Expression, purification, crystallization and preliminary X-ray diffraction studies of human liver regucalcin

Regucalcin is a novel calcium ion (Ca²⁺) binding protein that does not contain an EF-hand motif as a Ca²⁺-binding domain and has been demonstrated to play a multi-functional role in many cell types. Human liver regucalcin, consisting of 299 amino-acid residues, was overexpressed in Escherichia coli, purified and crystallized by the vapour-diffusion method in the presence of polyethylene glycol 4000 as a precipitant. A native crystal diffracted to 2.8 Å with synchrotron radiation and belongs to space group P2₁, with unit-cell parameters a = 64.87, b = 52.52, c = 86.38 Å, β = 99.86°. Two molecules most probably exist in the asymmetric unit, corresponding to V_M = 2.2 ų Da⁻¹. Heavy-atom derivative data were collected and the Pb derivative showed one high-occupancy site per molecule.