Intermolecular interactions of globular proteins in the crystal state

The present work is devoted to investigation of thermal transitions in the crystals of seven proteins to compare the protein globule stability in crystal and solution. Calorimetry methods, electron and optical microscopy, as well as x-ray diffraction studies are used. It is found that protein crystals do not melt and that the destruction of the crystal lattice is a result of protein globule denaturation within the crystal. It is demonstrated that during the heating of pepsin and DF-trypsin crystals it is possible to observe phase transition of the first order. Equilibrium temperatures of protein denaturation in crystals and in solution coincide. The peculiarities of the crystal state are revealed in the increasing thermal transition cooperativity and the system relaxation period.