Crystal Pathologies

Abstract

Truly ideal crystals are rarely realized in macromolecular crystallography. The conformational complexity of protein molecules and the promiscuity of their chance interactions often conspire to give crystals in which the molecules are present in alternative configurations. When the alternative configurations occur randomly throughout the crystal, one is faced by a case of static disorder (often indistinguishable from thermal motion), leading to limited resolution and potential challenges in modeling the underlying structural variations. Despite those challenges, the case of random disorder is arguably the simplest to understand and interpret. A variety of more complex categories of crystal disorder occur when alternative molecular configurations, orientations, or positions are not random, but correlated to each other in one way or another throughout the crystal specimen.