Calcium-independent calmodulin binding and two-metal-ion catalytic mechanism of anthrax edema factor.
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.
Shen
Yuequan
Y
Ben-May Institute for Cancer Research, The University of Chicago, Chicago, IL 60637, USA.
Zhukovskaya
Natalia L
NL
Guo
Qing
Q
Florián
Jan
J
Tang
Wei-Jen
WJ
D037361:Adenylate Cyclase Toxin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000942:Antigens, Bacterial; D001408:Bacillus anthracis / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D018360:Crystallography, X-Ray; D005098:Exotoxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005964:Glucosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000737:chemistry; D008670:Metals / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D037361:Adenylate Cyclase Toxin; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002147:Calmodulin; D005098:Exotoxins; D008670:Metals; D046912:Multiprotein Complexes; D011994:Recombinant Proteins; C030325:anthrax toxin; D006639:Histidine; C111504:ExoY protein, bacteria; D005964:Glucosyltransferases; D000262:Adenylyl Cyclases; D002118:Calcium
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