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Abstract
Protein disulfide isomerase (PDI) is a redox-dependent protein with oxidoreductase and chaperone activities. It is a U-shaped protein with an abb'xa' structural organization in which the a and a' domains have CGHC active sites, the b and b' domains are involved with substrate binding, and x is a flexible linker. PDI exhibits substantial flexibility and undergoes cycles of unfolding and refolding in its interaction with cholera toxin, suggesting PDI can regain a folded, functional conformation after exposure to stress conditions. To determine whether this unfolding-refolding cycle is a substrate-induced process or an intrinsic physical property of PDI, we used circular dichroism to examine the structural properties of PDI subjected to thermal denaturation. PDI exhibited remarkable conformational resilience that is linked to its redox status. In the reduced state, PDI exhibited a 54 °C unfolding transition temperature (Tm) and regained 85% of its native structure after nearly complete thermal denaturation. Oxidized PDI had a lower Tm of 48-50 °C and regained 70% of its native conformation after 75% denaturation. Both reduced PDI and oxidized PDI were functional after refolding from these denatured states. Additional studies documented increased stability of a PDI construct lacking the a' domain and decreased thermal stability of a construct lacking the a domain. Furthermore, oxidation of the a domain limited the ability of PDI to refold. The stability and conformational resilience of PDI are thus linked to both redox-dependent and domain-specific effects. These findings document previously unrecognized properties of PDI and provide insight into the physical foundation of its biological function.
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Affiliation(s)
- Jessica Guyette
- Burnett School of Biomedical Sciences, College of Medicine , University of Central Florida , Orlando , Florida 32816 , United States
| | - Baggio Evangelista
- Burnett School of Biomedical Sciences, College of Medicine , University of Central Florida , Orlando , Florida 32816 , United States
| | - Suren A Tatulian
- Department of Physics , University of Central Florida , Orlando , Florida 32816 , United States
| | - Ken Teter
- Burnett School of Biomedical Sciences, College of Medicine , University of Central Florida , Orlando , Florida 32816 , United States
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Guyette J, Cherubin P, Serrano A, Taylor M, Abedin F, O'Donnell M, Burress H, Tatulian SA, Teter K. Quercetin-3-Rutinoside Blocks the Disassembly of Cholera Toxin by Protein Disulfide Isomerase. Toxins (Basel) 2019; 11:E458. [PMID: 31382673 PMCID: PMC6722528 DOI: 10.3390/toxins11080458] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 07/24/2019] [Accepted: 08/02/2019] [Indexed: 12/11/2022] Open
Abstract
Protein disulfide isomerase (PDI) is mainly located in the endoplasmic reticulum (ER) but is also secreted into the bloodstream where its oxidoreductase activity is involved with thrombus formation. Quercetin-3-rutinoside (Q3R) blocks this activity, but its inhibitory mechanism against PDI is not fully understood. Here, we examined the potential inhibitory effect of Q3R on another process that requires PDI: disassembly of the multimeric cholera toxin (CT). In the ER, PDI physically displaces the reduced CTA1 subunit from its non-covalent assembly in the CT holotoxin. This is followed by CTA1 dislocation from the ER to the cytosol where the toxin interacts with its G protein target for a cytopathic effect. Q3R blocked the conformational change in PDI that accompanies its binding to CTA1, which, in turn, prevented PDI from displacing CTA1 from its holotoxin and generated a toxin-resistant phenotype. Other steps of the CT intoxication process were not affected by Q3R, including PDI binding to CTA1 and CT reduction by PDI. Additional experiments with the B chain of ricin toxin found that Q3R could also disrupt PDI function through the loss of substrate binding. Q3R can thus inhibit PDI function through distinct mechanisms in a substrate-dependent manner.
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Affiliation(s)
- Jessica Guyette
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32816, USA
| | - Patrick Cherubin
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32816, USA
| | - Albert Serrano
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32816, USA
| | - Michael Taylor
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32816, USA
| | - Faisal Abedin
- Department of Physics, College of Sciences, University of Central Florida, Orlando, FL 32816, USA
| | - Morgan O'Donnell
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32816, USA
| | - Helen Burress
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32816, USA
| | - Suren A Tatulian
- Department of Physics, College of Sciences, University of Central Florida, Orlando, FL 32816, USA
| | - Ken Teter
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32816, USA.
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Burress H, Kellner A, Guyette J, Tatulian SA, Teter K. HSC70 and HSP90 chaperones perform complementary roles in translocation of the cholera toxin A1 subunit from the endoplasmic reticulum to the cytosol. J Biol Chem 2019; 294:12122-12131. [PMID: 31221799 DOI: 10.1074/jbc.ra119.008568] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 06/15/2019] [Indexed: 11/06/2022] Open
Abstract
Cholera toxin (CT) travels by vesicle carriers from the cell surface to the endoplasmic reticulum (ER) where the catalytic A1 subunit of CT (CTA1) dissociates from the rest of the toxin, unfolds, and moves through a membrane-spanning translocon pore to reach the cytosol. Heat shock protein 90 (HSP90) binds to the N-terminal region of CTA1 and facilitates its ER-to-cytosol export by refolding the toxin as it emerges at the cytosolic face of the ER membrane. HSP90 also refolds some endogenous cytosolic proteins as part of a foldosome complex containing heat shock cognate 71-kDa protein (HSC70) and the HSC70/HSP90-organizing protein (HOP) linker that anchors HSP90 to HSC70. We accordingly predicted that HSC70 and HOP also function in CTA1 translocation. Inactivation of HSC70 by drug treatment disrupted CTA1 translocation to the cytosol and generated a toxin-resistant phenotype. In contrast, the depletion of HOP did not disrupt CT activity against cultured cells. HSC70 and HSP90 could bind independently to disordered CTA1, even in the absence of HOP. This indicated HSP90 and HSC70 recognize distinct regions of CTA1, which was confirmed by the identification of a YYIYVI-binding motif for HSC70 that spans residues 83-88 of the 192-amino acid CTA1 polypeptide. Refolding of disordered CTA1 occurred in the presence of HSC70 alone, indicating that HSC70 and HSP90 can each independently refold CTA1. Our work suggests a novel translocation mechanism in which sequential interactions with HSP90 and HSC70 drive the N- to C-terminal extraction of CTA1 from the ER.
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Affiliation(s)
- Helen Burress
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida 32826
| | - Alisha Kellner
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida 32826
| | - Jessica Guyette
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida 32826
| | - Suren A Tatulian
- Department of Physics, University of Central Florida, Orlando, Florida 32816
| | - Ken Teter
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida 32826.
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Guyette J, Evangelista B, Tatulian SA, Teter K. Conformational Resilience of Protein Disulfide Isomerase. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.780.3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | - Ken Teter
- University of Central FloridaOrlandoFL
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Cherubin P, Garcia MC, Curtis D, Britt CBT, Craft JW, Burress H, Berndt C, Reddy S, Guyette J, Zheng T, Huo Q, Quiñones B, Briggs JM, Teter K. Inhibition of Cholera Toxin and Other AB Toxins by Polyphenolic Compounds. PLoS One 2016; 11:e0166477. [PMID: 27829022 PMCID: PMC5102367 DOI: 10.1371/journal.pone.0166477] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 10/28/2016] [Indexed: 01/09/2023] Open
Abstract
Cholera toxin (CT) is an AB-type protein toxin that contains a catalytic A1 subunit, an A2 linker, and a cell-binding B homopentamer. The CT holotoxin is released into the extracellular environment, but CTA1 attacks a target within the cytosol of a host cell. We recently reported that grape extract confers substantial resistance to CT. Here, we used a cell culture system to identify twelve individual phenolic compounds from grape extract that inhibit CT. Additional studies determined the mechanism of inhibition for a subset of the compounds: two inhibited CT binding to the cell surface and even stripped CT from the plasma membrane of a target cell; two inhibited the enzymatic activity of CTA1; and four blocked cytosolic toxin activity without directly affecting the enzymatic function of CTA1. Individual polyphenolic compounds from grape extract could also generate cellular resistance to diphtheria toxin, exotoxin A, and ricin. We have thus identified individual toxin inhibitors from grape extract and some of their mechanisms of inhibition against CT.
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Affiliation(s)
- Patrick Cherubin
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - Maria Camila Garcia
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - David Curtis
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - Christopher B. T. Britt
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - John W. Craft
- Department of Biology & Biochemistry, University of Houston, Houston, Texas, United States of America
| | - Helen Burress
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - Chris Berndt
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - Srikar Reddy
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - Jessica Guyette
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
| | - Tianyu Zheng
- NanoScience Technology Center and Department of Chemistry, University of Central Florida, Orlando, Florida, United States of America
| | - Qun Huo
- NanoScience Technology Center and Department of Chemistry, University of Central Florida, Orlando, Florida, United States of America
| | - Beatriz Quiñones
- Produce Safety and Microbiology Research Unit, Western Regional Research Center, United States Department of Agriculture - Agricultural Research Service, Albany, California, United States of America
| | - James M. Briggs
- Department of Biology & Biochemistry, University of Houston, Houston, Texas, United States of America
| | - Ken Teter
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America
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