Open AccessWith phases: how two wrongs can sometimes make a right
Author(s) -
Roversi Pietro,
Johnson Steven,
Lea Susan M.
Publication year - 2010
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444909048112
Subject(s) - molecular replacement , substructure , multiple isomorphous replacement , phaser , atom (system on chip) , flattening , chemistry , chemical physics , computer science , crystallography , materials science , crystal structure , physics , diffraction , x ray crystallography , optics , structural engineering , engineering , embedded system , composite material
In isolation, both weak isomorphous/anomalous difference signals from heavy‐atom derivatization and phases from partial molecular‐replacement solutions for a subset of the asymmetric unit often fall short of producing interpretable electron‐density maps. Phases generated from very partial molecular‐replacement models (if generated carefully) can be used to reliably locate heavy‐atom sites, even if the signal is not sufficiently strong to allow robust finding of the sites using Patterson interpretation or direct methods. Additional advantages are that using molecular‐replacement phases to define the heavy‐atom substructure avoids the need for subsequent hand determination and/or origin‐choice reconciliation and that the partial model can be used to aid the mask determination during solvent flattening. Two case studies are presented in which it was only by combining experimental and molecular‐replacement phasing approaches that the crystal structures could be determined.