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Cytosolic chaperones influence the fate of a toxin dislocated from the endoplasmic reticulum

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Spooner, Robert A., Harte, Philip J. , Cook, Jonathan P., Pietroni, Paola, Rogon, Christian, Höhfeld, Jörg, Roberts, Lynne M. and Lord, Mike (J. Mike). (2008) Cytosolic chaperones influence the fate of a toxin dislocated from the endoplasmic reticulum. Proceedings of the National Academy of Sciences of the United States of America, Vol.105 (No.45). pp. 17408-17413. ISSN 0027-8424

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Official URL: http://dx.doi.org/10.1073/pnas.0809013105

Abstract

The plant cytotoxin ricin enters target mammalian cells by receptor-mediated endocytosis and undergoes retrograde transport to the endoplasmic reticulum (ER). Here, its catalytic A chain (RTA) is reductively separated from the cell-binding B chain, and free RTA enters the cytosol where it inactivates ribosomes. Cytosolic entry requires unfolding of RTA and dislocation across the ER membrane such that it arrives in the cytosol in a vulnerable, nonnative conformation. Clearly, for such a dislocated toxin to become active, it must avoid degradation and fold to a catalytic conformation. Here, we show that, in vitro, Hsc70 prevents aggregation of heat-treated RTA, and that RTA catalytic activity is recovered after chaperone treatment. A combination of pharmacological inhibition and cochaperone expression reveals that, in vivo, cytosolic RTA is scrutinized sequentially by the Hsc70 and Hsp90 cytosolic chaperone machineries, and that its eventual fate is determined by the balance of activities of cochaperones that regulate Hsc70 and Hsp90 functions. Cytotoxic activity follows Hsc70-mediated escape of RTA from an otherwise destructive pathway facilitated by Hsp90. We demonstrate a role for cytosolic chaperones, proteins typically associated with folding nascent proteins, assembling multimolecular protein complexes and degrading cytosolic and stalled, cotranslocational clients, in a toxin triage, in which both toxin folding and degradation are initiated from chaperone-bound states.

Item Type:	Journal Article
Subjects:	Q Science > QH Natural history > QH301 Biology
Divisions:	Faculty of Science > Life Sciences (2010- ) > Biological Sciences ( -2010)
Library of Congress Subject Headings (LCSH):	Toxins, Endoplasmic reticulum , Endocytosis
Journal or Publication Title:	Proceedings of the National Academy of Sciences of the United States of America
Publisher:	National Academy of Sciences
ISSN:	0027-8424
Date:	6 November 2008
Volume:	Vol.105
Number:	No.45
Page Range:	pp. 17408-17413
Identification Number:	10.1073/pnas.0809013105
Status:	Peer Reviewed
Access rights to Published version:	Open Access
Funder:	Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC), National Institutes of Health (U.S.) (NIH), Wellcome Trust (London, England), Deutsche Forschungsgemeinschaft (DFG)
Grant number:	5U01AI65869-02 (NIH), 080566Z/06/Z (Wellcome), SFB635 (DF).
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URI:	http://wrap.warwick.ac.uk/id/eprint/410