Crystallization and preliminary X‐ray crystallographic analysis of Ca 2+ ‐independent and Ca 2+ ‐dependent species of the type II antifreeze protein

Ca 2+ ‐independent and Ca 2+ ‐dependent species of the type II antifreeze protein (AFP) were both crystallized using the hanging‐drop vapour‐diffusion method. It appeared that the crystal of the Ca 2+ ‐independent species from Brachyosis rostratus belongs to space group P 2 1 2 1 2 1 , with unit‐cell parameters a  = 43.3, b  = 48.4, c = 59.7 Å, and diffraction data were collected to 1.34 Å resolution. For the Ca 2+ ‐dependent type II AFP species from Hypomesus nipponensis , crystallization was carried out for its Ca 2+ ‐free and Ca 2+ ‐bound states. 1.25 Å resolution data were collected from the crystal in the Ca 2+ ‐free state, which exhibited P 3 1 21 (or P 3 2 21) symmetry, with unit‐cell parameters a  =  b  = 66.0, c  = 50.3 Å. Data collection could be extended to 1.06 Å resolution for the crystal in the Ca 2+ ‐bound state, which appeared to be isomorphous to the crystal in the Ca 2+ ‐free state (unit‐cell parameters a = b = 66.0, c = 49.8 Å). These data will allow us to determine the high‐resolution structures of the two species of type II AFP.