses.
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  • 7
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The serine protease urokinase-type plasminogen activator (uPA) mediates cancer invasion and metastasis by binding to a cell surface receptor (uPA-R, CD87) on both tumor and stromal cells. In the present study we assessed uPA-R distribution in formalin-fixed, paraffin-embedded breast cancer specimens (n=50) and benign lesions (n=10) by immunohistochemistry employing a newly developed polyclonal chicken antibody to uPA-R (pAb HU277) in parallel with established monoclonal antibody (mAb) 3936 to uPA-R. In addition, uPA-R mRNA synthesis was investigated by in situ hybridization. In all of the sections analyzed, macrophage-like cells reacted with either antibody type. In 22 of the 50 cancer specimens, tumor cells reacted with pAb HU277 in contrast to mAb 3936 which only stained 9 of the 22 positive cases. Nevertheless, in 49 of the 50 cases, uPA-R mRNA was detected in cancer and in stromal cells by in situ hybridization suggesting posttranscriptional regulation of uPA-R expression in breast cancer cells. In 18 of 50 cases, uPA-R mRNA was also visualized in blood vessel lining endothelial cells by in situ hybridization and applying pAb HU277 in 14 of these 18 cases by immunohistochemistry. mAb 3936 did not stain any endothelial cells. pAb HU277 reacted with the breast gland epithelial cells of benign lesions as well, in contrast to mAb 3936 which did not. As for the cancer tissue, in benign lesions, endothelial cells were sporadically stained by pAb HU277. This antibody, but not mAb 3936, also stained myoepithelial cells in intraductal areas of invasive breast carcinoma. The results presented demonstrate the usefulness of pAb HU277 in locating uPA-R in tumor and normal cells with high sensitivity in formalin-fixed, paraffin-embedded breast tissue.
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  • 8
    ISSN: 1432-0983
    Keywords: PCR ; Southern blot ; Gene probe ; Gene bank screening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have developed a protocol to isolate a gene from which only limited (amino-acid) sequence information is available. It involves two PCR amplifications using one constant primer and a set of nested primers and subsequent crosswise Southern hybridization. The amplified DNA giving a signal in both lanes is further processed for use in gene bank screening by applying standard procedures. In this way the structural gene for a thiol protease, BLH1, the homologue of the bleomycin A (a cancerostatic drug) resistance gene of rabbit (and man), was isolated from yeast genomic DNA.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 246 (1995), S. 236-246 
    ISSN: 1617-4623
    Keywords: Yeast ; K28 killer toxin ; cDNA expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The killer toxin K28, secreted by certain killer strains of the yeast Saccharomyces cerevisiae is genetically encoded by a 1.9 kb double-stranded RNA, M-dsRNA (M28), that is present within the cell as a cytoplasmically inherited virus-like particle (VLP). For stable maintenance and replication, M28-VLPs depend on a second dsRNA virus (LA), which has been shown to encode the major capsid protein (cap) and a capsidpolymerase fusion protein (cap-pol) that provides the toxin-coding M-satellites with their transcription and replicase functions. K28 toxin-coding M28-VLPs were isolated, purified and used in vitro for the synthesis of the single-stranded M28 transcript, which was shown to be of plus strand polarity and to bind to oligo(dT)-cellulose, indicating that M28(+)ssRNA contains an internal A-rich tract. Strand separation of the 1.9 kb M28-dsRNA and direct RNA sequencing of its 3′ ends was performed in order to obtain specific DNA oligonucleotides that could be used as primers for cDNA synthesis. The nucleotide sequence of the toxin-coding M28-cDNA identified a single open reading frame (ORF) coding for a polypeptide of 345 amino acids, which contained two potential Kex2p/Kex1p processing sites and three potential sites for protein N-glycosylation. The toxin-coding cDNA was cloned and expressed in sensitive non-killer strains under the control of the yeast PGK promoter. Upon transformation, this construct conferred the complete K28 phenotype, demonstrating that both toxin and immunity determinants are contained within the cloned cDNA. In vitro translational analysis of the M28(+)ssRNA in vitro transcript identified the primary gene product of M28 as a K28 preprotoxin of 38 kDa (M-p38).
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Antonie van Leeuwenhoek 58 (1990), S. 277-282 
    ISSN: 1572-9699
    Keywords: Saccharomyces cerevisiae ; killer toxin K28 ; glycoprotein ; O-glycosylation ; β-elimination ; α-toxin antibodies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Killer toxin K28, a 16 kd protein secreted by the wine yeast Saccharomyces cerevisiae strain 28, was reversibly bound by a column of Concanavalin A-Sepharose, confirming its glycoprotein nature. HPLC analysis of acid hydrolyzates of K28 toxin as well as Western-blots of β-eliminated and/or endo H-treated killer toxin preparations probed with polyclonal α-toxin antibodies revealed that the carbohydrate moiety of K28 consists of D-mannose only, which is O-glycosidically linked via Ser/Thr residues to the protein part. The change in gel mobility of K28 after β-elimination was caused by a decrease in molecular mass of about 1,800, corresponding to a carbohydrate moiety of 10 mannose residues per killer toxin molecule.
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