Electron Crystallography of Helical Structures

Abstract Helical structures are essential for life. They connect and integrate function between distantly separated structures within a cell. Actin and microtubules are examples of helical structures that are part of the cell’s cytoskeleton and that define cell shape. They also act as the railroad tracks along which molecular motors tow subcellular material between locations within the cell. Helical structures also occur in pathological states such as the paired helical filaments associated with Alzheimer’s disease or fibers of hemoglobin in sickle cell anemia. Helical structures can serve mechanical roles; for example, the bacterial flagellar filament converts torque into thrust to propel the bacterium. In addition to naturally occurring helical structures, some molecules can be induced to form helical structures after biochemical isolation, as in the case of the nicotinic acetylcholine receptor.