Cryoelectron microscopy of macromolecular complexes

Although there are many macromolecular complexes which play extremely important roles in biology, and despite continued progress in X-ray crystallographic and NMR methods, it is still very difficult to obtain atomic level structural information about such large assemblies. It is now clear that a powerful approach is to combine structural information obtained at different levels. Cryoelectron microscopy of frozen-hydrated samples together with computer based 3-D reconstruction can give structural information at the quaternary level. This can then be combined with atomic level structures of individual components, obtained by X-ray crystallography or NMR to build-up a detailed picture of the overall architecture of the complexes and of the interactions between the components. In our laboratory we are particularly interested in developing the complementarity between the different structural approaches. The aim of this short review is to briefly present our ongoing work using cryoelectron microscopy of vitreous ice-embedded samples as a quantitative tool to investigate the assembly and organization of two important biological structures, namely, microtubules and viruses, in particular the bluetongue virus.