I'm working on a small project, and need some feedback.

I am trying to rebuild methionine side-chains by looking at the difference peaks for a given Fo-Fc map.

I envision a process as follows:

1. Delete the MET side-chain of a PDB file

2. Refine structure to get Fo-Fc map

3. Get a list of the peak positions relative to the coordinates of the PDB file I used

4. Filter list by keeping peaks near the MET C alpha/beta PDB coordinate.

5. Try to rebuild side-chain after anchoring the sulfur atom (assuming sulfur is located at the highest peak and within some distance to C beta)

What functions should I use to achieve step 3?

I am also trying to implement this process within the ringer program (phenix/cctbx_project/mmtbx/command_line/ringer.py). If anyone is familiar with this, what commands would work best within this ringer program? i.e. what functions can operate on difference_map (which is sampled by a point using tricubic_interpolation under 'def sample_angle')?

I hope this makes some sense to someone.

Thanks!

Alex