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Toxins 2015, 7(1), 49-65;

Ricin Trafficking in Cells

School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
Authors to whom correspondence should be addressed.
Academic Editor: Nilgun E. Tumer
Received: 26 November 2014 / Accepted: 30 December 2014 / Published: 9 January 2015
(This article belongs to the Special Issue Plant Toxins)
Full-Text   |   PDF [806 KB, uploaded 9 January 2015]   |  


The heterodimeric plant toxin ricin binds exposed galactosyls at the cell surface of target mammalian cells, and, following endocytosis, is transported in vesicular carriers to the endoplasmic reticulum (ER). Subsequently, the cell-binding B chain (RTB) and the catalytic A chain (RTA) are separated reductively, RTA embeds in the ER membrane and then retrotranslocates (or dislocates) across this membrane. The protein conducting channels used by RTA are usually regarded as part of the ER-associated protein degradation system (ERAD) that removes misfolded proteins from the ER for destruction by the cytosolic proteasomes. However, unlike ERAD substrates, cytosolic RTA avoids destruction and folds into a catalytic conformation that inactivates its target ribosomes. Protein synthesis ceases, and subsequently the cells die apoptotically. This raises questions about how this protein avoids the pathways that are normally sanctioned for ER-dislocating substrates. In this review we focus on the molecular events that occur with non-tagged ricin and its isolated subunits at the ER–cytosol interface. This focus reveals that intra-membrane interactions of RTA may control its fate, an area that warrants further investigation. View Full-Text
Keywords: ricin; ER-cytosol retrotranslocation; p24 proteins; ERP2; HRD1; proteasome; RPT; chaperone ricin; ER-cytosol retrotranslocation; p24 proteins; ERP2; HRD1; proteasome; RPT; chaperone

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Spooner, R.A.; Lord, J.M. Ricin Trafficking in Cells. Toxins 2015, 7, 49-65.

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