Adenylate cyclase toxin-hemolysin (CyaA, ACT or AC-Hly) of the whooping cough agent Bordetella pertussis penetrates phagocytes expressing the integrin complement receptor 3 (CR3, CD11b/CD18, α(M)β(2) or Mac-1). CyaA translocates its adenylate cyclase (AC) enzyme domain into cell cytosol and catalyzes unregulated conversion of ATP to cAMP, thereby subverting cellular signaling. In parallel, CyaA forms small cation-selective membrane pores that permeabilize cells for potassium efflux, contributing to cytotoxicity of CyaA and eventually provoking colloid-osmotic cell lysis. To investigate whether the single-pass α-helical transmembrane segments of CR3 subunits CD11b and CD18 do directly participate in AC domain translocation and/or pore formation by the toxin, we expressed in CHO cells variants of CR3 that contained artificial transmembrane segments, or lacked the transmembrane segment(s) at all. The results demonstrate that the transmembrane segments of CR3 are not directly involved in the cytotoxic activities of CyaA but serve for maintaining CR3 in a conformation that is required for efficient toxin binding and action.

Institute of Analytical Chemistry of the CAS v v i Veveri 97 602 00 Brno Czech Republic

Institute of Microbiology of the CAS v v i Videnska 1083 142 20 Prague 4 Czech Republic

Institute of Microbiology of the CAS v v i Videnska 1083 142 20 Prague 4 Czech Republic Department of Biochemistry Faculty of Science Charles University Prague Hlavova 8 128 43 Prague 2 Czech Republic

Institute of Microbiology of the CAS v v i Videnska 1083 142 20 Prague 4 Czech Republic Department of Genetics and Microbiology Faculty of Science Charles University Prague Vinicna 5 128 44 Prague 2 Czech Republic

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