Shape change in crystallization of biological macromolecules

Conformational changes, and the formation of densely packed ordered aggregates or crystals, are behaviors that profoundly affect the properties of a molecule. Using the example of biological macromolecules, we discuss two types of interactions between these two behaviors. First, we demonstrate that shape change may be driven by crystallization if the gain in crystallization free energy is sufficient to overcome the transition to an unfavorable molecular conformation. Hence, the crystal structures of flexible molecules may be a poor representation of their free-phase atomic arrangements. Second, molecules with conformational variability, such as proteins, may facilitate the nucleation of their crystals by forming dense liquid clusters enriched in domain-swapped or misassembled oligomers. In the clusters, the nucleation barrier is reduced due to the lower surface free energy of the crystal/dense liquid interface, and nucleation is significantly faster.