Abstract
Protein crystal growth reflects intermolecular interactions under hydration effects. Experimental and theoretical approaches to the stable face, polymorphs, and humidity-induced phase transitions are introduced. The first example is cubic insulin. We determined the stable crystal form and carried out in situ observation on surfaces by an optical microscope. In order to understand the stable form, intermolecular interactions were evaluated by the macrobond and the electrostatic energy transfer (EET) analyses. Although there are some difficulties in treatment of hydration effects, the calculated surface energy explains the stable form. The second example is polymorphs of ribonuclease A. Relationship between intermolecular interactions and crystallization conditions was discussed on the basis of polarity of contact surfaces. The last example is thaumatin, where decrement of water content induces crystal structural transformation. The decrease in water leads to a rise in salt concentration in the crystal, and, as a result, molecules might move to increase nonpolar contact area.
