Existence of twisting in dislocation-free protein single crystals

Significance Growing high-quality protein crystals is a prerequisite for the structure analysis of proteins by X-ray diffraction. However, dislocation-free perfect protein crystals such as silicon and diamond are limited to two kinds of protein crystals. We wonder whether other high-quality or dislocation-free protein crystals still exhibit some imperfection. Here, we explore the existence of twisting as a cause of imperfection in high-quality protein crystals by X-ray topography with synchrotron radiation. The magnitude of twisting is quite small and cannot be detected by conventional techniques as optical and electron microscopy. The formation of twisting may be related to the geometric frustration mechanism proposed as a primary mechanism of twisting. This finding provides insights on high-quality protein crystals with the ubiquity of twisting.