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# Generalized Molecular Replacement

The following sections show how the 26-10 Fab fragment complexed with digoxin was solved by generalized molecular replacement (Brünger, 1991c). The space group of the 26-10 Fab/digoxin crystals is (Strong, 1990), with the b-axis unique, and a non-crystallographic twofold symmetry is present. The following strategy was employed to solve the structure:- Self-rotation function.
- Modification of the elbow angle of a known Fab structure.
- Cross-rotation function with the modified Fab structure.
- Filtering the rotation function by -refinement.
- Analysis of the -refinement.
- Translation function for molecule A, using the -refined model.
- Translation function for molecule B.
- Combined translation function to determine the relative position between A,B.
- Rigid-body refinement.

*PC-*refinements of other degrees of freedom. The modification of the Fab example input files should be straightforward. An overview of the strategy is shown in Fig. 19.1.

**Subsections**

- Self-rotation Function
- Modification of the Elbow Angle of a Known Fab Structure
- Cross-Rotation Function with the Modified Fab Structure
- PC-Refinement of the Highest Peaks of the Cross-Rotation Function
- Analysis of the PC-refinement
- Translation Function for Molecule A Using the PC-refined Model
- Translation Function for Molecule B
- Combined Translation Function to Determine the Relative Position between A and B
- Rigid-Body Refinement

*Xplor-NIH 2024-09-13*