Python-based
Hierarchical
ENvironment
for
Integrated
Xtallography
Contents
morph_model is a procedure for distorting a model to match an electron density map. It is suited for a case where a poor but unbiased map is available and a model that is generally locally similar to the target structure but where longer-range distances are not conserved. This is often the case in homologous structures.
The basic idea in morph_model is to apply a smoothly-varying offset to the template structure so as to make it match the map as closely as possible. In this way information about the local structure of the template is retained while allowing longer-range changes in structure.
Morphing is carried out in 3 steps:
After morphing, the morphed model is refined. This process is then repeated morph_cycles (typically 6) times.
Normally you should specify that morph-model use a prime-and-switch map (map_type=prime_and_switch), as that is usually the most effective map for morphing. You can however choose instead to use a 2mFo-DFc map, a density-modified map, or an omit map. The prime-and-switch map is a map calculated in the same way as a density-modified map, except that once the initial model-based map is calculated (priming), the model information is no longer used (switching). This map is typically quite unbiased by the model.
Running morph_model is easy. If you have a template (coords1.pdb) and a data file fobs.mtz with FP SIGFP and FreeR_flag, you can type:
phenix.morph_model data=coords1.mtz model=coords1.pdb
and morph_model will run automatically.
If you have your own map you want to use in morph_model, you can type:
phenix.morph_model data=coords1.mtz \ model=coords1.pdb map_coeffs=my_map_coeffs.mtz
and morph_model will start off with your map coefficients instead of calculating a new map. If you specify update_map=True (default) then new maps will be calculated on each subsequent cycle. If you specify update_map=False then your map will be used throughout.
You can morph just one part of your model if you want. You can specify it like this:
phenix.morph_model data=coords1.mtz \ model=coords1.pdb morph_selection="chain A"
The remainder of the model will be refined but not morphed.
Usually you will want to edit a parameters file so that you can specify more details of the run. You can get a default parameters file with:
phenix.morph_model
and then just edit the file morph_model_params.dat.
{{phil:phenix.command_line.morph_model}}