PLoS Biology (Dec 2017)

Calmodulin fishing with a structurally disordered bait triggers CyaA catalysis.

  • Darragh P O'Brien,
  • Dominique Durand,
  • Alexis Voegele,
  • Véronique Hourdel,
  • Marilyne Davi,
  • Julia Chamot-Rooke,
  • Patrice Vachette,
  • Sébastien Brier,
  • Daniel Ladant,
  • Alexandre Chenal

DOI
https://doi.org/10.1371/journal.pbio.2004486
Journal volume & issue
Vol. 15, no. 12
p. e2004486

Abstract

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Once translocated into the cytosol of target cells, the catalytic domain (AC) of the adenylate cyclase toxin (CyaA), a major virulence factor of Bordetella pertussis, is potently activated by binding calmodulin (CaM) to produce supraphysiological levels of cAMP, inducing cell death. Using a combination of small-angle X-ray scattering (SAXS), hydrogen/deuterium exchange mass spectrometry (HDX-MS), and synchrotron radiation circular dichroism (SR-CD), we show that, in the absence of CaM, AC exhibits significant structural disorder, and a 75-residue-long stretch within AC undergoes a disorder-to-order transition upon CaM binding. Beyond this local folding, CaM binding induces long-range allosteric effects that stabilize the distant catalytic site, whilst preserving catalytic loop flexibility. We propose that the high enzymatic activity of AC is due to a tight balance between the CaM-induced decrease of structural flexibility around the catalytic site and the preservation of catalytic loop flexibility, allowing for fast substrate binding and product release. The CaM-induced dampening of AC conformational disorder is likely relevant to other CaM-activated enzymes.