Two different crystal forms of sorcin, a penta-EF-hand Ca²⁺-binding protein

Sorcin is a 198 amino-acid Ca²⁺-binding protein that belongs to the penta-EF-hand family. Its Ca²⁺-binding domain (residues 33–198) has been crystallized in the absence of Ca²⁺ in two different crystal forms. Two complete data sets have been collected on a synchrotron source under cryocooling conditions from crystals grown using ammonium sulfate as precipitant: monoclinic crystals in space group C2, with unit-cell parameters a = 130.93, b = 103.85, c = 78.55 Å, β = 118.0°, diffracting to 2.1 Å, and tetragonal crystals in space group P42₁2, with unit-cell parameters a = b = 103.33, c = 79.15, diffracting to 2.7 Å. Crystals were also grown using PEG 6000 as precipitating agent. They also belong to space group C2, diffract to 2.8 Å and their unit-cell parameters are very similar to the first form. Structure determination by molecular replacement has been initiated. Structural information should be useful for elucidating the interaction of sorcin with membrane targets.