title: Upgrading the twin variables algorithm for large structures.
abstract: Phase extension from lower to higher resolution by using an upgraded TWIN variables algorithm [Hountas & Tsoucaris (1995). Acta Cryst. A51, 754-763] in protein molecules with close to 1,000 non-H atoms is presented. Three points of this procedure are of particular interest. (i) The use of a set of auxiliary variables providing a satisfactory fit for many kinds of constraints: the new algorithm works efficiently despite the extreme 'dilution' of very limited initial phase information into a much larger set of auxiliary variables. (ii) The extension of this auxiliary variables set beyond the resolution of the observed data, which enhances the phase extension in a so-called 'super-resolution' sphere. (iii) The use of the crystallographic symmetry as a new figure of merit and as a reliable test for the correctness of the phase-extension process allows an efficient screening.
authors.affiliation: Physics and Meteorology Laboratory, Agricultural University of Athens, Greece.
authors.forename: K
authors.initials: K
authors.lastname: Bethanis
authors.forename: P
authors.initials: P
authors.lastname: Tzamalis
authors.forename: A
authors.initials: A
authors.lastname: Hountas
authors.forename: A F
authors.initials: AF
authors.lastname: Mishnev
authors.forename: G
authors.initials: G
authors.lastname: Tsoucaris
mesh_terms: D000465:Algorithms; D018360:Crystallography, X-Ray; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D011506:Proteins