Protein disulfide isomerase–like proteins play opposing roles during retrotranslocation

Forster, Michele L.; Sivick, Kelsey E.; Park, Young-nam; Arvan, Peter; Lencer, Wayne I.; Tsai, Billy

doi:10.1083/jcb.200602046

Cited by 108 publications

(147 citation statements)

References 20 publications

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“…S4). These results demonstrate that the PDIinduced shift of CTA1 to a protease-sensitive conformation, which has been interpreted as an unfolding event (9,13,23,28,29), does not correlate to the PDI-induced separation of CTA1 from CTA2/CTB 5 .…”

Section: Discussionmentioning

confidence: 71%

“…The unfoldase activity of PDI in this process is, to the best of our knowledge, a unique property that has not been reported for PDI interactions with any other substrate. Furthermore, the proposed unfoldase activity of PDI is based upon a protease sensitivity assay that only serves as an indirect measure of protein folding (9,13,23,28,29). In this work, we demonstrated that PDI is required for disassembly of the CT holotoxin but does not unfold the CTA1 subunit.…”

Section: Discussionmentioning

confidence: 77%

“…Unfortunately, interpretation of these experiments is complicated by the conformational shift in CTA1 that occurs upon its separation from the holotoxin and by the unstable, heat-labile nature of the free A1 subunit (17). Protease concentration can also affect the outcome of the experiment, as can the temperature of the experiment (17,26,28). It should be noted that most experiments to monitor the "unfoldase" activity of PDI have been performed at 30°C (9,13,23,29), but incubation of CTA1 alone at 37°C will induce the toxin to assume a protease-sensitive conformation (17, 26) (supplemental Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The prevailing model of PDI-toxin interactions is largely based upon the results of a protease sensitivity assay which demonstrated that CTA1 shifts from a protease-resistant conformation to a protease-sensitive conformation in the presence of reduced PDI (9,13,23,28,29). As folded proteins are generally more resistant to proteolysis than unfolded variants of the same protein, this shift was interpreted to represent the PDI-induced unfolding of CTA1 and the PDI-induced displacement of CTA1 from CTA2/CTB 5 .…”

Section: Cholera Toxin (Ct)mentioning

confidence: 99%

See 3 more Smart Citations

Protein-disulfide Isomerase Displaces the Cholera Toxin A1 Subunit from the Holotoxin without Unfolding the A1 Subunit

Taylor

Banerjee

Ray

et al. 2011

Journal of Biological Chemistry

127

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Protein-disulfide isomerase (PDI) has been proposed to exhibit an "unfoldase" activity against the catalytic A1 subunit of cholera toxin (CT). Unfolding of the CTA1 subunit is thought to displace it from the CT holotoxin and to prepare it for translocation to the cytosol. To date, the unfoldase activity of PDI has not been demonstrated for any substrate other than CTA1. An alternative explanation for the putative unfoldase activity of PDI has been suggested by recent structural studies demonstrating that CTA1 will unfold spontaneously upon its separation from the holotoxin at physiological temperature. Thus, PDI may simply dislodge CTA1 from the CT holotoxin without unfolding the CTA1 subunit. To evaluate the role of PDI in CT disassembly and CTA1 unfolding, we utilized a real-time assay to monitor the PDI-mediated separation of CTA1 from the CT holotoxin and directly examined the impact of PDI binding on CTA1 structure by isotope-edited Fourier transform infrared spectroscopy. Our collective data demonstrate that PDI is required for disassembly of the CT holotoxin but does not unfold the CTA1 subunit, thus uncovering a new mechanism for CTA1 dissociation from its holotoxin. Cholera toxin (CT)2 is an AB 5 protein toxin that consists of a catalytic A moiety and a cell-binding B moiety (1, 2). The B subunit is pentameric ring-like structure that adheres to GM1 gangliosides on the plasma membrane of a target cell. The A subunit is initially synthesized as a 26 kDa protein that undergoes proteolytic nicking to generate a disulfide-linked A1/A2 heterodimer. The 21 kDa CTA1 polypeptide is an ADP-ribosyltransferase that modifies and activates Gs␣ in the host cell cytosol. CTA1 can be divided into three subdomains: the A1 1 subdomain contains the catalytic core of the toxin; the A1 2 subdomain is a short extended linker that connects the A1 1 and A1 3 subdomains; and the A1 3 subdomain is a globular structure with many hydrophobic residues as well as a cysteine residue involved with the single disulfide bridge between CTA1 and CTA2 (3). The 5 kDa CTA2 polypeptide maintains numerous non-covalent interactions with the central pore of the B pentamer and thereby anchors CTA1 to CTB 5 . A ribbon diagram of the CT holotoxin which highlights the subdomain structure of CTA1 is provided in supplemental Fig. S1.To reach its cytosolic Gs␣ target, CT moves from the cell surface to the endoplasmic reticulum (ER) by retrograde vesicular traffic (4). A C-terminal KDEL sequence in the CTA2 subunit is thought to target and/or retain CT in the ER (4, 5). Conditions in the ER lead to reductive cleavage of the CTA1/CTA2 disulfide bond and chaperone-assisted dissociation of CTA1 from CTA2/CTB 5 (6 -9). Unfolding of the free A1 subunit then activates the quality control system of ER-associated degradation (ERAD), thereby promoting CTA1 translocation to the cytosol (10, 11). Most exported ERAD substrates are degraded by the ubiquitin-proteasome system, but it was hypothesized that CTA1 and the A chains of other ER-translocating toxins avoid t...

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Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Cholera Toxin (Ct)mentioning

confidence: 99%

See 2 more Smart Citations

Protein-disulfide Isomerase Displaces the Cholera Toxin A1 Subunit from the Holotoxin without Unfolding the A1 Subunit

Taylor

Banerjee

Ray

et al. 2011

Journal of Biological Chemistry

127

View full text Add to dashboard Cite

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“…The same set of factors participating in protein folding and assembly, such as immunoglobulin binding protein (BiP), calnexin, and the family of protein disulfide isomerases, is involved in recognition and retention of folding-defective products [50][51][52].…”

Section: Eradmentioning

confidence: 99%

Genesis of ER stress in Huntington’s Disease

Shenkman

Eiger

Lederkremer

2015

Endoplasmic Reticulum Stress in Diseases

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Recent research has identified ER stress as a major mechanism implicated in cytotoxicity in many neurodegenerative diseases, among them Huntington’s disease. This genetic disorder is of late-onset, progressive and fatal, affecting cognition and movement. There is presently no cure nor any effective therapy for the disease. This review focuses on recent findings that shed light on the mechanisms of the advent and development of ER stress in Huntington’s disease and on its implications, highlighting possible therapeutic avenues that are being or could be explored.

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