關鍵字：硫磺礦硫化葉菌、程序性細胞死亡蛋白5、X光繞射、蛋白質結晶學、DNA結合蛋白 ;Abstract The Programmed Cell Death protein 5 (PDCD5) is an important signal protein of apoptosis pathway in eukaryotes. In previous research, it is known there are triple-helix bundle and two dissociated N-terminal regions in human PDCD5 protein. However, the study of PDCD5 in hyperthermophile archaea remains unclear. Here, we identify a PDCD5 homolog from Sulfolobus solfataricus (Sso_PDCD5) and present the crystal structure of Sso_PDCD5 at a high resolution of 1.55 Å. This is the first crystal structure of a PDCD5 homolog to be solved, showing that the protein has a compact core of low flexibility with four alpha-helices at N-terminal region and a flexible unstructured C-terminal tail. The fluorescence of C-terminal tryptophan (W117) can be quenched by 20 bp double-strand DNA which indicates PDCD5 may interact with DNA by the C-terminal tail. The isothermal titration calorimety (ITC) results show C-terminal truncated protein (PDCD5_CTT, detection of K108-K118) significantly reduced the DNA-binding affinity, further demonstrated that the flexible C-terminus of Sso_PDCD5 involved in binding dsDNA. In addition, Sso_PDCD5 binds dsDNA through bridging interactions as shown in electron microscopy (EM) images. In conclusion, the structural and biochemical data suggest that Sso_PDCD5 may function as a DNA-binding protein.
Keywords: Sulfolobus solfataricus, the programmed cell death protein 5, crystal structure, X-ray crystallography, DNA-binding protein
