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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:
In general, one has to try several different starting elbow angles
10 apart) and repeat steps 3--6 until a good solution is found.
This strategy is also applicable to other multidomain proteins
or 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. 17.1.
- 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 PC-refinement.
- 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
- Rigid-body refinement.
Figure 17.1: Overview of molecular replacement.
Sat Mar 11 09:37:37 PST 1995