Platinum-induced space-group transformation in crystals of the platelet glycoprotein Ibα N-terminal domain

The interaction between platelet glycoprotein (GP) Ibα and von Willebrand factor (VWF) is essential for thrombus formation, leading to the arrest of bleeding. The N-terminal domain of GP Ibα, which contains the binding sites for VWF and α-thrombin, crystallized in the tetragonal space group P4₃ with one molecule in the asymmetric unit. When the crystals were treated with platinum, the crystals changed their symmetry from tetragonal to monoclinic P2₁ with two molecules in the asymmetric unit. The structure of the monoclinic form was solved using two-wavelength platinum anomalous dispersion data. The tetragonal crystal structure was subsequently solved using molecular-replacement tech­niques using the monoclinic structure as the search model and was refined with 1.7 Å resolution data.