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Macromolecular refinement by model morphing using non‐atomic parameterizations
Author(s) -
Cowtan Kevin,
Agirre Jon
Publication year - 2018
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.374
H-Index - 138
ISSN - 2059-7983
DOI - 10.1107/s205979831701350x
Subject(s) - morphing , position (finance) , electron density , resolution (logic) , atomic model , convergence (economics) , statistical physics , algorithm , computer science , materials science , computational physics , electron , physics , atomic physics , artificial intelligence , quantum mechanics , finance , economics , economic growth
Refinement is a critical step in the determination of a model which explains the crystallographic observations and thus best accounts for the missing phase components. The scattering density is usually described in terms of atomic parameters; however, in macromolecular crystallography the resolution of the data is generally insufficient to determine the values of these parameters for individual atoms. Stereochemical and geometric restraints are used to provide additional information, but produce interrelationships between parameters which slow convergence, resulting in longer refinement times. An alternative approach is proposed in which parameters are not attached to atoms, but to regions of the electron‐density map. These parameters can move the density or change the local temperature factor to better explain the structure factors. Varying the size of the region which determines the parameters at a particular position in the map allows the method to be applied at different resolutions without the use of restraints. Potential applications include initial refinement of molecular‐replacement models with domain motions, and potentially the use of electron density from other sources such as electron cryo‐microscopy (cryo‐EM) as the refinement model.