Phosphorylation Alters the Interaction of the Arabidopsis Phosphotransfer Protein AHP1 with Its Sensor Kinase ETR1
In the absence of ethylene autophosphorylation of the sensor kinase ETR1 ensures low affinity of the receptor to phosphorylated HPt proteins. On the other hand, non-phosphorylated AHP1 binds to the phosphorylated ETR1 receptor with high affinity enabling phosphoryl group transfer to the HPt protein. After ethylene binding the receptor is switched to the non-phosphorylated state. This switch is accompanied by a conformational change that decreases the affinity to the phosphorylated AHP1. The transfer protein, AHP1-P is released and can move to the nucleus for further signal transfer onto response regulator proteins causing gene response. Binding of non-phosphorylated AHP1 to the activated form of the receptor is prevented by the conformational change caused in the receiver domain of the receptor by the binding of the plant hormone.