1sk6
Crystal structure of the adenylyl cyclase domain of anthrax edema factor (EF) in complex with calmodulin, 3',5' cyclic AMP (cAMP), and pyrophosphate
Structural highlights
FunctionCYAA_BACAN One of the three proteins composing the anthrax toxin, the agent which infects many mammalian species and that may cause death. EF is a calmodulin-dependent adenylyl cyclase that, when associated with PA, causes edema. EF is not toxic by itself and it is required for the survival of germinated spores within macrophages at the early stages of infection. Provokes dramatic elevation of intracellular cAMP levels in the host. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedAnthrax edema factor (EF) raises host intracellular cAMP to pathological levels through a calcium-calmodulin (CaM)-dependent adenylyl cyclase activity. Here we report the structure of EF.CaM in complex with its reaction products, cAMP and PP(i). Mutational analysis confirmed the interaction of EF with cAMP and PP(i) as depicted in the structural model. While both cAMP and PP(i) have access to solvent channels to exit independently, PP(i) is likely released first. EF can synthesize ATP from cAMP and PP(i), and the estimated rate constants of this reaction at two physiologically relevant calcium concentrations were similar to those of adenylyl cyclase activity of EF. Comparison of the conformation of adenosine in the structures of EF.CaM.cAMP.PP(i) with EF.CaM.3.dATP revealed about 160 degrees rotation in the torsion angle of N-glycosyl bond from the +anti conformation in 3.dATP to -syn in cAMP; such a rotation could serve to distinguish against substrates with the N-2 amino group of purine. The catalytic rate of EF for ITP was about 2 orders of magnitude better than that for GTP, supporting the potential role of this rotation in substrate selectivity of EF. The anomalous difference Fourier map revealed that two ytterbium ions (Yb(3+)) could bind the catalytic site of EF.CaM in the presence of cAMP and PP(i), suggesting the presence of two magnesium ions at the catalytic site of EF. We hypothesize that EF could use a "histidine and two-metal ion" hybrid mechanism to facilitate the cyclization reaction. Structural and kinetic analyses of the interaction of anthrax adenylyl cyclase toxin with reaction products cAMP and pyrophosphate.,Guo Q, Shen Y, Zhukovskaya NL, Florian J, Tang WJ J Biol Chem. 2004 Jul 9;279(28):29427-35. Epub 2004 May 6. PMID:15131111[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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