Crystallization and X-ray diffraction analysis of N-terminally truncated human ALG-2

ALG‐2 (apoptosis‐linked gene 2) is an apoptosis‐linked calcium‐binding protein with five EF‐hand motifs in the C‐terminal region. N‐terminally truncated ALG‐2 (des3‐23ALG‐2) was crystallized by the vapour‐diffusion method in buffer consisting of either 50 mM MES pH 6.5, 12.5%(v/v) 2‐propanol and 150 mM calcium acetate or 100 mM MES pH 6.0, 15%(v/v) ethanol and 200 mM zinc acetate. Crystals of the Ca2+‐bound form belonged to space group P212121, with unit‐cell parameters a = 54.8, b = 154.4, c = 237.7 Å, α = β = γ = 90°, and diffracted to 3.1 Å resolution. Crystals of the Zn2+‐bound form belonged to space group P212121, with unit‐cell parameters a = 52.8, b = 147.5, c = 230.7 Å, α = β = γ = 90°, and diffracted to 3.3 Å resolution. The structures of the Ca2+‐bound form and the Zn2+‐bound form were solved by the molecular‐replacement method. Although both crystals contained eight ALG‐2 molecules per asymmetric unit, the metal‐ion locations and octameric arrangements were found to be significantly different.