Calcium-independent calmodulin binding and two-metal-ion catalytic mechanism of anthrax edema factorShen, Y., Zhukovskaya, N.L., Guo, Q., Tang, W.-J.
(2005) EMBO J 24: 929-941
- PubMed: 15719022
- DOI: https://doi.org/10.1038/sj.emboj.7600574
- Primary Citation of Related Structures:
1XFU, 1XFV, 1XFW, 1XFX, 1XFY, 1XFZ, 1Y0V
- PubMed 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.
Ben-May Institute for Cancer Research, The University of Chicago, Chicago, IL 60637, USA.