[Chimera-users] Calculate RMSD over SSE of NMR ensemble

[Tom Goddard]

Hi Markus,

  There is no special function to compute RMSD of each secondary structure element in an NMR ensemble.  But it is pretty easy to do.  Open the NMR ensemble and display the sequence of the first structure (menu Tools / Sequence / Sequence).  Now the ugly part.  You need all your structures “associated” with the shown sequence, so use the Sequence dialog menu Structure / Associations… and set every structure in the NMR ensemble to be associated with the sequence.  This involves clicking a separate check button (associate with best match) for each of the structures and is a real pain for 25 structures.  Maybe there is a better way of doing it that Chimera sequence experts Elaine and Eric would know.  Once you do that if you drag a box in the sequence window around an alpha helix (each helix is shown as yellow in the sequence) then it reports the RMSD (CA atoms all pairwise distances treated equally) for the selected helix.  These are also reported in the Chimera reply log (menu Favorites / Reply Log).  Even if you were willing to type the residue ranges for each secondary structure element, I don’t know of a Chimera command that will do it since the “rmsd” command only takes 2 structures at a time.  Would be nice if something like "rmsd #0:51-60 at CA ensemble true” would compute the RMSD for those residues for all the members of NMR ensemble #0, but we don’t currently support that.

  One more thing to note — the sequence dialog RMSD calculation is not RMSD of all ensemble members to an average structure.  Instead it looks at all pairwise distances between matched atoms in the N structures (so N*(N-1)/2 pairs) and averages those.  An RMSD to an average structure would be smaller.

  A related question of finding per-residue RMSD values within an NMR ensemble was answered earlier

	http://plato.cgl.ucsf.edu/pipermail/chimera-users/2014-January/009526.html

    Tom


On Jul 10, 2014, at 2:29 PM, Markus Heller <mheller at cdrd.ca> wrote:

> Hello,
>  
> The subject says it all.  How do I calculate the RMSD of secondary structure elements of an NMR ensemble?  I did RTFM, but I’m hoping that I can avoid spelling out the residues comprising the SSEs …
>  
> Thanks and Cheers
> Markus
>  
> --
> Markus Heller, Ph.D.
> NMR Scientist
> CDRD - The Centre for Drug Research and Development
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