The structure of the signal receiver domain of the Arabidopsis thaliana ethylene receptor ETR1.

Abstract Background: In Arabidopsis thaliana , ethylene perception and signal transduction into the cell are carried out by a family of membrane-bound receptors, one of which is ethylene resistant 1 (ETR1). The large cytoplasmic domain of the receptor showed significant sequence homology to the proteins of a common bacterial regulatory pathway, the two-component system. This system consists of a transmitter histidine kinase and a response regulator (or signal receiver). We present the crystal structures of the first plant receiver domain ETR RD (residues 604–738) of ETR1 in two conformations. Results: The monomeric form of ETR RD resembles the known structure of the bacterial receiver domain. ETR RD forms a homodimer in solution and in the crystal, an interaction that has not been described previously. Dimerization is mediated by the C terminus, which forms an extended β sheet with the dimer-related β -strand core. Furthermore, the loop immediately following the active site adopts an exceptional conformation. Conclusions: The three-dimensional structure of ETR RD shows the expected conformational conservation to prokaryotic receiver proteins, such as CheY and CheB, both of which are part of the chemotaxis signaling pathway. ETR RD provides the first detailed example of a dimerized receiver domain. Given that the dimer interface of ETR RD coincides with the phosphorylation-dependent interfaces of CheY and CheB, we suggest that the monomerization of ETR RD is phosphorylation-dependent too. In the Mg 2+ -free form of ETR RD , the γ -loop conformation does not allow a comparable interaction as observed in the active-site architectures of Mg 2+ -bound CheY from Escherichia coli and Salmonella typhimurium .