title: Adenylate cyclase toxin from Bordetella pertussis. Conformational change associated with toxin activity.
abstract: Adenylate cyclase (AC) toxin from Bordetella pertussis interacts with and enters eukaryotic cells to catalyze the production of supraphysiologic levels of cyclic AMP. Although the calmodulin-activated enzymatic activity (ability to convert ATP to cyclic AMP in a cell-free assay) of this molecule is calcium independent, its toxin activity (ability to increase cyclic AMP levels in intact target cells) requires extracellular calcium. Toxin activity as a function of calcium concentration is biphasic, with no intoxication occurring in the absence of calcium, low level intoxication (200-300 pmol of cyclic AMP/mg of Jurkat cell protein) occurring with free calcium concentrations between 100 nM and 100 microM and a 10-fold increase in AC toxin activity at free calcium concentrations above 300 microM. The molecule exhibits a conformational change when free calcium concentrations exceed 100 microM as demonstrated by shift in intrinsic tryptophan fluorescence, an alteration in binding of one anti-AC monoclonal antibody, protection of a fragment from trypsin-mediated proteolysis, and a structural modification as illustrated by electron microscopy. Thus, it appears that an increase in the ambient calcium concentration to a critical point and the ensuing interaction of the toxin with calcium induces a conformational change which is necessary for its insertion into the target cell and for delivery of its catalytic domain to the cell interior.
authors.affiliation: Department of Medicine, University of Virginia School of Medicine, Charlottesville 22908.
authors.forename: E L
authors.initials: EL
authors.lastname: Hewlett
authors.forename: L
authors.initials: L
authors.lastname: Gray
authors.forename: M
authors.initials: M
authors.lastname: Allietta
authors.forename: I
authors.initials: I
authors.lastname: Ehrmann
authors.forename: V M
authors.initials: VM
authors.lastname: Gordon
authors.forename: M C
authors.initials: MC
authors.lastname: Gray
mesh_terms: D037361:Adenylate Cyclase Toxin; D000494:Allosteric Regulation; D001886:Bordetella pertussis / Q000378:metabolism*; D002118:Calcium / Q000502:physiology*; D005453:Fluorescence; D008854:Microscopy, Electron; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014357:Trypsin; D010566:Virulence Factors, Bordetella / Q000737:chemistry / Q000378:metabolism*
chemical_list: D037361:Adenylate Cyclase Toxin; D010566:Virulence Factors, Bordetella; D014357:Trypsin; D002118:Calcium