[gmx-users] Umbrella sampling along a dihedral angle

Justin Lemkul jalemkul at vt.edu
Sat Dec 27 15:49:35 CET 2014

On 12/26/14 6:11 PM, Nash, Anthony wrote:
> Dear Gromacs community,
> Using enforced rotation potentials I have generated a really smooth rotation
> of my ligand the catalytic binding domain of my protein. I then put together
> a simple perl script to calculate the dihedral angle of four particular atoms
> at each time step using g_angle. Taking a 6 degree interval (for a total of
> 60 windows to span the 360 degree rotation) I modified the topology with a [
> dihedral_restraint ] with the respective dihedral angle for that particular
> configuation. I plan on then running each window for 10 ns to begin with
> (according to the PMF profile I can add more time). It is from this point
> where I am a little stuck.
> I have gone through a number of posts going back to 2011 with regards to
> using umbrella sampling along a dihedral angle reaction coordinate. The
> precise post was from Justin:
> "You'll have to build various configurations that correspond to different
> dihedral angles (which form the sampling windows), then restrain them.
> The energy attributed to the restraints is then stored in the .edr file. From
> these energies, you should be able to construct the energy curve over the
> sampling windows. There are examples of this in the literature, so I suspect
> you should be able to find some demonstrations of how it's applied."
> I was wondering whether gromacs now support this procedure natively? I
> noticed g_wham has an option -cycl for dihedrals but I am still not sure how
> this fits in with the traditional gromacs means of generating pull force
> output as I have only been using distance based rather than angular based
> umbrella sampling.

g_wham is still only really designed to process the output from the pull code, 
not any generalized restraint.  That would be a nice features, but AFAIK it is 
not in the pipeline.  You can de-bias the results like I suggested above, but 
it's probably more work than it's worth.  I would suggest just using Alan 
Grossfield's WHAM implementation.  There, you just need to provide the raw 
numbers (in this case, the dihedral values) and the force constants used.  It 
will then give you your PMF.  We have done this recently; it is very easy.



Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441


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