Calmodulin fishing with a structurally disordered bait triggers CyaA catalysis

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

Edité par CCSD ; Public Library of Science -

International audience. 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.

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