Abstract
The adenylate cyclase toxin-hemolysin (CyaA, ACT, or AC-Hly) plays a crucial role in virulence and airway colonization capacity of the whooping cough agent Bordetella pertussis. The toxin penetrates target cell membranes and exhibits three distinct biological activities. A population of CyaA conformers forms small cation-selective pores that permeabilize the cell membrane for potassium efflux, which can provoke colloid-osmotic (oncotic) cell lysis. The other two activities are due to CyaA conformers that transiently form calcium influx conduits in the target cell membrane and translocate the adenylate cyclase (AC) enzyme into cytosol of cells. A fourth putative biological activity has recently been reported; an intrinsic phospholipase A (PLA) activity was claimed to be associated with the CyaA polypeptide and be involved in the mechanism of translocation of the AC enzyme polypeptide across cell membrane lipid bilayer. However, the conclusions drawn by the authors contradicted their own results and we show them to be erroneous. We demonstrate that highly purified CyaA is devoid of any detectable phospholipase A1 activity and that contrary to the published claims, the two putative conserved phospholipase A catalytic residues, namely the Ser606 and Asp1079 residues, are not involved in the process of membrane translocation of the AC domain of CyaA across target membranes.
Highlights
The adenylate cyclase toxin-hemolysin (ACT, AC-hemolysin moiety (Hly), or CyaA) is a key virulence factor of Bordetellae that are pathogenic to mammals [1]
CyaA is a multifunctional protein (1706 residues) that consists of an N-terminal enzymatic adenylate cyclase (AC) domain of 384 residues that is fused to a pore-forming RTX hemolysin moiety (Hly) of 1322 residues by an AC-to-Hly-linker segment [5,6,7]
We showed that a membrane translocation intermediate of the AC domain itself participates in the formation of a novel type of conduit that mediates the influx of extracellular calcium ions across the plasma membrane of monocytic cells [27]
Summary
The adenylate cyclase toxin-hemolysin (ACT, AC-Hly, or CyaA) is a key virulence factor of Bordetellae that are pathogenic to mammals [1]. N-linked oligosaccharides [12,13], the CyaA recognizes a specific segment of the CD11b subunit of CR3 [11], which positions it for efficient insertion into the phagocyte membrane and enables the toxin molecule to directly deliver its N-terminal AC domain across the cytoplasmic membrane into the cytosol of the cell, without the need for receptor-mediated endocytic uptake of the toxin [10,14,15,16,17,18,19,20]. Gonzáles-Bullón et al [36] reported that in addition to pore-forming, calcium-conducting, and AC-translocating activities, the CyaA polypeptide possesses an intrinsic calcium-dependent phospholipase A (PLA) activity This was proposed to be directly involved in the translocation of the AC domain of CyaA across PLA-formed toroidal pores within the lipid bilayer of the cellular membrane. The results reported here clearly show that a highly purified and fully biologically active CyaA toxin is devoid of any detectable intrinsic PLA-1 enzyme activity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
