Pande, K. et al. Proc. Natl. Acad. Sci. USA 115, 11772–11777 (2018).

In traditional solution-scattering experiments conducted at synchrotrons, the X-ray exposure time is longer than the time required for a particle to undergo a full rotation. In fluctuation X-ray scattering (FXS), solution scattering data are collected at time scales below particle rotational diffusion times, which means that much more information can be extracted from an experiment. Though proposed decades ago, this type of experiment has only now been made possible with the advent of X-ray free-electron laser (XFEL) technology, which provides high-intensity, femtosecond-length X-ray pulses, enabling the rapid capture of snapshots of thousands of individual particles. Pande et al. applied FXS to determine a nanometer-resolution structure of the giant Paramecium bursaria Chlorella virus. Their reconstruction indicates that the viral capsid has icosahedral symmetry, whereas the interior of the virus is disordered. FXS could potentially be applied in a time-resolved manner to obtain insights into structural dynamics.