Crystal structure of the programmed cell death 5 protein from Sulfolobus solfataricus.

Programmed cell death 5 (PDCD5) is a vital signaling protein in the apoptosis pathway in eukaryotes. It is known that there are two dissociated N-terminal regions and a triple-helix core in eukaryotic PDCD5. Structural and functional studies of PDCD5 from hyperthermophilic archaea have been limited to date. Here, the PDCD5 homolog Sso0352 (SsoPDCD5) was identified in Sulfolobus solfataricus, the SsoPDCD5 protein was expressed and crystallized, and the phase was identified by single-wavelength anomalous diffraction. The native SsoPDCD5 crystal belonged to space group C2 and diffracted to 1.49 Å resolution. This is the first crystal structure of a PDCD5 homolog to be solved. SsoPDCD5 shares a similar triple-helix bundle with eukaryotic PDCD5 but has a long α-helix in the N-terminus. A structural search and biochemical data suggest that SsoPDCD5 may function as a DNA-binding protein.