[Chimera-users] Create a protein model using Chimera?

[Elaine Meng]

Hello Maja,
It depends if there are atoms of overlap between the two parts.

If there are overlapping parts, for example one structure is residues 1-15 and the other is residues 12-500: you can position the structures relative to each other by superimposing just the overlapping atoms using the "match" command (for example, something like "match #0:12-15 at n,ca,c,o #1:12-15 at n,ca,c,o"). Note the numbering won't necessarily be the same in the two structures, so you need to check on exactly which residues should be superimposed.  Then you  would delete the overlapping atoms from one structure (since the "same" atoms are already in the other structure), combine the two structures into one model, and then add a bond between the two parts.  This could all be done in Chimera (see commands "delete" "combine" "bond", or graphical interfaces for the latter two are Favorites...Model Panel "copy/combine" function and Tools...Structure Editing... Build Structure, Adjust Bonds tab), OR it could be done by manually text-editing PDB files, after the matching step described above and then saving one structure as PDB "relative to" the other structure.  Documentation for commands, command-line atom specification, and Build Structure:
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/framecommand.html>
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/frameatom_spec.html>
<http://www.rbvi.ucsf.edu/chimera/docs/ContributedSoftware/editing/editing.html>

If there are not overlapping parts, for example one structure is residues 1-15 and the other is residues 16-500, you would just use the Join Models tab in the Build Structure tool mentioned above:
<http://www.rbvi.ucsf.edu/chimera/docs/ContributedSoftware/editing/editing.html#join>

YOu can see there are fewer steps in the latter, but it can be hard to fully specify the correct geometry at the join.  Thus when overlapping atoms in similar conformations are available, that more complicated overlapping procedure may produce better results than simply deleting the redundant atoms and using the second approach.

Best,
Elaine
-----
Elaine C. Meng, Ph.D.                       
UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab
Department of Pharmaceutical Chemistry
University of California, San Francisco



On Oct 18, 2013, at 2:26 AM, Maja Divjak wrote:

> Hello again Elaine,
> 
> And further to that, how do I put the two molecules together please, now that I have a possible propeptide for IL-1beta? I had a go using MatchMaker with best-aligning pair of chains and everything else at default, but I'm not sure if this is the best approach? The propeptide bound via it's N-terminus to the C-terminus of IL-1 (in rainbow depiction) and the propeptide is supposed to be at the N-terminus of the whole. Apologies it this seems totally lame, but protein structure is not my forte...
> 
> I look forward to your reply,
> 
> Thank you and best wishes,
> 
> Maja
> 
> On Oct 18, 2013, at 7:28 PM, Maja Divjak wrote:
> 
>> Hi Elaine,
>> 
>> Thanks for the reply. I ended up using Modeler, which after much frustration, gave me some reasonable models.
>> 
>> Thank you and best wishes,
>> 
>> Maja