Post-acquisition super resolution for cryo-electron microscopy

Abstract

Super resolution detector acquisition for cryo-EM has been used to improve the clarity of cryo-EM reconstructions. Recent reports have demonstrated achieving resolutions beyond the physical Nyquist limit using super resolution acquisition. Here, we demonstrate exceeding the physical Nyquist limitation by pre-processing the raw micrograph movies from "counting mode" data which has already reached physical Nyquist reconstruction resolution. To demonstrate functionality, micrograph movies of five datasets were pre-processed and demonstrate that it is possible to exceed the physical Nyquist limit via pixel doubling before motion correction. We call this "post-acquisition super resolution", or PASR. While this was originally developed for processing of giant virus datasets, where acquiring at high magnification is not always possible or desirable, it is also shown to work for smaller objects such as adeno-associated virus (AAV) and apoferritin, both of which are still high symmetry, and jack bean urease, with lower symmetry. PASR could reduce the magnification required to achieve desired resolutions, which may increase collection efficiency. PASR can also be of use for in vivo tomography and facilities with high storage demands. However, this method should only be used for data which is able to achieve the Nyquist limit without PASR pre-processing. It will not improve attained resolutions of data which does not already reach the Nyquist limit.