INTERNAL SYMMETRY OF THE MOLECULAR CHAPERONE CPN60 (GROEL) DETERMINEDBY X-RAY CRYSTALLOGRAPHY

The Escherichia coli molecular chaperone cpn60 oligomer, [cpn60]14, al so called GroEL, has been crystallized and examined by X-ray crystallo graphy and self-rotation function calculations. The crystals show unit -cell dimensions a = 143.3, b = 154.6 and c = 265 angstrom, with alpha = 82, beta = 95 and gamma = 107-degrees. The space group is P1 and cr ystals diffract to 7 angstrom. X-ray analysis shows that the oligomer has one sevenfold symmetry axis and seven twofold axes that are all pe rpendicular to the sevenfold. The symmetry suggests that [cpn60]24 con sists of two heptamers, [cpn60]7, Stacked on top of each other. The or ientations of the symmetry axes of the two independent [cpn60]14 oligo mers in the triclinic unit cell have been determined relative to the c rystallographic axes. The two oligomers in the unit cell are arranged side-by-side, but the second oligomer is rotated 26-degrees around the sevenfold axis relative to the first oligomer.