title: Modelling prior distributions of atoms for macromolecular refinement and completion.
abstract: Until modelling is complete, macromolecular structures are refined in the absence of a model for some of the atoms in the crystal. Techniques for defining positional probability distributions of atoms, and using them to model the missing part of a macromolecular crystal structure and the bulk solvent, are described. The starting information may consist of either a tentative structural model for the missing atoms or an electron-density map. During structure completion and refinement, the use of probability distributions enables the retention of low-resolution phase information while avoiding premature commitment to uncertain higher resolution features. Homographic exponential modelling is proposed as a flexible, compact and robust parametrization that proves to be superior to a traditional Fourier expansion in approximating a model protein envelope. The homographic exponential model also has potential applications to ab initio phasing of Fourier amplitudes associated with macromolecular envelopes.
authors.affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, England.
authors.forename: P
authors.initials: P
authors.lastname: Roversi
authors.forename: E
authors.initials: E
authors.lastname: Blanc
authors.forename: C
authors.initials: C
authors.lastname: Vonrhein
authors.forename: G
authors.initials: G
authors.lastname: Evans
authors.forename: G
authors.initials: G
authors.lastname: Bricogne
mesh_terms: D000818:Animals; D018360:Crystallography, X-Ray / Q000379:methods*; D007091:Image Processing, Computer-Assisted; D008962:Models, Theoretical; D008968:Molecular Conformation; D010196:Pancreatic Elastase / Q000737:chemistry*; D011487:Protein Conformation; D012984:Software; D012997:Solvents; D013552:Swine
chemical_list: D012997:Solvents; D010196:Pancreatic Elastase