Refined structure of orthorhombic lysozyme crystallized at high temperature: correlation between morphology and intermolecular contacts

The structure of orthorhombic hen egg-white lysozyme (HEWL) crystallized at 310 K has been refined at 1.7 Angstrom resolution. Large displacements of the side-chain atoms with respect to the tetragonal structure were observed in many places, in contrast to small displacements of the main-chain atoms . A chloride-ion binding site was observed at an interface of two molecules , but at a different position to the binding site in the tetragonal form. T he analysis of intermolecular contacts in the crystal has shown the presenc e of three independent intermolecular contacts which are called macrobonds A, B and C. Arginine side chains are frequently involved in these macrobond s, suggesting that the high frequency of this residue in HEWL may be a poss ible reason for the multiple polymorphs of this protein. The crystal forms were determined using a light-reflecting device on a four-circle diffractom eter. Correlations between crystal forms and the three-dimensional macrobon d networks were interpreted in terms of their components in various crystal lographic planes, making use of approximate strengths of hydrogen-bond and van der Waals interatomic forces.