Crystallization and preliminary crystallographic analysis of the Escherichia coli water channel AqpZ

AqpZ is a 24 kDa integral membrane protein that facilitates water movement across the plasma membrane of Escherichia coli. In this study, the first crystallization and preliminary X-ray analysis of AqpZ are described. AqpZ was overexpressed and purified with a yield of 13 mg of purified AqpZ per litre of cell culture. The purified AqpZ was shown to be a monodisperse species consisting of tetrameric protein-detergent complexes. A crystallization condition for producing diffraction-quality crystals was identified. Initial X-ray analysis indicated that the diffraction limit of AqpZ extended to 3.6 Å. Crystals were found to belong to space groups P4₁22 or P4₃22, with unit-cell parameters a = b = 119.04, c = 380.23 Å.