[Chimera-users] All PDB ca atom pairwise distance

[Eric Pettersen]

Well, since the code is simple, I’ve included it below.  You should put it in a file whose name in “.py” to indicate it’s Python code, then you can run it in Chimera simply by opening it.  It will create a file named “output” in your home folder.  It assumes you’re doing CA-CA distances, not CA-any.  Probably still very slow.

from chimera import openModels, Molecule
mol = openModels.list(modelTypes=[Molecule])[0]
cas = [ a for a in mol.atoms if a.name == “CA” and a.element.name == “C”]
import os.path
f = open(os.path.expanduser(“~/output”), “w”)
for i, ca1 in enumerate(cas):
	for ca2 in cas[i+1:]:
		print>>f, ca1, ca2, ca1.coord().distance(ca2.coord())
f.close()

Since my mail client does wonky things to quotation marks, I’ve also attached the above as a file.

—Eric



> On Oct 31, 2017, at 11:36 AM, Eric Pettersen <pett at cgl.ucsf.edu> wrote:
> 
>> On Oct 31, 2017, at 9:54 AM, Kyle Morris <kylelmorris at berkeley.edu> wrote:
>> 
>> Dear chimera dev and users,
>> 
>> Is there a way to calculate (using the GUI, commands or using a python script) the pairwise distances for every single c-alpha atom in a set of loaded PDB coordinates and spit this out to a file for further analysis? There are 142,800 atoms in the current loaded assembly.
> 
> Do you mean CA-CA distances, or CA-any-other-atom distances?  Even CA-CA only (assuming CAs are roughly 1/10 of your atoms) will be more than one hundred million distances, and CA-other will be more than a billion.  Is this really what you want?  If so, it would seem more efficient and much faster to write a special purpose program for this in a compiled language, like C, C++ or some such.  It is of course doable in Chimera via Python.  If you really do want to do it that way, I can offer further guidance...
> 
> —Eric
> 
> 	Eric Pettersen
> 	UCSF Computer Graphics Lab
> 
> 
> 
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