Preliminary crystallographic analysis of the ankyrin-repeat domain of Arabidopsis thaliana AKT1: identification of the domain boundaries for protein crystallization

The Arabidopsis thaliana K+ transporter 1 (AKT1) participates in the maintenance of an adequate cell potassium (K+) concentration. The CBL-interacting protein kinase 23 (CIPK23) activates AKT1 for K+ uptake under low-K+ conditions. This process is mediated by the interaction between the cytosolic ankyrin-repeat (AR) domain of AKT1 and the kinase domain of CIPK23. However, the precise boundaries of the AR domain and the residues responsible for the interaction are still unknown. Here, the optimization procedure to obtain an AR domain construct suitable for crystallization and the preliminary crystallographic analysis of the obtained crystals are reported. The crystals belonged to space group P2(1)2(1)2, with unit-cell parameters a = 34.83, b = 65.89, c = 85.44 angstrom, and diffracted to 1.98 angstrom resolution.