Mutations in the NB-ARC domain of I-2 that impair ATP hydrolysis cause autoactivation.
Publication details |
Title | Mutations in the NB-ARC domain of I-2 that impair ATP hydrolysis cause autoactivation. |
Series name | Plant physiology |
Volume | 140 |
Issue | 4 |
Year | 2006 |
Pages | 1233-45 |
Authors | Tameling, WI. Vossen, JH. Albrecht, M. Lengauer, T. Berden, JA. Haring, MA. Cornelissen, BJ. Takken, FL |
Abstract | Resistance (R) proteins in plants confer specificity to the innate immune system. Most R proteins have a centrally located NB-ARC (nucleotide-binding adaptor shared by APAF-1, R proteins, and CED-4) domain. For two tomato (Lycopersicon esculentum) R proteins, I-2 and Mi-1, we have previously shown that this domain acts as an ATPase module that can hydrolyze ATP in vitro. To investigate the role of nucleotide binding and hydrolysis for the function of I-2 in planta, specific mutations were introduced in conserved motifs of the NB-ARC domain. Two mutations resulted in autoactivating proteins that induce a pathogen-independent hypersensitive response upon expression in planta. These mutant forms of I-2 were found to be impaired in ATP hydrolysis, but not in ATP binding, suggesting that the ATP- rather than the ADP-bound state of I-2 is the active form that triggers defense signaling. In addition, upon ADP binding, the protein displayed an increased affinity for ADP suggestive of a change of conformation. Based on these data, we propose that the NB-ARC domain of I-2, and likely of related R proteins, functions as a molecular switch whose state (on/off) depends on the nucleotide bound (ATP/ADP). |
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