Crystal structure of the hSac2 domain of Sac2. (A) Ribbon diagram of the overall structure of the hSac2 domain. The hSac2 domain consists of a core of two perpendicularly apposed β sheets (pink) with a C-terminal α helix (blue). (B) Ribbon diagram of the hSac2 dimer. (inset) A zoom-in view showing the four pairs of main chain hydrogen bond formed between the two β1 strands within each monomer. (C) Western blot showing Flag-Sac2 1–798 coimmunoprecipiting with GFP-Sac2 1–798 but much reduced with GFP-Sac2 1–567.