Crystallization and preliminary X‐ray analysis of pseudo‐merohedrally twinned crystals of the full‐length β 2 subunit of the Kv1 K + channel from Rattus norvegicus

The eukaryotic Kv1 voltage‐gated K + channel is composed of four α subunits and four β subunits. The full‐length β 2 subunit from Rattus norvegicus has been expressed in Esherichia coli , purified and then crystallized. A careful molecular‐replacement study using the structure of the truncated β 2 subunit reveals that the crystals are perfectly pseudo‐merohedrally twinned. While the apparent space group of the crystals was P 42 1 2, the real space group was shown to be P 2 1 2 1 2, with unit‐cell parameters a = 222.6, b = 222.6, c = 82.3 Å. An asymmetric unit of the crystal contains two β 2 tetramers (MW = 340 kDa). A data set was collected from a crystal to 2.0 Å resolution, with 266 659 independent observations (93.0% complete) and R merge = 0.06. Although the crystals are perfectly twinned, they are still suitable for structural determination by molecular replacement using the truncated β 2 ‐subunit structure.