Purification, crystallization and preliminary X-ray diffraction studies of recombinant calcium-binding domain of the small subunit of porcine calpain

The calcium-binding domain of the small subunit of porcine calpain (domain VI) has been expressed in Escherichia coli, purified, and crystallized in the presence of Ca²⁺. Two crystal forms have been obtained by the vapor-diffusion method using PEG 6000 as the precipitant. Crystal form I, belonging to trigonal space group P3₁21 (or P3₂21) with cell dimensions a = b = 79.8, c = 57.08 Å, α = β = 90.0 and γ, = 120.0° diffracted to 2.8 Å. The second crystal form diffracts to 1.8 Å and belongs to monoclinic space group P2₁ with cell dimensions a = 50.1, b = 79.7, c = 57.1 Å and β = 91.2°.