Crystallization and preliminary X‐ray diffraction analysis of human transcobalamin, a vitamin B 12 ‐transporting protein

Transcobalamin is a cobalamin‐binding protein in mammalian plasma that facilitates the cellular uptake of vitamin B 12 . Human transcobalamin was crystallized using polyethylene glycol and ethanol as precipitants. Crystals belong to the orthorhombic space group P 2 1 2 1 2 1 , with unit‐cell parameters a = 49.04, b = 145.27, c  = 164.96 Å. A complete data set to 3.2 Å resolution was collected from a single crystal using synchrotron radiation. Estimation of the crystal packing ( V M = 3.2 Å 3  Da −1 ) and self‐rotation function analysis suggest the presence of two molecules in the asymmetric unit related by non‐crystallographic twofold symmetry.