Abstract

Complementary to the structure determination by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy, three-dimensional (3D) reconstruction from cryo-electron microscopic (cryoEM) images has become one of the major methods in structural biology (Frank 2002; Frank et al. 2002). It does not require large quantities of materials to start experiments, nor is high-quality crystalline arrangement of the target molecules a must. For some high-symmetry objects, 3D reconstructions at atomic resolutions have been achieved when high-quality specimens were imaged under more advanced microscopes (Yu et al. 2008; Zhang et al. 2008b, 2013; Zhou 2008, 2011). For a majority of the biological specimens, cryoEM analysis at the current state of the art is only able to deliver lowto intermediate-resolution structures, which are insufficient for the ab initio building of atomic models. Nevertheless, it does provide a venue to study the dynamics of biological complexes as well as the component organization of the target macromolecules in cells or even tissues (Frank 2002). For the study of some multidomain ion channels, the combination of all three structural techniques may be necessary in order to address the fundamental questions regarding the functional properties of these channels.