title: A therapeutic chemical chaperone inhibits cholera intoxication and unfolding/translocation of the cholera toxin A1 subunit.
abstract: Cholera toxin (CT) travels as an intact AB(5) protein toxin from the cell surface to the endoplasmic reticulum (ER) of an intoxicated cell. In the ER, the catalytic A1 subunit dissociates from the rest of the toxin. Translocation of CTA1 from the ER to the cytosol is then facilitated by the quality control mechanism of ER-associated degradation (ERAD). Thermal instability in the isolated CTA1 subunit generates an unfolded toxin conformation that acts as the trigger for ERAD-mediated translocation to the cytosol. In this work, we show by circular dichroism and fluorescence spectroscopy that exposure to 4-phenylbutyric acid (PBA) inhibited the thermal unfolding of CTA1. This, in turn, blocked the ER-to-cytosol export of CTA1 and productive intoxication of either cultured cells or rat ileal loops. In cell culture studies PBA did not affect CT trafficking to the ER, CTA1 dissociation from the holotoxin, or functioning of the ERAD system. PBA is currently used as a therapeutic agent to treat urea cycle disorders. Our data suggest PBA could also be used in a new application to prevent or possibly treat cholera.
authors.affiliation: Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Taylor
authors.forename: Tuhina
authors.initials: T
authors.lastname: Banerjee
authors.forename: Fernando
authors.initials: F
authors.lastname: Navarro-Garcia
authors.forename: Jazmin
authors.initials: J
authors.lastname: Huerta
authors.forename: Shane
authors.initials: S
authors.lastname: Massey
authors.forename: Mansfield
authors.initials: M
authors.lastname: Burlingame
authors.forename: Abhay H
authors.initials: AH
authors.lastname: Pande
authors.forename: Suren A
authors.initials: SA
authors.lastname: Tatulian
authors.forename: Ken
authors.initials: K
authors.lastname: Teter
mesh_terms: D000818:Animals; D002771:Cholera / Q000188:drug therapy*; D002772:Cholera Toxin / Q000378:metabolism / Q000633:toxicity*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007082:Ileum / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010654:Phenylbutyrates / Q000494:pharmacology* / Q000627:therapeutic use*; D011485:Protein Binding / Q000187:drug effects; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism / Q000633:toxicity*; D021381:Protein Transport / Q000187:drug effects; D058767:Protein Unfolding / Q000187:drug effects*; D051381:Rats; D013696:Temperature
chemical_list: D004220:Disulfides; D010654:Phenylbutyrates; D021122:Protein Subunits; C075773:4-phenylbutyric acid; D002772:Cholera Toxin; D019704:Protein Disulfide-Isomerases