In principle, I would love to do this... in practice life has gotten in the way lately. Some of the groundwork has been set - the OpenMM developer, Peter Eastman, implemented support for arbitrary symmetry constraints a while back, but (to my great chagrin, considering I was the one most strongly asking for it) I'm not currently in a position to find the (rather significant) amount of development time needed to actually apply it in ISOLDE. When considering all the ramifications, it becomes clear that a lot of code would need to be changed. So I'm afraid this is one feature that isn't on the visible horizon for now.

Best,
Tristan

On Fri, Feb 28, 2025 at 10:26 AM Guillaume Gaullier <guillaume.gaullier@kemi.uu.se> wrote:

Hello,


I agree this would be convenient!


In the meantime, I find that using the symmetry-expanded model from servalcat in ISOLDE is a mostly decent workaround (and probably what you do as well).

I simply ignore the additional chains (they are there just to please the MD force field, so all interactions make sense and there isn't too much empty map), I work only on the set of chains making up the asymmetric unit, and feed this to the next round of refinement with servalcat.


But this approach is quickly limiting when placing waters and ligands at the interface between asymmetric units, because they don't necessarily get assigned to the correct chains (the ones that I consider my working copy). This particular problem would be best handled by accounting for point group symmetry as you suggest.

And I suppose it would also be computationally lighter to handle symmetry than to use the fully expanded model, especially during the initial settling stage when running a simulation on the entire model.


Cheers,


Guillaume


From: Oliver Clarke via ChimeraX-users <chimerax-users@cgl.ucsf.edu>
Sent: Thursday, February 27, 2025 5:41:47 PM
To: Tristan Croll
Cc: ChimeraX Users Help
Subject: [chimerax-users] NCS in ISOLDE?
 
Hi Tristan,

I was wondering if there is any update on NCS in ISOLDE?

Specifically, given that ISOLDE has live crystallographic symmetry (where the sym copies are represented as ghosts), would there be any possibility of implementing the same approach for point group symmetry - where the user provides the asymmetric unit and point group symmetry, and ISOLDE refines with point group sym ghosts?

This would be convenient, especially for interoperability with SERVALCAT, which implements this approach to point group & helical symmetry (very handy for many cryoEM structures that are refined with symmetry applied!).

Cheers
Oli


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