Mutations in the NB-ARC domain of I-2 that impair ATP hydrolysis cause autoactivation.
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).
Plant Pathology, Swammerdam Institute for Life Sciences, University of Amsterdam, 1090 GB Amsterdam, The Netherlands.
Wladimir I L
WI
Tameling
Jack H
JH
Vossen
Mario
M
Albrecht
Thomas
T
Lengauer
Jan A
JA
Berden
Michel A
MA
Haring
Ben J C
BJ
Cornelissen
Frank L W
FL
Takken
D000251:Adenosine Triphosphatases / Q000737:chemistry*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D018506:Gene Expression Regulation, Plant; D006868:Hydrolysis; D018551:Solanum lycopersicum / Q000033:anatomy & histology / Q000201:enzymology* / Q000235:genetics; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
D010940:Plant Proteins; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases