Crystallization and preliminary X-ray crystallographic analysis of Ca2+-independent and Ca2+-dependent species of the type II antifreeze protein.

Ca2+-independent and Ca2+-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 Ca2+-independent species from Brachyosis rostratus belongs to space group P2(1)2(1)2(1), with unit-cell parameters a = 43.3, b = 48.4, c = 59.7 A, and diffraction data were collected to 1.34 A resolution. For the Ca2+-dependent type II AFP species from Hypomesus nipponensis, crystallization was carried out for its Ca2+-free and Ca2+-bound states. 1.25 A resolution data were collected from the crystal in the Ca(2+)-free state, which exhibited P3(1)21 (or P3(2)21) symmetry, with unit-cell parameters a = b = 66.0, c = 50.3 A. Data collection could be extended to 1.06 A resolution for the crystal in the Ca2+ -bound state, which appeared to be isomorphous to the crystal in the Ca2+-free state (unit-cell parameters a = b = 66.0, c = 49.8 A). These data will allow us to determine the high-resolution structures of the two species of type II AFP.