The three-dimensional (3D) structures of molecules are very important for us
to study the functions of molecules in many applications. Although the structures
of most existing proteins are solved by x-ray crystallography or NMR spectroscopy,
they do not give the \"full picture\" of a functional biological complex. The study of
large macromolecular complexes, such as viruses, ion channels, the ribosome and other
machines of various types, offers a more complete structural and functional description
of the protein machinery. However, it becomes much more difficult for us to crystallize
such large macromolecular complexes. Therefore, the non-crystallography technique using
cryo-electron microscopy (CryoEM), commonly known as Single Particle Reconstruction,
provides a powerful tool in revealing the structures of large complexes at sub-nanometer
resolutions (5 - 10 A). Coupled with this technique are many algorithms newly developed
in Image Processing, which are the main goal of our research in this project.
The following figure shows the overall procedure of this technique, starting from the two
dimensional Cryo-EM images and/or the Protein Data Bank and ending up with the three
dimensional pseudo-atomic structures of the large macromolecular complexes.