Abstract
The space-group symmetry of two crystal forms of rhodopsin (PDB codes 1gzm and 2j4y; space group P3(1)) can be re-interpreted as hexagonal (space group P6(4)). Two molecules of the G protein-coupled receptor are present in the asymmetric unit in the trigonal models. However, the noncrystallographic twofold axes parallel to the c axis can be treated as crystallographic symmetry operations in the hexagonal space group. This halves the asymmetric unit and makes all of the protein molecules equivalent in these structures. Corrections for merohedral twinning were also applied in the refinement in the higher symmetry space group for one of the structures (2j4y).
Highlights
The space-group symmetry of two crystal forms of rhodopsin (PDB codes 1gzm and 2j4y; space group P31) can be re-interpreted as hexagonal
Two molecules of the G protein-coupled receptor are present in the asymmetric unit in the trigonal models
The noncrystallographic twofold axes parallel to the c axis can be treated as crystallographic symmetry operations in the hexagonal space group
Summary
Departments of Biological Structure and Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, WA 98195, USA. The noncrystallographic twofold axes parallel to the c axis can be treated as crystallographic symmetry operations in the hexagonal space group This halves the asymmetric unit and makes all of the protein molecules equivalent in these structures. The structures of ground-state bovine rhodopsin and of one of its recombinant mutants (N2C/D282C) have been solved in space group P31 (Edwards et al, 2004; Li et al, 2004; Standfuss et al, 2007) with two molecules in the asymmetric unit. In the original crystallographic analysis of the ground-state molecule, the choice of space-group symmetry, i.e. trigonal versus hexagonal, was made mostly on the basis of a reduced = 60 peak in the native rotation function. A twinning fraction of 0.02 was obtained for the ground-state data set (1gzm). [Twinning was reported for the heavy-atom derivative used to solve this structure (Li et al, 2004).]
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