High resolution in situ structural determination of heterogeneous specimen

Abstract

Macromolecular complexes are intrinsically flexible and often challenging to purify for structure determination by single particle cryoEM. Such complexes may be studied in situ using cryo-electron tomography combined with sub-tomogram alignment and classification, which in exceptional cases reaches sub-nanometer resolution, yielding insight into structure-function relationships. All maps currently deposited in the EMDB with resolution < 9 [A] are from macromolecules that form ordered structural arrays, like viral capsids, which greatly simplifies structural determination. Extending this approach to more common specimens that exhibit conformational or compositional heterogeneity, and may be available in limited numbers, remains challenging. We developed emClarity, a GPU-accelerated image processing package, specifically to address fundamental hurdles to this aim, and demonstrate significant improvements in the resolution of maps compared to those generated using current state-of-the-art software. Furthermore, we devise a novel approach to sub-tomogram classification that reveals functional states not previously observed with the same data.\n\nThe software is freely available from https://www.github.com/bHimes/emClarity\n\nTutorial documentation and videos at https://www.github.com/bHimes/emClarity/wiki