Yeah, Crystal wrote all the initial code for GIST and knows the
implementation better than anybody.
rereading the emails from the other person with this problem (which Crystal
also solved), there was both a problem with imaging (not using familiar
with an octahedral box) but also with the RMS fit. The RMS fit does seem
consistent with the problems you are having. If you cut out the voxels
within a a few angstroms (3.5+ about), where the minimum image makes no
difference then you should be okay with the analysis you have.
That being said, with GIST, as Dan and Crystal mention, it's probably best
just to restrain enough heavy atoms in the system to prevent the
translation and rotation of the solute altogether. For proteins, a
technique which we often use is to restrain a few sites (at least 3 non
linear heavy atoms) distal from the region of the interest (often a protein
active site) and preferably restrain heavy atoms with low b-factors. The
aim of this is to maintain as much important motion in the system while
simultaneously preventing the translation and solute. We also tend to run
systems with all heavy atoms restrained and with main chain heavy atoms
restrained. We generally run all three (each is informative in its own
way).
Tom
On Mon, Aug 10, 2015 at 8:12 PM, Daniel Roe <daniel.r.roe.gmail.com> wrote:
> Hi,
>
> On Mon, Aug 10, 2015 at 3:49 AM, Thomas Fox <thomas_fox.gmx.net> wrote:
> > Eww values equal 0, but then 8 voxels with energies up to 300
> kcal/mol. The
> > neigboring voxels of these high-energy ones have what I would consider
> > "normal" values.
> >
> > This behavior becomes extremely pronounced when I use a larger grid
> for my
> > gist calculation (for a 41x41x41 grid with a spacing of 0.5A, I get
> energy
> > values up to 1E19, and about 13000 of the 68921 data points have a
> Eww-norm
> > > 100 kcal/mol.
> >
> >
> > parm cb7_solv.top
> > trajin cb7_solv.crd
> > trajin prod.traj.nc 1 5000
> > autoimage origin
> > rmsd CUC :1 first
>
> I would bet the large values you are seeing are the result of
> collisions caused by RMS-fitting after imaging (as mentioned by
> Crystal). The problem is that GIST uses imaged distances in it's
> calculations, but once you RMS-fit a system it is almost always
> rotated away from the original unit cell axes and so imaging no longer
> works properly (which is why cpptraj prints out a warning to this
> effect when RMS-fitting a system with PBC). For small rotations the
> effect may not be noticeable, but it's there. The effect is more
> pronounced for atoms farther away from the rotation which is why
> increasing the grid size gives you more clashes.
>
> As implied by Crystal probably the best way to ensure you get a well
> behaved grid at the moment is to put some mild positional restraints
> on your solute. On my current to-do list is to have a grid which can
> "move" with the solute using the RMS results - I hope to have this
> implemented soon.
>
> Hope this helps,
>
> -Dan
>
> >
> > gist gridcntr 0. 0. 0. griddim 21 21 21 gridspacn 0.5 out
> gist_21_05.out
> >
> > run
> > _______________________________________________
> > AMBER mailing list
> > AMBER.ambermd.org
> > http://lists.ambermd.org/mailman/listinfo/amber
>
>
>
> --
> -------------------------
> Daniel R. Roe, PhD
> Department of Medicinal Chemistry
> University of Utah
> 30 South 2000 East, Room 307
> Salt Lake City, UT 84112-5820
> http://home.chpc.utah.edu/~cheatham/
> (801) 587-9652
> (801) 585-6208 (Fax)
>
> _______________________________________________
> AMBER mailing list
> AMBER.ambermd.org
> http://lists.ambermd.org/mailman/listinfo/amber
>
--
************************************************
Tom Kurtzman, Ph.D.
Assistant Professor
Department of Chemistry
Lehman College, CUNY
250 Bedford Park Blvd. West
Bronx, New York 10468
718-960-8832
http://www.lehman.edu/faculty/tkurtzman/
<http://www.lehman.edu/faculty/tkurtzman/index.html>
************************************************
_______________________________________________
AMBER mailing list
AMBER.ambermd.org
http://lists.ambermd.org/mailman/listinfo/amber
Received on Mon Aug 10 2015 - 11:00:04 PDT
