Refinement of cryo-EM structures using scattering factors of charged atoms

This paper reports a suitable treatment of electron scattering factors of charged atoms for refinement of atomic models against cryo-electron microscopy (cryo-EM) maps. The ScatCurve package developed here supports various curve models for parameterization of scattering factors and the parameter tables can be implemented in major refinement programs in structural biology. Partial charge values of charged amino acids in crystal structures were changed in small steps for refinement of the atomic models against electron diffraction data from three-dimensional crystals. By exploring a range of partial charges, the authors found the electrostatic setting that produces atomic models with improved statistics and better reflects experimental data. Structure refinement for single-particle analysis also benefits from the more accurate analysis and the programs could find wide use for model refinement against cryo-EM maps. © 2016 International Union of Crystallography.