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 Ca(2+). 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 P3(1)21 (or P3(2)21) with cell dimensions a = b = 79.8, c = 57.08 A, alpha = beta = 90.0 and gamma, = 120.0 degrees diffracted to 2.8 A. The second crystal form diffracts to 1.8 A and belongs to monoclinic space group P2(1) with cell dimensions a = 50.1, b = 79.7, c = 57.1 A and beta = 91.2 degrees.