4/19/2023 0 Comments Atomic modelIn this paper, we present a measure (FSC- Q) for local quality estimation of the fit of the atomic model to the Coulomb potential map. Local map-to-model fit measurements have been introduced, such as EMRinger 9, which takes into account density values near carbon-ß atom, and the recent Q-score 10, which measures the correlation between the map values at points around the atom and a reference Gaussian-like function. However, these measures are based on the model itself, regardless of the cryoEM map. To evaluate the quality of an atomic model, different steric measurements have been integrated into tools, such as Molprobity 8. However, it is well known that the quality of a reconstruction depends on the local regions of the macromolecule and the resolution must therefore be calculated locally 2, 3, 4, 5, and even directionally 6, 7 (although we will not consider directional effects in this work). The agreement of a model with a map can be done in a similar way by calculating the FSC between the experimental map and a map calculated from the model. The typical resolution measure reported is based on a threshold in the Fourier shell correlation (FSC) curve between two independent reconstructions 1. The quality of the maps is usually expressed in terms of a resolution measure. Both, the quality of the reconstructed map and the derived model must be evaluated carefully to identify errors and poorly resolved regions. The next logical step is to build an atomic model that fits into the density map. In recent years, new direct detection cameras and better reconstruction algorithms yielded maps with high levels of detail. Single-particle cryo-electron microscopy (cryoEM) has become a powerful technique for the structural determination of biological macromolecules.
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