Modelling prior distributions of atoms for macromolecular refinement and completion.
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.
Roversi
P
P
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, England.
Blanc
E
E
Vonrhein
C
C
Evans
G
G
Bricogne
G
G
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
D012997:Solvents; D010196:Pancreatic Elastase