Pawan Kumar wrote:
Respected Sir,
Greetings from Pawan.
I have edited the lipid.itp file to add just one line extra " H atom
from the opls_force_filed.itp " at the end of lipid interactions data
and that works fine.
I have done this after seeing the archives. It was given either I should
change the file for sigma and epsilon values or else just add this line.
I think I have done it correctly. If not please correct me.
No, that is incorrect. You need to add the additional atom type as well as
convert C6/C12 to sigma/epsilon. Otherwise, the calculated nonbonded
interactions are meaningless. Read instructions carefully!
Force fields have to be internally self-consistent, so using the parameters from
OPLS with Berger lipids will give spurious results. The only proper
combinations are Gromos/Berger or OPLS/converted Berger.
I have removed the position restraints after the inflategro procedure.
After that I did energy minimization using define = -DFLEXIBLE.
I will change the temperature as per your suggestion.
I thought before solvating if I do position restraint mdrun the lipids
will compact more surrounding the protein.
No, your system will probably explode due to unsatisfied charge interactions and
hydrogen bonds. There is a substantial dipole in each lipid headgroup that can
repel the lipids away from each other if it is not shielded.
Thats the step when I got Lincs warnings and segmentation fault.
Then I tried solvating the system using genbox step and spc216.gro as
the solvent.
But before doing the solvation step I copied the vdwradii.dat file into
the working directory and increased the value for carbon to 0.5.
But the result of this was " Segmentation fault " again. Can you please
tell me why I get the " Segmentation fault " here in this step.
The command used was : genbox -cp comp_em27.pdb -cs spc216.gro -o
box.pdb -p topol.top
Using a 0.5-nm radius for carbon will cause problems of excess memory
consumption, or otherwise breaks the calculation. Use something more along the
lines of 0.35 or 0.375, and manually delete out any stray waters in the
hydrophobic core.
-Justin
Thanking you,
Yours sincerely,
Pawan
On Tue, Mar 31, 2009 at 4:20 PM, Justin A. Lemkul <jalem...@vt.edu
<mailto:jalem...@vt.edu>> wrote:
Justin A. Lemkul wrote:
Pawan Kumar wrote:
Respected Sir,
Greetings from Pawan.
I have used force constants of 100000 in position restraint
.itp files for proteins as suggested in Dr. Tieleman' s
webisite for Inflategro.
The mdp files are :
The .mdp files look reasonable enough, although I don't know why
you are applying position restraints during EM. If it is for
InflateGRO, that is fine, but once the system is assembled, you
should remove the position restraints from the protein to
minimize the system more.
And are you sure you want 300K? DPPC will be in a gel phase at
that temperature. If you want a more realistic fluid-phase
model, you'll have to go above 315K (323K is common).
One thing I just noticed. You don't have solvent in your
position-restrained run? That could be a big problem if the lipid
headgroups are strongly repelled from one another. Add solvent
before doing anything other than EM.
-Justin
*Topology file :*
; Include forcefield parameters
#include "ffoplsaa.itp"
#include "lipid.itp"
#include "dppc.itp"
This section should not work, as written. Have you modified
lipid.itp according to Chris Neale's half-epsilon
double-pairlist method? If not, what you've done makes no
sense. The Berger lipid parameters distributed through
Tieleman's site are designed for use with the Gromos force
fields. They can be modified (search in the archives), but that
can also be a source of error. Users who have made mistakes in
the conversion have seen their systems explode.
-Justin
; Include chain topologies
#include "topol_A.itp"
#include "topol_B.itp"
#include "topol_C.itp"
;#ifdef POSRES
;#include "lipid_posre.itp"
;#endif
; Include water topology
#ifdef FLEX_SPC
#include "flexspc.itp"
#else
#include "spc.itp"
#endif
#ifdef POSRES_WATER
; Position restraint for each water oxygen
[ position_restraints ]
; i funct fcx fcy fcz
1 1 1000 1000 1000
#endif
; Include generic topology for ions
#include "ions.itp"
[ system ]
; Name
PROTEIN IN DPPC BILAYER
[ molecules ]
; Compound #mols
Protein_A 1
Protein_B 1
Protein_C 1
DPPC 926
;SOL 23552
Please help with some suggestions.
Thanking you,
Yours sincerely,
Pawan
On Mon, Mar 30, 2009 at 6:22 PM, Justin A. Lemkul
<jalem...@vt.edu <mailto:jalem...@vt.edu>
<mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>> wrote:
Pawan Kumar wrote:
Respected Sir,
Greetings from Pawan.
I did the Inflategro procedure for the POPC bilayer
generated
using genconf.
It took around 26 compressions for coming near the
initial area
(just above it).
The minimization were all converged to Fmax < 1350.
If I decrease the Fmax less than this I am getting
machine
precision.
But when I proceeded with the final compressed
structure for pr
mdrun it gave lincs warnings and ended with
segmentation fault.
As an alternative to this bilayer I used the DPPC bilayer
(pre-equilibrated) which is given in GMX-Benchmark
distribution.
I carried out the same steps of Inflategro. I used
the cutoff of
14 A in the inflation and compression step also.
In this case the the Steepest Descents converged to
Fmax < 1000
in all the steps. The maximum force war never above 850.
But when I did position restraint mdrun with the last
compressed
file I got Lincs warnings and Segementation fault
after few
steps (30 - 40 steps).
Can you please help how to proceed ?
If the minimization procedure is adequately finishing,
then the
problem comes from something you are doing. If you post
your .mdp
file, we may be able to see if there are any obvious
mistakes.
-Justin
Thanking you,
Yours sincerely,
Pawan
Justin A. Lemkul
Graduate Research Assistant
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu <http://vt.edu> <http://vt.edu> |
(540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
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--
========================================
Justin A. Lemkul
Graduate Research Assistant
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu <http://vt.edu> | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
========================================
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--
========================================
Justin A. Lemkul
Graduate Research Assistant
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
========================================
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