Unraveling Polymorphism and Twisting in Near-Perfect Protein Crystals

Crystals ideally have well-formed shapes and periodic arrangements of constituent components, such as atoms and molecules. Twisting, an unconventional crystal morphology, presents itself as a puzzling and natural phenomenon. The coexistence of a continuous twisting structure and crystalline order poses a paradox. Numerous mechanisms to explain twisting have been proposed, and the elucidation of the underlying causes of spontaneous nonlong-range translational order twisting in crystals has been desired. Here, we demonstrate twisting and perfect crystals controlled by the crystal polymorphs of macromolecular crystals. We establish that the presence of either a perfectly periodic crystalline arrangement or twisting is linked to anisotropic interactions arising from salt bridges among protein molecules. Employing the dynamical theory of X-ray diffraction, we discern that twisting serves as an imperfection that cannot be attributed to conventional crystal defects within crystals. These insights suggest the origin of crystal twisting and methods for controlling crystal perfection.