ADP-ribosylation factor 6 acts as an allosteric activator for the folded but not disordered cholera toxin A1 polypeptide

    Authors

    T. Banerjee; M. Taylor; M. G. Jobling; H. Burress; Z. J. Yang; A. Serrano; R. K. Holmes; S. A. Tatulian;K. Teter

    Comments

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    Abbreviated Journal Title

    Mol. Microbiol.

    Keywords

    RETICULUM-ASSOCIATED DEGRADATION; CHO-CELLS RESISTANT; ENDOPLASMIC-RETICULUM; LIPID RAFTS; NUCLEOTIDE EXCHANGE; RETRO-TRANSLOCATION; PROTEIN COFACTOR; BOVINE BRAIN; SUBUNIT; BINDING; Biochemistry & Molecular Biology; Microbiology

    Abstract

    The catalytic A1 subunit of cholera toxin (CTA1) has a disordered structure at 37 degrees C. An interaction with host factors must therefore place CTA1 in a folded conformation for the modification of its Gs target which resides in a lipid raft environment. Host ADP-ribosylation factors (ARFs) act as in vitro allosteric activators of CTA1, but the molecular events of this process are not fully characterized. Isotope-edited Fourier transform infrared spectroscopy monitored ARF6-induced structural changes to CTA1, which were correlated to changes in CTA1 activity. We found ARF6 prevents the thermal disordering of structured CTA1 and stimulates the activity of stabilized CTA1 over a range of temperatures. Yet ARF6 alone did not promote the refolding of disordered CTA1 to an active state. Instead, lipid rafts shifted disordered CTA1 to a folded conformation with a basal level of activity that could be further stimulated by ARF6. Thus, ARF alone is unable to activate disordered CTA1 at physiological temperature: additional host factors such as lipid rafts place CTA1 in the folded conformation required for its ARF-mediated activation. Interaction with ARF is required for in vivo toxin activity, as enzymatically active CTA1 mutants that cannot be further stimulated by ARF6 fail to intoxicate cultured cells.

    Journal Title

    Molecular Microbiology

    Volume

    94

    Issue/Number

    4

    Publication Date

    1-1-2014

    Document Type

    Article

    Language

    English

    First Page

    898

    Last Page

    912

    WOS Identifier

    WOS:000344871800014

    ISSN

    0950-382X

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