Alternative models for two crystal structures of bovine rhodopsin.

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).