[Chimera-users] Selecting residues with zones when reference is absent

[Carlos G. Oliver]

Hello,

I would like to select all ligands that are within a distance of nucleic acids but above a distance from proteins.

The selection command I have so far is:

`select nucleic acid z<10 & protein z>10 & ligand`

This works for PDBs that contain both nucleic acids and protein.

However, some will only contain nucleic acids, and in this case the `protein z>10` condition will result in an empty selection even when there is a valid ligand.

I was wondering if there was a way to check whether the model contains protein to run a different selection command for each case, or to use a different selection command which handles both cases.

Thanks!

Carlos G. Oliver
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