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Adenylate cyclase toxin (ACT) is one of the main virulence factors of Bordetella pertussis , with crucial role in colonization of human respiratory tract. ACT toxicity on target phagocytes results from translocation of its adenylate cyclase domain and production of high cAMP levels and from pore formation. Recently, we unveiled in ACT four cholesterol-recognition motifs involved in specific interaction with membrane cholesterol, which might stabilize membrane topology of critical helices for ACT activity. Here we explore an amphipathic peptide corresponding to ACT residues 454 to 487 containing one of such CRAC motifs. We show that P454-487 penetrates into DOPC vesicles as a long and tilted α-helix, while in cholesterol presence experiments conformational changes that critically depend on the CRAC Phe-485 residue. Moreover, P454-487 is capable of blocking ACT toxicity on cells by outcompeting with the full-length toxin for membrane binding. We anticipate P454-487 may have potential clinical applicability in controlling Bordetella infection.