Allen, Stuart C. H., Moore, Katherine A. H., Marsden, Catherine J., Fülöp, Vilmos, Moffat, Kevin G., Lord, Mike, Ladds, Graham and Roberts, L. M. (Lynne M.) (2007) The isolation and characterisation of temperature-dependent Ricin A chain molecules in Saccharomyces cerevisiae. FEBS Journal, Vol.274 (No.21). pp. 5586-5599. doi:10.1111/j.1742-4658.2007.06080.x ISSN 1742-464x.

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Abstract

Ricin is a heterodimeric plant protein that is potently toxic to mammalian cells. Toxicity
results from the catalytic depurination of eukaryotic ribosomes by ricin A chain (RTA)
that follows toxin endocytosis to, and translocation across, the endoplasmic reticulum
(ER) membrane. To ultimately identify proteins required for these later steps in the entry
process, it will be useful to express the catalytic subunit within the ER of yeast cells in a
manner that initially permits cell growth. A subsequent switch in conditions to provoke
innate toxin action would permit only those strains containing defects in genes normally
essential for toxin retro-translocation, refolding or degradation to survive. As a route to
such a screen, several RTA mutants with reduced catalytic activity have previously been
isolated. Here we report the use of Saccharomyces cerevisiae to isolate temperaturedependent
mutants of endoplasmic reticulum-targeted RTA. Two such toxin mutants
with opposing phenotypes were isolated. One mutant RTA (RTAF108L/L151P) allowed the
yeast cells that express it to grow at 37°C while the same cells did not grow at 23ºC. Both
mutations were required for temperature-dependent growth. The second toxin mutant
(RTAE177D) allowed cells to grow at 23°C but not at 37°C. Interestingly, RTAE177D has
been previously reported to have reduced catalytic activity, but this is the first
demonstration of a temperature-sensitive phenotype. To provide a more detailed
characterisation of these mutants we have investigated their N-glycosylation, stability,
catalytic activity and, where appropriate, a three dimensional structure. The potential
utility of these mutants is discussed.

Item Type:	Journal Article
Subjects:	Q Science > QK Botany Q Science > QD Chemistry R Medicine > RS Pharmacy and materia medica
Divisions:	Faculty of Science, Engineering and Medicine > Medicine > Warwick Medical School
Library of Congress Subject Headings (LCSH):	Ricinus, Toxins
Journal or Publication Title:	FEBS Journal
Publisher:	Blackwell
ISSN:	1742-464x
Official Date:	4 October 2007
Dates:	Date Event 4 October 2007 Published
Volume:	Vol.274
Number:	No.21
Page Range:	pp. 5586-5599
DOI:	10.1111/j.1742-4658.2007.06080.x
Status:	Peer Reviewed
Description:	Version accepted by publisher (post-print, after peer review, before copy-editing).

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