Electron microscopy: Ultrastable gold substrates for electron cryomicroscopy.

Despite recent advances, the structures of many proteins cannot be determined by electron cryomicroscopy because the individual proteins move during irradiation. This blurs the images so that they cannot be aligned with each other to calculate a three-dimensional density. Much of this movement stems from instabilities in the carbon substrates used to support frozen samples in the microscope. Here we demonstrate a gold specimen support that nearly eliminates substrate motion during irradiation. This increases the subnanometer image contrast such that α helices of individual proteins are resolved. With this improvement, we determine the structure of apoferritin, a smooth octahedral shell of α-helical subunits that is particularly difficult to solve by electron microscopy. This advance in substrate design will enable the solution of currently intractable protein structures.