Crystallization and preliminary X-ray analysis of pseudo-merohedrally twinned crystals of the full-length beta(2) subunit of the Kv1 K(+) channel from Rattus norvegicus.

The eukaryotic Kv1 voltage-gated K(+) channel is composed of four alpha subunits and four beta subunits. The full-length beta(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 beta(2) subunit reveals that the crystals are perfectly pseudo-merohedrally twinned. While the apparent space group of the crystals was P42(1)2, the real space group was shown to be P2(1)2(1)2, with unit-cell parameters a = 222.6, b = 222.6, c = 82.3 A. An asymmetric unit of the crystal contains two beta(2) tetramers (MW = 340 kDa). A data set was collected from a crystal to 2.0 A 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 beta(2)-subunit structure.