Cost-benefit analysis of cryogenic electron tomography subtomogram averaging of chaperonin MmCpn at near atomic resolution.

Abstract

Cryogenic electron microscopy single particle reconstruction (cryoEM-SPR) has evolved into a routine approach for determining macromolecule structures to near-atomic resolution. Cryogenic electron tomography subtomogram averaging (cryoET-STA) towards similar resolution, in contrast, is still under active development. CryoET can capture the 3D snapshot of individual macromolecules by stage tilting, offering multiple angular views per particle than the single particle reconstruction approach. Here we use the archaea chaperonin MmCpn as a model macromolecule to investigate the resolution limiting factors of cryoET-STA in terms of cumulative electron dose, ice thickness, subtomogram numbers and tilt angle ranges. By quantitative analysis of these factors against the STA reconstruction resolution, we delineate the feasibility of attaining high resolution structure determination with cryoET-STA. This study provides biophysical guidance for the application of cryoET-STA towards high resolution and the cost against benefit of using cryoET-STA to achieve an efficient outcome at the desired resolution.