Abstract
Edema factor (EF), a key anthrax exotoxin, has an anthrax protective antigen-binding domain (PABD) and a calmodulin (CaM)-activated adenylyl cyclase domain. Here, we report the crystal structures of CaM-bound EF, revealing the architecture of EF PABD. CaM has N- and C-terminal domains and each domain can bind two calcium ions. Calcium binding induces the conformational change of CaM from closed to open. Structures of the EF-CaM complex show how EF locks the N-terminal domain of CaM into a closed conformation regardless of its calcium-loading state. This represents a mechanism of how CaM effector alters the calcium affinity of CaM and uncouples the conformational change of CaM from calcium loading. Furthermore, structures of EF-CaM complexed with nucleotides show that EF uses two-metal-ion catalysis, a prevalent mechanism in DNA and RNA polymerases. A histidine (H351) further facilitates the catalysis of EF by activating a water to deprotonate 3'OH of ATP. Mammalian adenylyl cyclases share no structural similarity with EF and they also use two-metal-ion catalysis, suggesting the catalytic mechanism-driven convergent evolution of two structurally diverse adenylyl cyclases.
Publication types
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Comparative Study
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adenylate Cyclase Toxin / chemistry
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Adenylate Cyclase Toxin / genetics
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Adenylate Cyclase Toxin / metabolism
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Adenylyl Cyclases / chemistry*
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Adenylyl Cyclases / genetics
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Adenylyl Cyclases / metabolism*
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Amino Acid Sequence
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Antigens, Bacterial
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Bacillus anthracis / genetics
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Bacillus anthracis / metabolism
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Bacillus anthracis / pathogenicity
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Bacterial Proteins / chemistry
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Bacterial Proteins / genetics
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Bacterial Proteins / metabolism
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Bacterial Toxins
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Binding Sites
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Calcium / metabolism
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Calmodulin / chemistry
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Calmodulin / metabolism*
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Catalysis
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Crystallography, X-Ray
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Exotoxins / chemistry
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Exotoxins / genetics
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Exotoxins / metabolism
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Glucosyltransferases / chemistry
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Glucosyltransferases / genetics
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Glucosyltransferases / metabolism
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Histidine / chemistry
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Metals / metabolism
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Models, Molecular
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Molecular Sequence Data
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Multiprotein Complexes
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Recombinant Proteins / chemistry
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Sequence Homology, Amino Acid
Substances
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Adenylate Cyclase Toxin
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Antigens, Bacterial
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Bacterial Proteins
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Bacterial Toxins
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Calmodulin
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Exotoxins
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Metals
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Multiprotein Complexes
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Recombinant Proteins
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anthrax toxin
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Histidine
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ExoY protein, bacteria
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Glucosyltransferases
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Adenylyl Cyclases
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Calcium
Associated data
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PDB/1XFU
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PDB/1XFV
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PDB/1XFW
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PDB/1XFX
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PDB/1XFY
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PDB/1XFZ
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PDB/1Y0V