Functional and structural studies on different forms of the adenylate cyclase toxin of Bordetella pertussis

Cheung, G.Y.C., Kelly, S.M. , Jess, T.J., Prior, S., Price, N.C., Parton, R.G. and Coote, J.G. (2009) Functional and structural studies on different forms of the adenylate cyclase toxin of Bordetella pertussis. Microbial Pathogenesis, 46(1), pp. 36-42. (doi:10.1016/j.micpath.2008.10.005)

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A comparison was made of the cytotoxic activity and secondary structural features of four recombinant forms of adenylate cyclase toxin (CyaA). These forms were fully functional CyaA, CyaA lacking adenylate cyclase enzymatic activity (CyaA*), and non-acylated forms of these toxins, proCyaA and proCyaA*. At a toxin concentration >1 μg/ml, CyaA* was as cytotoxic towards J774.2 cells as CyaA and mediated cell killing at a faster rate than CyaA. At concentrations <0.5 μg/ml, CyaA* was less cytotoxic than CyaA and, at <0.1 μg/ml of CyaA*, no activity was detected. CyaA, but not CyaA*, was able to induce caspase 3/7 activity, a measure of apoptosis. ProCyaA and proCyaA* had no detectable cytotoxic or apoptotic activity. CyaA caused 50% inhibition of the zymosan-stimulated oxidative burst at 0.003 μg/ml, whereas a not, vert, similar500-fold greater toxin concentration of CyaA* or proCyaA was needed for 50% inhibition. ProCyaA* was inactive. CyaA is a calcium-binding protein and far UV circular dichroism (CD), near UV CD and fluorescence spectra analyses showed that all the forms of CyaA had similar overall structures at different calcium concentrations up to 5.0 mM. At 7.5 mM CaCl2, the far UV spectrum of CyaA altered significantly, indicating a change in secondary structure associated with high β-sheet content or a β-aggregated state, whereas the spectrum of CyaA* showed only a slight alteration at this calcium concentration. Near UV CD and fluorescence studies were consistent with a rearrangement of secondary structural elements in the presence of CaCl2 for all CyaA forms. There was a marked dependence on protein concentration of the far UV spectra of these CyaA forms, implying an interaction between individual molecules at higher protein concentrations.

Item Type:Articles
Keywords:Bordetella pertussis, adenylate cyclase toxin, CyaA, cytotoxicity, secondary structure, circular dichroism
Glasgow Author(s) Enlighten ID:Coote, Professor John and Parton, Dr Roger and Price, Prof Nicholas and Kelly, Dr Sharon
Authors: Cheung, G.Y.C., Kelly, S.M., Jess, T.J., Prior, S., Price, N.C., Parton, R.G., and Coote, J.G.
Subjects:Q Science > QR Microbiology
College/School:College of Medical Veterinary and Life Sciences
College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
Journal Name:Microbial Pathogenesis

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