CRYSTALLIZATION AND MOLECULAR PACKING ANALYSIS OF BARSTAR CRYSTALS

Barstar, the natural inhibitor of barnase crystallizes in many differe nt crystal forms under almost identical conditions. Although barstar i s a monomeric protein, it crystallizes with four molecules in the asym metric unit in two crystal forms, rhombohedral (space group R3; a = b = 118.0 Angstrom; c = 75.5 Angstrom) and tetragonal (space group P4; a = b = 105.1 Angstrom; c = 36.0 A), which exist simultaneously under i dentical crystallization conditions. The relation between the four mol ecules in the asymmetric unit of the crystals belonging to space group P4 can be interpreted in terms of a small distortion in the crystallo graphic symmetry of the higher symmetry space group P422.