<br><br><div class="gmail_quote">On Fri, Feb 17, 2012 at 2:12 PM, Justin A. Lemkul <span dir="ltr"><<a href="mailto:jalemkul@vt.edu">jalemkul@vt.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im"><br>
<br>
Steven Neumann wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello Justin,<br>
<br>
As you recommended I run longer pulling of my ligand. I pull the ligand which is on the top of my protein so the top of the protein is pulled so that the whole protein rotated app. 30 degrees - the low part of the protein came out of the box due to the rotation. After app 600 ps the ligand does not move any more and the force applied increase linearly. As I saw the trajectory, ligand does not collide with a periodic image but it does not move. Please, see attacheg plot force vs time. Can you explain why the force increase linearly and ligand is not pulled any more? This is my mdp file for pulling:<br>
<br>
</blockquote>
<br></div>
Is the pulled distance greater than half of the box vector in z? That's the only reason I can see things going haywire. With simple "distance" geometry, there are some limitations like that. Rotation itself is not a problem. You're separating two objects; there's no clear orientation dependence in that case.<br>
<br>
-Justin<br></blockquote><div><br><br>As you can see the pulling distance is 5 nm. The lenght of my box in Z direction is 12 nm. Thus, it is not. Any other ideas? <br></div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
title = Umbrella pulling simulation<br>
; Run parameters<br>
integrator = md<br>
dt = 0.002<br>
tinit = 0<br>
nsteps = 500000 ; 500 ps<br>
nstcomm = 10<br>
; Output parameters<br>
nstxout = 5000 ; every 10 ps<br>
nstvout = 5000<br>
nstfout = 500<br>
nstxtcout = 500 ; every 1 ps<br>
nstenergy = 500<br>
; Bond parameters<br>
constraint_algorithm = lincs<br>
constraints = all-bonds<br>
continuation = yes ; continuing from NPT<br>
; Single-range cutoff scheme<br>
nstlist = 5<br>
ns_type = grid<br>
rlist = 0.9<br>
rcoulomb = 0.9<br>
rvdw = 0.9<br>
; PME electrostatics parameters<br>
coulombtype = PME<br>
fourierspacing = 0.12<br>
fourier_nx = 0<br>
fourier_ny = 0<br>
fourier_nz = 0<br>
pme_order = 4<br>
ewald_rtol = 1e-5<br>
optimize_fft = yes<br>
; Temperature coupling is on<br>
tcoupl = V-rescale ; modified Berendsen thermostat<br>
tc_grps = Protein_LIG Water_and_ions ; two coupling groups - more accurate<br>
tau_t = 0.1 0.1 ; time constant, in ps<br>
ref_t = 298 298 ; reference temperature, one for each group, in K<br>
; Pressure coupling is on<br>
Pcoupl = Parrinello-Rahman<br>
pcoupltype = isotropic<br>
tau_p = 1.0 compressibility = 4.5e-5<br>
ref_p = 1.0<br>
; Generate velocities is off<br>
gen_vel = no<br>
; Periodic boundary conditions are on in all directions<br>
pbc = xyz<br>
; Long-range dispersion correction<br>
DispCorr = EnerPres<br>
; Pull code<br>
pull = umbrella<br>
pull_geometry = distance ; simple distance increase<br>
pull_dim = N N Y<br>
pull_start = yes ; define initial COM distance > 0<br>
pull_ngroups = 1<br>
pull_group0 = Protein<br>
pull_group1 = LIG182<br>
pull_rate1 = 0.01 ; 0.01 nm per ps = 10 nm per ns<br>
pull_k1 = 200 ; kJ mol^-1 nm^-2<br>
<br>
Would you recommend position restrained of the protein backbone atoms or e.g. residues from the lower part so that the protien will not roatate?<br>
<br>
Thank you,<br>
<br>
Steven<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
On Fri, Feb 17, 2012 at 10:41 AM, Steven Neumann<br></div></div><div class="im">
<<a href="mailto:s.neumann08@gmail.com" target="_blank">s.neumann08@gmail.com</a> <mailto:<a href="mailto:s.neumann08@gmail.com" target="_blank">s.neumann08@gmail.com</a>><u></u>> wrote:<br>
<br>
<br>
<br>
<br>
<br>
On Mon, Feb 13, 2012 at 2:53 PM, Steven Neumann<br></div><div class="im">
<<a href="mailto:s.neumann08@gmail.com" target="_blank">s.neumann08@gmail.com</a> <mailto:<a href="mailto:s.neumann08@gmail.com" target="_blank">s.neumann08@gmail.com</a>><u></u>> wrote:<br>
<br>
Thank you Justin!<br>
<br>
<br>
On Mon, Feb 13, 2012 at 2:44 PM, Justin A. Lemkul<br></div><div class="im">
<<a href="mailto:jalemkul@vt.edu" target="_blank">jalemkul@vt.edu</a> <mailto:<a href="mailto:jalemkul@vt.edu" target="_blank">jalemkul@vt.edu</a>>> wrote:<br>
<br>
<br>
<br>
Steven Neumann wrote:<br>
<br>
Thank you Justin. I run my pulling using two force<br>
constant for pulling. K1=100 and K1=200<br>
Please, see attached plots of force vs time. Is<br>
there any criteria to adjust pulling constant? Would<br>
you suggest running it for a longer time?<br>
<br>
<br>
I know of no systematic study for choosing a force<br>
constant. Guessing wildly at what's going on, I'd say<br>
you need longer simulations as it appears you have only<br>
just caused dissociation towards the end of the 500 ps.<br>
<br>
-Justin<br>
<br>
Steven<br>
<br>
On Mon, Feb 13, 2012 at 1:11 PM, Justin A. Lemkul<br>
<<a href="mailto:jalemkul@vt.edu" target="_blank">jalemkul@vt.edu</a> <mailto:<a href="mailto:jalemkul@vt.edu" target="_blank">jalemkul@vt.edu</a>><br></div>
<mailto:<a href="mailto:jalemkul@vt.edu" target="_blank">jalemkul@vt.edu</a> <mailto:<a href="mailto:jalemkul@vt.edu" target="_blank">jalemkul@vt.edu</a>>>><div><div class="h5"><br>
wrote:<br>
<br>
<br>
<br>
Steven Neumann wrote:<br>
<br>
Dear Gmx Users,<br>
Is it always required to restrained<br>
positions of the protein<br>
while pulling your ligand? My system is made<br>
of 10 ligands<br>
attached to my protein surface. I am pulling<br>
one of them.<br>
<br>
<br>
No, it is not required. I assume you've gotten<br>
this idea from my<br>
tutorial - the restraints there were used for a<br>
very specific<br>
purpose (detailed in the paper linked from the<br>
tutorial).<br>
<br>
<br>
I have just seen trajectory of pulling my<br>
ligand without<br>
restraining positions of protein and 9<br>
remaining ligands. My<br>
ligand while pulling also pulled the protein<br>
with itself (for 1<br>
nm distance) and then splited. Is is this<br>
approach more reliable?<br>
<br>
If your goal is umbrella sampling, you need only<br>
generate a series<br>
of reasonable starting configurations along a<br>
defined reaction<br>
coordinate. The absolute positions are<br>
irrelevant; it is the<br>
relative distance that matters.<br>
<br>
-Justin<br>
<br></div></div>
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Virginia Tech<br>
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-- <br>
==============================<u></u>==========<br>
<br>
Justin A. Lemkul<br>
Ph.D. Candidate<br>
ICTAS Doctoral Scholar<br>
MILES-IGERT Trainee<br>
Department of Biochemistry<br>
Virginia Tech<br>
Blacksburg, VA<br>
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