Speaker: Alexandre Chenal
Biochemistry of Macromolecular Interactions unit, Structural Biology and Chemistry Department, Institut Pasteur, Paris, France
Title: Structural flexibility of the CyaA toxin is critical from its secretion to host cell intoxication
Abstract:
Bordetella pertussis, the causative agent of whooping cough, secretes an adenylate cyclase toxin, CyaA, a 1706-residue RTX protein essential for the early stages of colonizing the human respiratory tract. Although CyaA-mediated cell intoxication is central to B. pertussis pathogenicity, this process has remained poorly understood. Following secretion by a type I secretion system, CyaA intoxicates human target cells by directly translocating its catalytic domain (ACD) across the plasma membrane. We show that the CyaA translocation region (TR) exhibits an intrinsic propensity to translocate across membranes and to bind endogenous calmodulin (CaM) with high affinity, thereby favoring ACD translocation. Once in the cytosol, ACD refolds upon CaM binding and catalyzes the production of high levels of cAMP, ultimately leading to cell death. Our combined biophysical and integrative modeling approaches reveal that the structural flexibility of CyaA is crucial for its secretion, folding, membrane translocation, and subsequent cell intoxication. These sequential steps rely on disorder-to-order conformational transitions that are finely tuned to the environmental conditions CyaA encounters on its journey from the bacterium to the eukaryotic cytoplasm. Moreover, high-resolution structural characterization of CyaA has long been hindered by its size, multi-domain organization, flexibility, and aggregation propensity. We have recently overcome these challenges and obtained the first structural ensembles of both non-acylated and acylated CyaA in solution by integrating diverse experimental data with advanced AI-guided modeling. Together, these findings open new perspectives for basic research and biotechnological applications, positioning recombinant CyaA proteins as promising antigen delivery vehicles and as a potential protective antigen for the next generation of pertussis vaccines.
Invited by Marielle Valerio-Lepiniec
