CRYSTALLIZATION AND PRELIMINARY-X-RAY DIFFRACTION CHARACTERIZATION OFA DIMERIZING FRAGMENT OF THE ROD DOMAIN OF THE DICTYOSTELIUM GELATIONFACTOR (ABP-120)

We have expressed in Escherichia coli a construct corresponding to seq uence repeats 5 and 6 of the rod domain of the actin-binding protein D ictyostelium gelation factor (ABP-120), We have obtained orthorhombic P2(1)2(1)2(1) crystals of the protein with a = 43.5 Angstrom, b = 103. 2 Angstrom, c = 124.4 Angstrom. These crystals diffract past 2.2 Angst rom resolution using synchrotron radiation and are suitable for high-r esolution structural analysis. ABP-120 is a key component of the Dicty ostelium cytoskeleton, where it functions to crosslink. F-actin filame nts into networks, This crosslinking function of ABP-120 depends cruci ally on the formation of dimeric molecules that contain an actin-bindi ng site on each chain, and this dimerization is brought about through interactions between repeating sequence modules in the rod domain, Bec ause the construct we have expressed retains the ability to dimerize, it should enable us to establish the precise manner in which these seq uence repeats interact with one another in the intact molecule. (C) 19 97 Academic Press.