Combining structures from cryo-EM and x-ray crystallography

Abstract

Cryo-electron microscopy (cryo-EM) combined with three-dimensional image reconstruction techniques has produced structures of large macromolecular assemblies. Interpretation of low resolution (25-35 A) cryo-EM density can be greatly enhanced by mapping in crystallographic structures of component molecules. Difference imaging between the cryo-EM structure of the human adenovirus particle and a capsid calculated from the crystal structure of the major structural protein, hexon, revealed numerous minor structural components in the viral capsid. In addition, the atomic binding sites of the minor protein components were visualized on the crystallographic structure of hexon. Current studies are focused on examining the structural events during adenovirus cell entry. The receptor that triggers adenovirus internalization has been shown to be αv integrin. Cryo-EM is being used to solve the structure of adenovirus with bound Fab fragments from a monoclonal antibody that blocks binding of the virus to the receptor (Fig. 1). The antibody recognizes a linear epitope of nine amino acids that includes an Arg-Gly-Asp (RGD) integrin binding motif.