Crystallization and preliminary X-ray crystallographic studies of the oligomeric death-domain complex between PIDD and RAIDD

The PIDD DD–RAIDD DD complex has been crystallized. The crystals are hexagonal and belong to space group P6₅, with unit-cell parameters a = b = 138.4, c = 207.6 Å. The crystals were obtained at room temperature; a native crystal diffracted to 3.2 Å resolution and a Hg-derivatized crystal to 4.0 Å resolution. Three large macromolecular complexes known as the death-inducing signaling complex (DISC), the apoptosome and the PIDDosome mediate caspase activation in apoptosis signaling pathways. The PIDDosome, which activates caspase-2, is composed of three protein components: PIDD, RAIDD and caspase-2. Within the PIDDosome, the interaction between PIDD and RAIDD is mediated by a homotypic interaction between their death domains (DDs). PIDD DD and RAIDD DD were overexpressed in Escherichia coli with engineered C-terminal His tags. The proteins were purified and mixed to allow complex formation. Gel-filtration and multi-angle light scattering (MALS) analyses showed that the complex is around 150 kDa in solution. The purified PIDD DD–RAIDD DD complex was crystallized at 293 K. X-ray diffraction data were collected to resolutions of 3.2 and 4.0 Å from a native and a Hg-derivative crystal, respectively. The crystals belong to space group P6₅, with unit-cell parameters a = b = 138.4, c = 207.6 Å