DEFECT STRUCTURE OF MACROMOLECULAR CRYSTALS

Disorder in macromolecular crystals arises from several sources. Among the most important are thermal motion and the inherent mobility of th e molecules. These cause statistical misalignment about mean lattice p oints and structural heterogeneity of the molecules. Defects in the cr ystal lattice, however, could also significantly affect the resolution and quality of diffraction data collected from some crystals. There i s a considerable diversity in the sources of defects found in crystals , such as impurity incorporation and fluctuations of growth conditions , and the defects occur in a variety of structural forms. We have used in situ atomic force microscopy to visualize examples of several of t he different classes of defects that occur in protein and virus crysta ls, ranging from unoccupied lattice sites (vacancies) to linear defect s to stacking faults. In addition, we have calculated the defect densi ty in several different macromolecular crystals and found that it vari ed in the range of 10(4)-10(6) cm(-2). Indeed, some preliminary eviden ce suggests that the ultimate resolution to which a crystal diffracts maybe a composite function of its inherent statistical disorder and it s defect structure, density, and distribution. (C) 1996 Academic Press , Inc.