Calcium dependence of the interaction between calmodulin and anthrax edema factor.
Edema factor (EF), a toxin from Bacillus anthracis (anthrax), possesses adenylyl cyclase activity and requires the ubiquitous Ca2+-sensor calmodulin (CaM) for activity. CaM can exist in three major structural states: an apo state with no Ca2+ bound, a two Ca2+ state with its C-terminal domain Ca2+-loaded, and a four Ca2+ state in which the lower Ca2+ affinity N-terminal domain is also ligated. Here, the interaction of EF with the three Ca2+ states of CaM has been examined by NMR spectroscopy and changes in the Ca2+ affinity of CaM in the presence of EF have been determined by flow dialysis. Backbone chemical shift perturbations of CaM show that EF interacts weakly with the N-terminal domain of apoCaM. The C-terminal CaM domain only engages in the interaction upon Ca2+ ligation, rendering the overall interaction much tighter. In the presence of EF, the C-terminal domain binds Ca2+ with higher affinity, but loses binding cooperativity, whereas the N-terminal domain exhibits strongly reduced Ca2+ affinity. As judged by chemical shift differences, the N-terminal CaM domain remains bound to EF upon subsequent Ca2+ ligation. This Ca2+ dependence of the EF-CaM interaction differs from that observed for most other CaM targets, which normally interact only with the Ca2+-bound CaM domains and become active following the transition to the four Ca2+ state.
Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
Tobias S
TS
Ulmer
Sandriyana
S
Soelaiman
Shipeng
S
Li
Claude B
CB
Klee
Wei-Jen
WJ
Tang
Ad
A
Bax
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000942:Antigens, Bacterial; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001408:Bacillus anthracis / Q000737:chemistry; D001427:Bacterial Toxins; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism*; D004347:Drug Interactions; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D010446:Peptide Fragments / Q000378:metabolism
D000942:Antigens, Bacterial; D001059:Apoproteins; D001427:Bacterial Toxins; D002147:Calmodulin; D010446:Peptide Fragments; C030325:anthrax toxin; D000262:Adenylyl Cyclases; D002118:Calcium