scholarly journals Ricin A Chain Insertion into Endoplasmic Reticulum Membranes Is Triggered by a Temperature Increase to 37 °C

2009 ◽  
Vol 284 (15) ◽  
pp. 10232-10242 ◽  
Author(s):  
Peter U. Mayerhofer ◽  
Jonathan P. Cook ◽  
Judit Wahlman ◽  
Teresa T. J. Pinheiro ◽  
Katherine A. H. Moore ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Temperature Increase ◽  
Ricin A Chain ◽  
A Chain ◽  
Ricin A

Ricin A chain reaches the endoplasmic reticulum after endocytosis

2006 ◽  
Vol 343 (3) ◽  
pp. 857-863 ◽  
Author(s):  
Qiong Liu ◽  
Jinbiao Zhan ◽  
Xinhong Chen ◽  
Shu Zheng
Keyword(s):  
Endoplasmic Reticulum ◽  
Ricin A Chain ◽  
A Chain ◽  
Ricin A

scholarly journals Protein disulphide-isomerase reduces ricin to its A and B chains in the endoplasmic reticulum

2004 ◽  
Vol 383 (2) ◽  
pp. 285-293 ◽  
Author(s):  
Robert A. SPOONER ◽  
Peter D. WATSON ◽  
Catherine J. MARSDEN ◽  
Daniel C. SMITH ◽  
Katherine A. H. MOORE ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Proteolytic Cleavage ◽  
Ricin A Chain ◽  
Protein Disulphide Isomerase ◽  
Biphasic Kinetics ◽  
Early Retention ◽  
A Chain ◽  
Ricin A ◽  
Slow Turnover

Cells expressing ricin B chain within the secretory pathway are significantly more resistant to intoxication by ricin holotoxin but not to other cytotoxins that exploit similar endocytic routes to the cytosol. Furthermore, cells expressing the related B chain of abrin are protected against both incoming abrin and ricin. These phenotypes can be correlated with the abilities of the respective B chains to form disulphide-linked A–B holotoxins, since abrin B chain forms heterodimers with either abrin or ricin A chains, whereas ricin B chain forms heterodimers with ricin A chain only. In the ricin B-expressing cells, this newly made lectin disappears with biphasic kinetics comprising a retention phase followed by slow turnover and disposal after disengagement from calnexin cycle components. Interference with ricin cytotoxicity occurs during the early retention phase when ricin B chain is associated with PDI (protein disulphide-isomerase). The data show that retrotranslocation of incoming toxin is impeded by PDI-catalysed formation of heterodimers between endogenous B and A chains derived from reduced holotoxin, thus proving that reduction of ricin occurs in the endoplasmic reticulum. In contrast with other toxins, ricin does not appear to require either proteolytic cleavage or unfolding for PDI-catalysed reduction.

scholarly journals The Png1–Rad23 complex regulates glycoprotein turnover

2006 ◽  
Vol 172 (2) ◽  
pp. 211-219 ◽  
Author(s):  
Ikjin Kim ◽  
Jungmi Ahn ◽  
Chang Liu ◽  
Kaori Tanabe ◽  
Jennifer Apodaca ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Substrate Specificity ◽  
Protein Degradation ◽  
Binding Proteins ◽  
Degradation Pathways ◽  
Ricin A Chain ◽  
Substrate Degradation ◽  
A Chain ◽  
Specific Degradation ◽  
Ricin A

Misfolded proteins in the endoplasmic reticulum (ER) are destroyed by a pathway termed ER-associated protein degradation (ERAD). Glycans are often removed from glycosylated ERAD substrates in the cytosol before substrate degradation, which maintains the efficiency of the proteasome. Png1, a deglycosylating enzyme, has long been suspected, but not proven, to be crucial in this process. We demonstrate that the efficient degradation of glycosylated ricin A chain requires the Png1–Rad23 complex, suggesting that this complex couples protein deglycosylation and degradation. Rad23 is a ubiquitin (Ub) binding protein involved in the transfer of ubiquitylated substrates to the proteasome. How Rad23 achieves its substrate specificity is unknown. We show that Rad23 binds various regulators of proteolysis to facilitate the degradation of distinct substrates. We propose that the substrate specificity of Rad23 and other Ub binding proteins is determined by their interactions with various cofactors involved in specific degradation pathways.

scholarly journals Folding-competent and Folding-defective Forms of Ricin A Chain Have Different Fates after Retrotranslocation from the Endoplasmic Reticulum

2010 ◽  
Vol 21 (15) ◽  
pp. 2543-2554 ◽  
Author(s):  
Shuyu Li ◽  
Robert A. Spooner ◽  
Stuart C. H. Allen ◽  
Christopher P. Guise ◽  
Graham Ladds ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Ubiquitin Ligase ◽  
E3 Ubiquitin Ligase ◽  
Structural Features ◽  
Ricin A Chain ◽  
Golgi Transport ◽  
Ubiquitin Ligase Complex ◽  
A Chain ◽  
Ricin A

We report that a toxic polypeptide retaining the potential to refold upon dislocation from the endoplasmic reticulum (ER) to the cytosol (ricin A chain; RTA) and a misfolded version that cannot (termed RTAΔ), follow ER-associated degradation (ERAD) pathways in Saccharomyces cerevisiae that substantially diverge in the cytosol. Both polypeptides are dislocated in a step mediated by the transmembrane Hrd1p ubiquitin ligase complex and subsequently degraded. Canonical polyubiquitylation is not a prerequisite for this interaction because a catalytically inactive Hrd1p E3 ubiquitin ligase retains the ability to retrotranslocate RTA, and variants lacking one or both endogenous lysyl residues also require the Hrd1p complex. In the case of native RTA, we established that dislocation also depends on other components of the classical ERAD-L pathway as well as an ongoing ER–Golgi transport. However, the dislocation pathways deviate strikingly upon entry into the cytosol. Here, the CDC48 complex is required only for RTAΔ, although the involvement of individual ATPases (Rpt proteins) in the 19S regulatory particle (RP) of the proteasome, and the 20S catalytic chamber itself, is very different for the two RTA variants. We conclude that cytosolic ERAD components, particularly the proteasome RP, can discriminate between structural features of the same substrate.

Ricin A chain utilises the endoplasmic reticulum-associated protein degradation pathway to enter the cytosol of yeast

FEBS Letters ◽  
1999 ◽  
Vol 459 (1) ◽  
pp. 80-84 ◽  
Author(s):  
Jeremy C. Simpson ◽  
Lynne M. Roberts ◽  
Karin Römisch ◽  
John Davey ◽  
Dieter H. Wolf ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Degradation ◽  
Degradation Pathway ◽  
Ricin A Chain ◽  
A Chain ◽  
Ricin A

scholarly journals EDEM Is Involved in Retrotranslocation of Ricin from the Endoplasmic Reticulum to the Cytosol

2006 ◽  
Vol 17 (4) ◽  
pp. 1664-1675 ◽  
Author(s):  
Monika Slominska-Wojewodzka ◽  
Tone F. Gregers ◽  
Sébastien Wälchli ◽  
Kirsten Sandvig
Keyword(s):  
Endoplasmic Reticulum ◽  
Rna Interference ◽  
Cell Surface ◽  
Cellular Level ◽  
Misfolded Proteins ◽  
Plant Toxin ◽  
Ricin A Chain ◽  
Transfected Cells ◽  
A Chain ◽  
Ricin A

The plant toxin ricin is transported retrogradely from the cell surface to the endoplasmic reticulum (ER) from where the enzymatically active part is retrotranslocated to the cytosol, presumably by the same mechanism as used by misfolded proteins. The ER degradation enhancing α-mannosidase I-like protein, EDEM, is responsible for directing aberrant proteins for ER-associated protein degradation. In this study, we have investigated whether EDEM is involved in ricin retrotranslocation. Overexpression of EDEM strongly protects against ricin. However, when the interaction between EDEM and misfolded proteins is inhibited by kifunensin, EDEM promotes retrotranslocation of ricin from the ER to the cytosol. Furthermore, puromycin, which inhibits synthesis and thereby transport of proteins into the ER, counteracted the protection seen in EDEM-transfected cells. Coimmunoprecipitation studies revealed that ricin can interact with EDEM and with Sec61α, and both kifunensin and puromycin increase these interactions. Importantly, vector-based RNA interference against EDEM, which leads to reduction of the cellular level of EDEM, decreased retrotranslocation of ricin A-chain to the cytosol. In conclusion, our results indicate that EDEM is involved in retrotranslocation of ricin from the ER to the cytosol.

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