Highlights
- Recent cryo-EM technology allows near-atomic structural resolution of many complexes.
- Conformational changes, functionally relevant, hinder higher resolution of complexes.
- Most image processing procedures do not consider continuous conformational changes.
- New methods are needed to observe details of the change cycle directly from images.
- This review will help the future computational developments in cryo-EM.
Thanks to latest technical advances in cryo-electron microscopy (cryo-EM), structures of macromolecular complexes (viruses, ribosomes, etc.) are now often obtained at near-atomic resolution. Also, studies of conformational changes of complexes, in connection with their function, are gaining ground. Conformational variability analysis is usually done by classifying images in a number of discrete classes supposedly representing all conformational states present in the specimen. However, discrete classes cannot be meaningfully defined when the conformational change is continuous (the specimen contains a continuum of states instead of a few discrete states). For such cases, first image analysis methods that explicitly consider continuous conformational changes were recently developed. The latest developments in cryo-EM image analysis methods for conformational variability analysis are the focus of this review.