Pushing the resolution limits in cryo electron tomography of biological structures

Cryo electron tomography is a three-dimensional imaging technique that is suitable for imaging snapshots of the structural arrangements of biomolecular complexes and macromolecules, both in vitro and in the context of the cell. In terms of attainable resolution, cryo electron tomographic reconstructions now show resolvable details in the 5-10 nm range, connecting optical microscopy with molecular imaging techniques. In view of the current developments in super-resolution light microscopy and correlative light and electron microscopy, cryo electron tomography will be increasingly important in structural biology as a tool to bridge light microscopy with molecular imaging techniques like NMR, X-ray diffraction and single particle electron microscopy. In cell biology, one goal, often referred to as visual proteomics, is the molecular mapping of whole cells. To achieve this goal and link cryo electron tomography to these high-resolution techniques, increasing the attainable resolution to 2-5 nm is vital. Here, we provide an overview of technical factors that limit the resolution in cryo electron tomography and discuss how during data acquisition and image processing these can be optimized to attain the highest possible resolution. Also, existing resolution measurement approaches and current technological developments that potentially increase the resolution in cryo electron tomography are discussed.