The structure of a centrosymmetric protein crystal.

Crystals of racemic rubredoxin, prepared by independent chemical synthesis of the two enantiomers, have been grown and characterized. The unit cell contains two molecules, one of each enantiomer. Examination of the intensity distribution in the diffraction pattern revealed that the crystals are centrosymmetric. This was confirmed by solution of the structure to 2 A resolution via molecular replacement methods. The electron density maps are of very high quality due to the fact that the phase of each reflection must be exactly 0 degrees or exactly 180 degrees. These results demonstrate the feasibility of using synthetic racemic proteins to yield centrosymmetric protein crystals with electron density maps that have very low phase error and model bias.