title: Derlin-1 facilitates the retro-translocation of cholera toxin.
abstract: Cholera toxin (CT) intoxicates cells by using its receptor-binding B subunit (CTB) to traffic from the plasma membrane to the endoplasmic reticulum (ER). In this compartment, the catalytic A1 subunit (CTA1) is unfolded by protein disulfide isomerase (PDI) and retro-translocated to the cytosol where it triggers a signaling cascade, leading to secretory diarrhea. How CT is targeted to the site of retro-translocation in the ER membrane to initiate translocation is unclear. Using a semipermeabilized-cell retro-translocation assay, we demonstrate that a dominant-negative Derlin-1-YFP fusion protein attenuates the ER-to-cytosol transport of CTA1. Derlin-1 interacts with CTB and the ER chaperone PDI as assessed by coimmunoprecipitation experiments. An in vitro membrane-binding assay showed that CTB stimulated the unfolded CTA1 chain to bind to the ER membrane. Moreover, intoxication of intact cells with CTB stabilized the degradation of a Derlin-1-dependent substrate, suggesting that CT uses the Derlin-1 pathway. These findings indicate that Derlin-1 facilitates the retro-translocation of CT. CTB may play a role in this process by targeting the holotoxin to Derlin-1, enabling the Derlin-1-bound PDI to unfold the A1 subunit and prepare it for transport.
authors: Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
authors: Kaleena M
authors: KM
authors: Bernardi
authors: Michele L
authors: ML
authors: Forster
authors: Wayne I
authors: WI
authors: Lencer
authors: Billy
authors: B
authors: Tsai
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D002460:Cell Line; D002772:Cholera Toxin / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; C487709:DERL1 protein, human; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C054562:yellow fluorescent protein, Bacteria; D002772:Cholera Toxin; D019704:Protein Disulfide-Isomerases