Unfolded cholera toxin is transferred to the ER membrane and released from protein disulfide isomerase upon oxidation by Ero1.
The toxic effect of cholera toxin (CT) on target cells is caused by its A1 chain. This polypeptide is released from the holotoxin and unfolded in the lumen of the ER by the action of protein disulfide isomerase (PDI), before being retrotranslocated into the cytosol. The polypeptide is initially unfolded by binding to the reduced form of PDI. We show that upon oxidation of the COOH-terminal disulfide bond in PDI by the enzyme Ero1, the A1 chain is released. Both yeast Ero1 and the mammalian Ero1alpha isoform are active in this reaction. Ero1 has a preference for the PDI-toxin complex. We further show that the complex is transferred to a protein at the lumenal side of the ER membrane, where the unfolded toxin is released from PDI by the action of Ero1. Taken together, our results identify Ero1 as the enzyme mediating the release of unfolded CT from PDI and characterize an additional step in retrotranslocation of the toxin.
Tsai
Billy
B
Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
Rapoport
Tom A
TA
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002772:Cholera Toxin / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D010084:Oxidation-Reduction; D050862:Oxidoreductases Acting on Sulfur Group Donors; D011485:Protein Binding / Q000502:physiology; D019704:Protein Disulfide-Isomerases / Q000378:metabolism*; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins; D015003:Yeasts
D006023:Glycoproteins; D029701:Saccharomyces cerevisiae Proteins; D002772:Cholera Toxin; D050862:Oxidoreductases Acting on Sulfur Group Donors; C113186:ERO1 protein, S cerevisiae; D019704:Protein Disulfide-Isomerases