Structural Consequences of Divalent Metal Binding by the Adenylyl Cyclase Toxin of Bordetella pertussis

Structure and function of RTX toxins

“…CyaA contains about 40 RTX motifs and binds, in solution, about 40 calcium ions with an affinity in the submillimolar range (i.e., 0.1 to 1 mM [7,71,[77][78][79]), while HlyA, which has 11-13 RTX repeats, can bind up to 12 calcium ions [80]. This indicates a binding stoichiometry of one calcium ion per RTX motif.…”

Molecular Pathogenesis, Epidemiology, and Clinical Manifestations of Respiratory Infections Due toBordetella pertussisand OtherBordetellaSubspecies

“…The 1,300-aminoacid C-terminal domain mediates delivery of the catalytic domain into the cytoplasm of eukaryotic cells and possesses low but detectable hemolytic activity for sheep red blood cells (46,349,668). Amino acid sequence similarity between the Cterminal domain of CyaA, the hemolysins of E. coli (HlyA) and Actinobacillus pleuropneumoniae (HppA), and the leukotoxins of Pasteurella hemolytica (LktA) and Actinobacillus actinomycetemcomitans (AaLtA) places CyaA within a family of calcium-dependent, pore-forming cytotoxins known as RTX (repeats-in-toxin) toxins (659,672,676,813). Each of these toxins contains a tandem array of a nine amino acid repeat [LXGG XG(N/D)DX] that is thought to be involved in calcium binding (813).…”

Bordetella protein toxins

“…CyaA harbors about 40 calcium-binding sites, and already a seemingly irreversible loading of about 5 Ca 2+ binding sites allows the toxin to interact with membranes and to express hemolytic activity [128,130]. The precise location of these high-affinity binding sites within the Hly moiety of CyaA remains unknown, while the low-affinity (K d > 0.3 mM) Ca 2+ binding sites (about 35-40) have been located within the 700 C-terminal residues of CyaA [130,134]. The recently determined crystal structure of RTX blocks IV and V of CyaA demonstrates that the calcium atoms bind to CyaA within the turns connecting adjacent antiparallel beta strands formed by the X-(L/I/F)-X-G-G-X-G-(N/D)-D nonapeptides of the RTX domain (Bumba et al, unpublished results).…”

“…It contains (i) a hydrophobic pore-forming domain comprising residues 500-700 [121]; (ii) an activation domain between residues 800 and 1000, where the posttranslational palmitoylation of CyaA occurs [132,133]; and (iii) a typical calciumbinding RTX domain harboring the more-or-less conserved nonapeptide repeats of a consensus sequence X-(L/I/F)-X-G-G-X-G-(N/D)-D, which form about 40 calciumbinding sites [130,134]. In the presence of calcium, the whole RTX domain exhibits a stable and compact β-sheet conformation that is required for efficient binding on target cells [135].…”