title: Flexible torsion-angle noncrystallographic symmetry restraints for improved macromolecular structure refinement.
abstract: One of the great challenges in refining macromolecular crystal structures is a low data-to-parameter ratio. Historically, knowledge from chemistry has been used to help to improve this ratio. When a macromolecule crystallizes with more than one copy in the asymmetric unit, the noncrystallographic symmetry relationships can be exploited to provide additional restraints when refining the working model. However, although globally similar, NCS-related chains often have local differences. To allow for local differences between NCS-related molecules, flexible torsion-based NCS restraints have been introduced, coupled with intelligent rotamer handling for protein chains, and are available in phenix.refine for refinement of models at all resolutions.
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Headd
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Echols
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Pavel V
authors.initials: PV
authors.lastname: Afonine
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Nigel W
authors.initials: NW
authors.lastname: Moriarty
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Gildea
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Adams
mesh_terms: D018360:Crystallography, X-Ray / Q000379:methods*; D006801:Humans; D046911:Macromolecular Substances / Q000737:chemistry*; D008958:Models, Molecular; D011506:Proteins / Q000737:chemistry*; D012984:Software; D014305:Triose-Phosphate Isomerase / Q000737:chemistry; D014584:User-Computer Interface
chemical_list: D046911:Macromolecular Substances; D011506:Proteins; D014305:Triose-Phosphate Isomerase
keywords: NCS; automation; macromolecular crystallography; noncrystallographic symmetry; refinement