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ADP ‐ribosylation factor 6 acts as an allosteric activator for the folded but not disordered cholera toxin A 1 polypeptide
Author(s) -
Banerjee Tuhina,
Taylor Michael,
Jobling Michael G.,
Burress Helen,
Yang ZhiJie,
Serrano Albert,
Holmes Randall K.,
Tatulian Suren A.,
Teter Ken
Publication year - 2014
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.12807
Subject(s) - cholera toxin , adp ribosylation factor , allosteric regulation , lipid raft , biology , mutant , protein–protein interaction , microbiology and biotechnology , biophysics , biochemistry , enzyme , signal transduction , gene , golgi apparatus , endoplasmic reticulum
Summary The catalytic A 1 subunit of cholera toxin ( CTA1 ) has a disordered structure at 37°C. An interaction with host factors must therefore place CTA1 in a folded conformation for the modification of its Gs α 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 F ourier 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.