title: Iterative projection algorithms in protein crystallography. II. Application.
abstract: Iterative projection algorithms (IPAs) are a promising tool for protein crystallographic phase determination. Although related to traditional density-modification algorithms, IPAs have better convergence properties, and, as a result, can effectively overcome the phase problem given modest levels of structural redundancy. This is illustrated by applying IPAs to determine the electron densities of two protein crystals with fourfold non-crystallographic symmetry, starting with only the experimental diffraction amplitudes, a low-resolution molecular envelope and the position of the non-crystallographic axes. The algorithm returns electron densities that are sufficiently accurate for model building, allowing automated recovery of the known structures. This study indicates that IPAs should find routine application in protein crystallography, being capable of reconstructing electron densities starting with very little initial phase information.
authors.affiliation: Computational Imaging Group, Department of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: Victor L
authors.initials: VL
authors.lastname: Lo
authors.affiliation: School of Biological Sciences, The University of Auckland, Auckland, New Zealand.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Kingston
authors.affiliation: Computational Imaging Group, Department of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: Rick P
authors.initials: RP
authors.lastname: Millane
mesh_terms: D000465:Algorithms; D018360:Crystallography, X-Ray / Q000379:methods*; D008956:Models, Chemical; D011506:Proteins / Q000737:chemistry*
chemical_list: D011506:Proteins
keywords: density modification; iterative projection algorithms; phase determination; phasing