title: Space-group and origin ambiguity in macromolecular structures with pseudo-symmetry and its treatment with the program Zanuda.
abstract: The presence of pseudo-symmetry in a macromolecular crystal and its interplay with twinning may lead to an incorrect space-group (SG) assignment. Moreover, if the pseudo-symmetry is very close to an exact crystallographic symmetry, the structure can be solved and partially refined in the wrong SG. Typically, in such incorrectly determined structures all or some of the pseudo-symmetry operations are, in effect, taken for crystallographic symmetry operations and vice versa. A mistake only becomes apparent when the R(free) ceases to decrease below 0.39 and further model rebuilding and refinement cannot improve the refinement statistics. If pseudo-symmetry includes pseudo-translation, the uncertainty in SG assignment may be associated with an incorrect choice of origin, as demonstrated by the series of examples provided here. The program Zanuda presented in this article was developed for the automation of SG validation. Zanuda runs a series of refinements in SGs compatible with the observed unit-cell parameters and chooses the model with the highest symmetry SG from a subset of models that have the best refinement statistics.
authors.affiliation: CCP4, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0FA, England.
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Lebedev
authors.affiliation: Henry Wellcome Building for Biocatalysis, Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, England.
authors.forename: Michail N
authors.initials: MN
authors.lastname: Isupov
mesh_terms: D001331:Automation; D006801:Humans; D037181:Lectins, C-Type / Q000737:chemistry; D046911:Macromolecular Substances / Q000737:chemistry*; D015394:Molecular Structure; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000737:chemistry
chemical_list: C509771:CLEC5A protein, human; D037181:Lectins, C-Type; D046911:Macromolecular Substances; D011956:Receptors, Cell Surface
keywords: molecular replacement; pseudo-origin; pseudo-symmetry; space group