“Combining tomograms of homogeneous particles in order to improve resolution, reduce noise, and remove the missing wedge effect: Sulfolobus Turreted Icosahedral Virus”

“Combining tomograms of homogeneous particles in order to improve resolution, reduce noise, and remove the missing wedge effect: Sulfolobus Turreted Icosahedral Virus”

Peter C Doerschuk -Biomedical Engineering Electrical and Computer Engineering Cornell University, Ithaca, NY

Electron computed tomography (ECT) of viruses provides 3-D structures that intrinsically show any asymmetry that is present in the particle.  Furthermore, if done in situ on infected cells rather than in vitro on purified particles, ECT shows the virus in is natural state without any artifacts due to purification.  However, the 3-D structures are of poorer quality than current single-particle cryo EM structures in terms of resolution, noise, and the presence of a missing wedge of data in reciprocal space due to the data collection process.  For objects where one or more tomograms show multiple instances of the object, we have developed methods which classify each object and jointly reconstruct each class of object from the tomograms not from the raw images.  Applying these methods to Sulfolobus Turreted Icosahedral Virus clearly shows two classes of particle, a mature virion and a procapsid without a genome core, and demonstrates that genome packaging does not cause a dramatic rearrangement of the capsid.  This work is in collaboration with Kang Wang (Cornell University) and Chi-yu Fu and John E. Johnson (both The Scripps Research Institute).