タンパク質結晶におけるモルフォロジーと分子間接触の相関(<小特集>バイオクリスタルにおける核形成・成長の制御機構)

抄録

The correlation between morphology and intermolecular contacts in protein crystal has been discussed by using orthorhombic hen-egg-white lysozyme as a model. In the structure of orthorhombic hen-egg-white lysozyme (HEWL) crystallized at 37℃ refined at 1.7ÅA resolution, large movements of side chain atoms compared to the tetragonal structure were observed in many places, in contrast to small movements in main chain atoms. A chloride ion binding site was observed at an interface of two molecules, but the position is different from that in the tetragonal form. The analysis of intermolecular contacts in the crystal has shown the presence of three independent intermolecular contacts which are called macrobonds A, B and C. Arginine side chains are frequently involved in these macrobonds, suggesting that the high frequency of this residue in HEWL may be a possible reason for the occurrence of multiple polymorphs of this protein. The crystal morphology was determined using a light-reflecting device on a four-circle diffractometer. The correlations between the crystal morphology and the three-dimensional networks of these macrobonds were interpreted in terms of their components in various crystallographic planes, making use of approximate strengths of hydrogen-bond and van der Waals interatomic forces. The present analysis may be generalized to any kind of protein crystals.