[gmx-users] Re: Re: Bonds break while Minimising using distance restraints
Justin A. Lemkul
jalemkul at vt.edu
Wed Sep 3 22:56:58 CEST 2008
plmallip at mail.uh.edu wrote:
> Hi,
>
> There is no chance of steric clashes between 6151 & 6160. They are
> seperated by 12 A. ("Warning: 1-4 interaction between 6151 and 6160 at
> distance 1.387 which is larger than the 1-4 table size 1.000 nm. These
> are ignored for the rest of the simulation. This usually means your
> system is exploding") I cannot build the missing residues without
> knowing the secondary structure. I am already running one simulation
> with built residues. But, my ultimate goal is to run dynamics with
> distance restraints.
Are you sure you are identifying the correct atoms? A 1-4 interaction involves
atoms that are very close together (in fact, three bonds away). Are you saying
that they are separated by 12 A (1.2 nm) or by 12 nm? If they are starting 12 A
(1.2 nm) away, then the error message still makes sense. If they are 12 nm
away, then I suspect that some sort of bond or restraint is being applied
improperly.
I thought you were applying a 12-nm distance restrain to atoms in the 7000's, so
I'm confused as to why atoms 6151 and 6160 should be 12 nm apart (assuming, of
course, that you meant to say nm instead of A :)
-Justin
>
> My sytem is an pentamer. Here is the toplogy file
>
> ; Include forcefield parameters
> #include "ffG43a1.itp"
>
> ; Include chain topologies
> #include "chnrc_A.itp"
> #include "chnrc_B.itp"
> #include "chnrc_C.itp"
> #include "chnrc_D.itp"
> #include "chnrc_E.itp"
>
> ; Include water topology
> #include "spce.itp"
>
> #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 water
>
> [ molecules ]
> ; Compound #mols
> Protein_A 1
> Protein_B 1
> Protein_C 1
> Protein_D 1
> Protein_E 1
> SOL 55419
> NA+ 54
>
>
> Thanks & regards,
> Latha.
>
> > > plmallip at mail.uh.edu wrote:
> > >
> > > Hi Justin, thanks for your response. You are right. I get the
> > following
> > > message in the .job file
> > >
> > > "Warning: 1-4 interaction between 6151 and 6160 at distance
> > 1.387 which
> > > is larger than the 1-4 table size 1.000 nm
> > > These are ignored for the rest of the simulation
> > > This usually means your system is exploding"
> > >
> > > The atoms I restrained are 1703 & 1712 (6151 & 6160 atoms are
> > also from
> > > the same residues). The distance between them is 12 A (there
> > are 14
> > > missing residues in between). My aim is to use distance
> > restraints,
> > > without building missing residues in between. Is there any way
> > I can
> > > overcome this warning why minimizing the system?
> >
> > It's very hard to say, because none of us knows what's in your
> > system, topology,
> > or how you built things :)
> >
> > You have some type of nasty steric clash that's driving atoms
> > 6151 and 6160
> > apart. Visualize the trajectory (.trr) to see if you can
> > identify where things
> > start to break down. I don't know if the distance
> > restraint has anything to do
> > with the problem or not.
> >
> > Is there a problem with building missing residues? That
> > might make life quite a
> > bit easier in the long run.
> >
> > -Justin
> >
> > >
> > > Thanks & regards,
> > > Latha.
> > >
> > >
> > > > Dear colleagues,
> > > >
> > > > I need to use simple distance restraints of 12.5 A
> > between two CA atoms
> > > > of two residues. I am using the following lines in the
> > .itp file
> > > >
> > > > #ifdef DDISRES
> > > > [distance_restraints]
> > > > ;ai aj type index type' low
> > up1 up2 fac
> > > > 1703 1712 1
> > 0 1 11.5 12.0
> > 12.5 1.0
> > > >
> > > > The first feww line of .mdp file for minimisation of
> > protein alone is
> > > >
> > > > ; Preprocessing
> > > > ;
> > > >
> > title = ${MOL}
> > > >
> > cpp = /lib/cpp ;Preprocessor
> > > >
> > define = -DDISRES ;For cg, and also steep
> > > >
> > >
> > > You are not actually applying your distance restraint.
> > If you have "#ifdef
> > > DDISRES," then you would have to "define = -DDDISRES" in the
> > .mdp file.
> > > What
> > > you probably meant to define was "#ifdef DISRES" in the topology.
> > >
> > > >
> > After minimisation, the restarined residues & the adjacent
> > > > bonds break. This results in fragmnets - residues
> > alone, peptide bond
> > > > alone and the rest of the protein. The distance
> > restrained residues
> > > > seems to try to move towards each other (6.04 A after
> > minimisation) and
> > > > this might have caused fragmentation. I tried to use
> > various upper and
> > > > lower values for bond length so as to increase
> > flexibility. But, still I
> > > > end up in the fragments.
> > > >
> > >
> > > Bonds don't break in classical MD, this is just an artifact of
> > > visualization,
> > > probably from nasty steric clashes within your structure.
> > >
> > >
> > > > Some
> > of the suggestions in the archive says VMD doesn't show
> > > > bonds if they r above threshold value. When I checked
> > the distances
> > > > between the atoms, one of them is really long CO-CA
> > bond 3.23 A
> > > > (normally its 1.59A). This means the bond is no longer
> > there.> >
> > >
> > > No, the bond is there, VMD just isn't smart enough to see it
> > :) You are
> > > probably well on your way to an explosion if you try to
> > constrain bond
> > > lengths
> > > with LINCS, however.
> > >
> > > -Justin
> > >
> > >
> > > ---------------------------------------------------------------
> > ---------
> > >
> > > _______________________________________________
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> >
> > --
> > ========================================
> >
> > Justin A. Lemkul
> > Graduate Research Assistant
> > 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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--
========================================
Justin A. Lemkul
Graduate Research Assistant
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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