The structure of Arabidopsis NPR1: its function as a salicylic acid receptor and a metal-binding protein

The Arabidopsis NPR1 protein regulates systemic acquired resistance dependent on salicylic acid. Analyses by plant two-hybrid analysis in vivo and pull-down assays in vitro showed that the BTB/POZ domain of NPR1 at the N-terminus serves as an autoinhibitory domain to negate the function of the transactivation domain at the C-terminus through direct binding of these two domains. It was also shown that the binding of the BTB/POZ domain to the C-terminus of NPR1 was abolished by SA treatment, suggesting that SA could interfere directly with this binding. By gel filtration, it was demonstrated that SA affects the conformation of full-length NPR1, confirming the role of NPR1 as an SA receptor. Gel filtration analysis also indicated that NPR1 could be converted from an oligomer to a dimer with SA treatment. Furthermore, one N-terminal deletion Delta513 has been shown to act as a metal-binding protein and its two Cys-521 and Cys-529 are important for binding to Ni 2+ by pull-down assays.