Open AccessMeasurement of atom resolvability in cryo-EM maps with Q-scores
Author(s) -
Grigore Pintilie,
Kaiming Zhang,
Zhaoming Su,
Shanshan Li,
Michael F. Schmid,
Wah Chiu
Publication year - 2020
Publication title -
nature methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 19.469
H-Index - 318
eISSN - 1548-7105
pISSN - 1548-7091
DOI - 10.1038/s41592-020-0731-1
Subject(s) - cryo electron microscopy , resolution (logic) , macromolecule , scale (ratio) , ion , atom (system on chip) , physics , statistical physics , crystallography , computer science , chemistry , artificial intelligence , nuclear magnetic resonance , biochemistry , quantum mechanics , embedded system
Cryogenic electron microscopy (cryo-EM) maps are now at the point where resolvability of individual atoms can be achieved. However, resolvability is not necessarily uniform throughout the map. We introduce a quantitative parameter to characterize the resolvability of individual atoms in cryo-EM maps, the map Q-score. Q-scores can be calculated for atoms in proteins, nucleic acids, water, ligands and other solvent atoms, using models fitted to or derived from cryo-EM maps. Q-scores can also be averaged to represent larger features such as entire residues and nucleotides. Averaged over entire models, Q-scores correlate very well with the estimated resolution of cryo-EM maps for both protein and RNA. Assuming the models they are calculated from are well fitted to the map, Q-scores can be used as a measure of resolvability in cryo-EM maps at various scales, from entire macromolecules down to individual atoms. Q-score analysis of multiple cryo-EM maps of the same proteins derived from different laboratories confirms the reproducibility of structural features from side chains down to water and ion atoms.