Expression, purification and crystallization of a functional core of the voltage-dependent calcium channel β subunit

Two versions of the functional core of the rabbit voltage-dependent calcium channel β2a subunit were expressed in Escherichia coli. These proteins were purified to homogeneity and screened for crystallization. Crystallization conditions were refined using the hanging-drop vapour-diffusion method and two crystal forms were pursued. Crystal form I is represented by thick rods with tetragonal symmetry, unit-cell parameters a = b = 75, c = 165 Å and a diffraction limit of 3.4 Å which were obtained using ammonium sulfate as a precipitant. Crystal form II gives rise to plates with orthorhombic symmetry, unit-cell parameters a = 35, b = 75, c = 165 Å and a diffraction limit of 2.3 Å which were grown using polyethylene glycol 20K as a precipitant.