Structure determination of the constitutive 20S proteasome from bovine liver at 2.75 A resolution

The crystal structure of the 20S proteasome from bovine liver was determined by the molecular replacement method using the structure of the 20S proteasome from the yeast Sacccharomyces cerevisiae. The initial phases were refined by density modification coupled with non-crystallographic symmetry averaging. The structural model was refined with the program CNS. The final R-factor and R(free) were 0.25 and 0.29, respectively. The constitutive proteasome without any contamination by the immunoproteasome was identified in the crystal structure.