Structure–Function Relationships Underlying the Capacity of Bordetella Adenylate Cyclase Toxin to Disarm Host Phagocytes

Abstract

Bordetellae, pathogenic to mammals, produce an immunomodulatory adenylate cyclase toxin–hemolysin (CyaA, ACT or AC-Hly) that enables them to overcome the innate immune defense of the host. CyaA subverts host phagocytic cells by an orchestrated action of its functional domains, where an extremely catalytically active adenylyl cyclase enzyme is delivered into phagocyte cytosol by a pore-forming repeat-in-toxin (RTX) cytolysin moiety. By targeting sentinel cells expressing the complement receptor 3, known as the CD11b/CD18 (αMβ2) integrin, CyaA compromises the bactericidal functions of host phagocytes and supports infection of host airways by Bordetellae. Here, we review the state of knowledge on structural and functional aspects of CyaA toxin action, placing particular emphasis on signaling mechanisms by which the toxin-produced 3′,5′-cyclic adenosine monophosphate (cAMP) subverts the physiology of phagocytic cells.

A high-affinity calmodulin-binding site in the CyaA toxin translocation domain is essential for invasion into eukaryotic cells

“…The adenylate cyclase (CyaA) toxin is a major virulence factor produced by Bordetella pertussis, the causative agent of whooping cough, and is involved in the early stages of respiratory tract colonization [1][2][3][4][5] . CyaA, a 1706-residue long protein ( Figure S1), is a Repeatin-ToXin (RTX) [6][7][8][9][10] multi-domain toxin [11][12] .…”

“…The translocation region (TR, residues 365 to 527) is essential for AC translocation into target cells 17 . The hydrophobic region (HR, residues 528 to 710) inserts into the cell membrane and makes cation-selective pores 10,[18][19] ; the acylation region (AR, residues 711 to 1005) contains two post-translational acylation sites, at lysines K860 and K983 [20][21][22] , required for the refolding of the CyaA toxin 12,23 and AC translocation across membranes in vivo and in vitro 5,[20][21]24 . The cell-receptor binding domain of CyaA (RD, residues 1006 to 1706) is made up of approximately 40 copies of calcium-binding RTX motifs [8][9][10]25 .…”

“…Accumulation of supraphysiologic levels of cAMP in target cells alters their phagocytic functions leading to host defense subversion 5,11,[59][60] .…”

Post‐translational acylation controls the folding and functions of the CyaA RTX toxin

“…It is well known that acylation is critically required for the pore-forming activity of CyaA as well as its ability to invade cells to produce high levels of cAMP (i.e., cell intoxication) (45,46). Here, we have analyzed the structural and hydrodynamic properties of both pro-CyaA and CyaA monomers to provide insights into their folding process and to identify the structural basis of the acylation-dependent gain of functions.…”

An Introduction to the Toxins Special Issue on the Adenylate Cyclase Toxin

“…Jakub Novak et al and Helena Ostolaza et al provide two complementary reviews describing the molecular basis of CyaA biogenesis and translocation. Novak and colleagues further highlight the diverse effects of CyaA on host phagocytes [ 5 ], while the Ostolaza group provides a detailed description of the potential molecular processes leading to CyaA translocation across the plasma membrane of target cells [ 6 ].…”