Physical characterization of icosahedral virus ultra structure, stability, and integrity using electrospray differential mobility analysis.

We present a rapid and quantitative method to physically characterize the structure and stability of viruses. Electrospray differential mobility analysis (ES-DMA) is used to determine the size of capsomers (i.e., hexons) and complete capsids. We demonstrate how to convert the measured mobility size into the icosahedral dimensions of a virus, which for PR772 become 68.4 nm for vertex-to-vertex, 54.4 nm for facet-to-facet, and 58.2 nm for edge-to-edge lengths, in reasonable agreement with dimensions from transmission electron microscopy for other members of the family Tectiviridae (e.g., PRD1). These results indicate ES-DMA's mobility diameter most closely approximates the edge-to-edge length. Using PR772's edge length (36.0 nm) and the size of the major capsid hexon (≈8.4 nm) from ES-DMA with icosahedral geometry, PR772's T = 25 symmetry is confirmed and the number of proteins in the capsid shell is determined. We also demonstrate the use of ES-DMA to monitor the temporal disintegration of PR772, the thermal degradation of PP7, and the appearance of degradation products, essential to viral stability assays. These results lay groundwork essential for the use of ES-DMA for a variety of applications including monitoring of vaccine and gene therapy vector products, confirmation of viral inactivation, and theoretical studies of self-assembling macromolecular structures.