Forum 11/06/2008

“Dissection of Cryo-EM image reconstructions”

Reza Khayat, Ph.D. – Research Associate, Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA

Cryo electron microscopy (cryo-EM) is a powerful technique for visualizing and studying large macromolecular complexes.  However, the image reconstructions produced by EM can at times be daunting to interpret -due to the high degree of information they contain.  An obvious solution to this dilemma would be to use a divide-and-conquer approach.  This would involve the incorporation of crystal and NMR structures, and homology models into the EM image reconstruction to generate a pseudo-atomic model of the macromolecular complex.  The merger of these fields can be particularly powerful when the complex in study is composed of a heterogeneous mixture of components, such that the location of each component can be identified using its respective atomic structure.  In cases where not all atomic structures are available, difference maps could be employed to identify the location of the components.  Moreover, structural and biochemical information regarding the dynamic behavior of the complex can be obtained using these methods.  In this talk I will provide two examples where cryo-EM in conjunction with x-ray crystallography have helped identify the dynamic behavior of two icosahedral viruses (Flock House Virus and Sulfolobus Turreted Icosahedral Virus) that are crucial for the infectivity of these viruses.  I will also discuss certain parameters that must be observed in order to obtain a reliable difference map.

Leave a Reply