Mechanism of crystal growth of protein: Differential scanning calorimetry of thermolysin crystal suspension

Mechanism of crystal growth of thermolysin was investigated through a thermal measurement by differential scanning calorimetry (DSC) of a crystal suspension which is under the progress of crystallization. The DSC curve obtained for the crystal suspension indicates that there are at least three groups of thermolysin differing in the thermal stability. The presence of the three groups is consistent with the two step mechanism of crystal growth of thermolysin previously proposed: the crystallization of thermolysin proceeds through two steps; the first step is the formation of primary particles with 20 nm in diameter; and the second step is the crystal growth by highly ordered aggregation of the primary particles. In the DSC curve, Peak 1 (the denaturation temperature: 74.5-75.0 degrees C), Peak 2 (85.5-87.0 degrees C) and Peak 3 (95.5 degrees C) are assigned to the denaturation of monomers, primary particles (oligomers), and crystals, respectively.