Lind: Ist Moral lehrbar? Berlin: Logos Verlag 2000. [Rezension]

Rezension von: Lind, Georg.: Ist Moral lehrbar? Berlin: Logos Verlag 2000, 320 S

Yeast Killer Toxin K28: Biology and Unique Strategy of Host Cell Intoxication and Killing

The initial discovery of killer toxin-secreting brewery strains of Saccharomyces cerevisiae (S. cerevisiae) in the mid-sixties of the last century marked the beginning of intensive research in the yeast virology field. So far, four different S. cerevisiae killer toxins (K28, K1, K2, and Klus), encoded by cytoplasmic inherited double-stranded RNA viruses (dsRNA) of the Totiviridae family, have been identified. Among these, K28 represents the unique example of a yeast viral killer toxin that enters a sensitive cell by receptor-mediated endocytosis to reach its intracellular target(s). This review summarizes and discusses the most recent advances and current knowledge on yeast killer toxin K28, with special emphasis on its endocytosis and intracellular trafficking, pointing towards future directions and open questions in this still timely and fascinating field of killer yeast research

Adapting Yeast as Model to Study Ricin Toxin A Uptake and Trafficking

The plant A/B toxin ricin represents a heterodimeric glycoprotein belonging to the family of ribosome inactivating proteins, RIPs. Its toxicity towards eukaryotic cells results from the depurination of 28S rRNA due to the N-glycosidic activity of ricin toxin A chain, RTA. Since the extention of RTA by a mammalian-specific endoplasmic reticulum (ER) retention signal (KDEL) significantly increases RTA in vivo toxicity against mammalian cells, we here analyzed the phenotypic effect of RTA carrying the yeast-specific ER retention motif HDEL. Interestingly, such a toxin (RTAHDEL) showed a similar cytotoxic effect on yeast as a corresponding RTAKDEL variant on HeLa cells. Furthermore, we established a powerful yeast bioassay for RTA in vivo uptake and trafficking which is based on the measurement of dissolved oxygen in toxin-treated spheroplast cultures of S. cerevisiae. We show that yeast spheroplasts are highly sensitive against external applied RTA and further demonstrate that its toxicity is greatly enhanced by replacing the C-terminal KDEL motif by HDEL. Based on the RTA resistant phenotype seen in yeast knock-out mutants defective in early steps of endocytosis (∆end3) and/or in RTA depurination activity on 28S rRNA (∆rpl12B) we feel that the yeast-based bioassay described in this study is a powerful tool to dissect intracellular A/B toxin transport from the plasma membrane through the endosomal compartment to the ER

Correction: Becker, B. et al. Yeast Killer Toxin K28: Biology and Unique Strategy of Host Cell Intoxication and Killing

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Expression of K1 Toxin Derivatives in Saccharomyces cerevisiae Mimics Treatment with Exogenous Toxin and Provides a Useful Tool for Elucidating K1 Mechanisms of Action and Immunity

Killer toxin K1 is a heterodimeric protein toxin secreted by Saccharomyces cerevisiae strains infected with the M1 double-stranded RNA ‘killer’ virus. After binding to a primary receptor at the level of the cell wall, K1 interacts with its secondary plasma membrane receptor Kre1p, eventually leading to an ionophoric disruption of membrane function. Although it has been under investigation for decades, neither the particular mechanisms leading to toxicity nor those leading to immunity have been elucidated. In this study, we constructed derivatives of the K1α subunit and expressed them in sensitive yeast cells. We show that these derivatives are able to mimic the action of externally applied K1 toxin in terms of growth inhibition and pore formation within the membrane, leading to a suicidal phenotype that could be abolished by co-expression of the toxin precursor, confirming a mechanistic similarity of external and internal toxin action. The derivatives were successfully used to investigate a null mutant completely resistant to externally applied toxin. They provide a valuable tool for the identification of so far unknown gene products involved in K1 toxin action and/or immunity

Yeast Reporter Assay to Identify Cellular Components of Ricin Toxin A Chain Trafficking

RTA, the catalytic A-subunit of the ribosome inactivating A/B toxin ricin, inhibits eukaryotic protein biosynthesis by depurination of 28S rRNA. Although cell surface binding of ricin holotoxin is mainly mediated through its B-subunit (RTB), sole application of RTA is also toxic, albeit to a significantly lower extent, suggesting alternative pathways for toxin uptake and transport. Since ricin toxin trafficking in mammalian cells is still not fully understood, we developed a GFP-based reporter assay in yeast that allows rapid identification of cellular components required for RTA uptake and subsequent transport through a target cell. We hereby show that Ypt6p, Sft2p and GARP-complex components play an important role in RTA transport, while neither the retromer complex nor COPIB vesicles are part of the transport machinery. Analyses of yeast knock-out mutants with chromosomal deletion in genes whose products regulate ADP-ribosylation factor GTPases (Arf-GTPases) and/or retrograde Golgi-to-ER (endoplasmic reticulum) transport identified Sso1p, Snc1p, Rer1p, Sec22p, Erv46p, Gea1p and Glo3p as novel components in RTA transport, suggesting the developed reporter assay as a powerful tool to dissect the multistep processes of host cell intoxication in yeast

Exploiting the Yeast L-A Viral Capsid for the In Vivo Assembly of Chimeric VLPs as Platform in Vaccine Development and Foreign Protein Expression

A novel expression system based on engineered variants of the yeast (Saccharomyces cerevisiae) dsRNA virus L-A was developed allowing the in vivo assembly of chimeric virus-like particles (VLPs) as a unique platform for a wide range of applications. We show that polypeptides fused to the viral capsid protein Gag self-assemble into isometric VLP chimeras carrying their cargo inside the capsid, thereby not only effectively preventing proteolytic degradation in the host cell cytosol, but also allowing the expression of a per se cytotoxic protein. Carboxyterminal extension of Gag by T cell epitopes from human cytomegalovirus pp65 resulted in the formation of hybrid VLPs that strongly activated antigen-specific CD8(+) memory T cells ex vivo. Besides being a carrier for polypeptides inducing antigen-specific immune responses in vivo, VLP chimeras were also shown to be effective in the expression and purification of (i) a heterologous model protein (GFP), (ii) a per se toxic protein (K28 α-subunit), and (iii) a particle-associated and fully recyclable biotechnologically relevant enzyme (esterase A). Thus, yeast viral Gag represents a unique platform for the in vivo assembly of chimeric VLPs, equally attractive and useful in vaccine development and recombinant protein production

Implicit and Explicit Attitudes and Interracial Interaction: The Moderating Role of Situationally Available Control Resources

The present research examined whether implicit and explicit racial attitudes predict interracial interaction behavior differently as a function of situationally available control resources. Specifically, we investigated how implicit attitudes (Implicit Association Test) and explicit attitudes (Blatant/Subtle prejudice) were related to interracial interaction behaviors of Italians toward an African interviewer (Study 1) and of Germans toward a Turkish interviewer (Study 2). For half of the interview questions, participants' control resources were reduced via a memory task. Across both studies, the Race IAT was more predictive of behavior when participants were taxed than when untaxed. Conversely, explicit attitudes were somewhat more predictive under full resources. Taken together, our findings suggest that available control resources moderate the predictive validity of implicit and explicit attitudes