Crystallization and preliminary X-ray diffraction analysis of the 190- Å-long coiled-coil dimerization domain of the actin-bundling protein cortexillin I from Dictyostelium discoideum

We have crystallized the ~ 190-Å-long parallel twostranded coiled- coil oligomerization domain of the actin-bundling protein cortexillin I from Dictyostelium discoideum. The orthorhombic crystals belong to the space group C2221 with unit cell dimensions of a = 71.3 Å, b = 127.8 Å, and c = 91.6 Å. As both native and selenomethionine-substituted protein crystals diffract to 3.0 and 2.85 Å resolution, respectively, using synchrotron radiation, they are suitable for the first high-resolution structural analysis of a two- stranded coiled coil comprising more than six heptad repeats. Moreover, because the polypeptide chain fragment contains a recently identified two- heptad-repeat long sequence that is indispensable for the assembly of the cortexillin I coiled-coil oligomerization domain, its high-resolution structure should enable us to extend our knowledge on the molecular mechanisms underlaying coiled-coil formation and to establish the precise manner in which the two 'trigger' sequences interact with one another in the dimer.