I maintain the system tepmerature at 300K. As Karl suggested, to see there
is any effect of temperature on ligand conformation, I would like to try
out few simulations possibly in the range of 283K - 293K.
On Wed, Jan 30, 2013 at 11:31 AM, Bill Ross <ross.cgl.ucsf.edu> wrote:
> > what
> > could be the lowest possible temperature where I can do a classical MD
> > simulation?
>
> What would be your ideal?
>
>
> Bill
>
> aneesh cna <aneeshcna.gmail.com> wrote:
>
> > Hi Karl,
> >
> > Thanks for the reply. Since testing the fitness of each force-field terms
> > will be time consuming, I fee it could be better to check the role of
> > temperature on ligand conformation before getting into those QM-MM
> > calculations. Looking from this aspect, I have a quick query that what
> > could be the lowest possible temperature where I can do a classical MD
> > simulation?
> >
> >
> > Thanks in advance
> >
> >
> > Regards,
> > Aneesh
> >
> >
> > On Tue, Jan 29, 2013 at 9:29 PM, Karl N. Kirschner <
> > kkirsch.scai.fraunhofer.de> wrote:
> >
> > > Hi Aneesh,
> > >
> > > It is difficult to say if your simulations went wrong or not. For
> one,
> > > maybe your ligand is sampling conformations that are appropriate for a
> room
> > > temperature solution-phase model (assuming that is what you are
> doing). The
> > > crystal structure was likely solved at a much lower temperature,
> resulting
> > > in the preferred conformation you see in the PDB file.
> > >
> > > With that said, one could investigate how well the different
> force-field
> > > terms that you are using perform at reproducing known experimental
> > > observables in analogues, if available. Alternatively you could see how
> > > they reproduce QM-generated rotational curves for that molecule or a
> > > smaller analogue. Doing so may provide you some confidence in their
> use in
> > > MD simulations. (Be forewarned, this can be time consuming to
> accomplish.)
> > >
> > > Best regards,
> > > Karl
> > >
> > > ----- Original Message -----
> > > From: "aneesh cna" <aneeshcna.gmail.com>
> > > To: "AMBER Mailing List" <amber.ambermd.org>
> > > Sent: Tuesday, January 29, 2013 2:12:38 PM
> > > Subject: [AMBER] Fwd: Regarding the problem with ligand conformation
> > >
> > > Dear Amber users,
> > >
> > > I am working with the protein-ligand systems. The protein-ligand
> complex
> > > structure was obtained from Protein Data Bank. Before starting the
> > > simulation, I have carried out QM calculation ( b3lyp/6-311+g* ) of
> ligand
> > > to get the optimized structure and ESP fitted point charge for the
> atoms.
> > > The optimized ligand geometry was similar to the crystal structure.
> Then, I
> > > have used the antechamber module of Amber to prepare the parameter
> file (
> > > PREP and FRCMOD files) for the ligand, where I used the GAFF force
> field.
> > >
> > > Unfortunately, the ligand geometry has been changed drastically during
> the
> > > initial stages of production run ( after ~1ns of equilibration phase)
> of
> > > simulation. The ligand keep its proper conformation ( i.e. close to
> > > crystal conformation) for the initial ~1 ns phase of equilibration. Is
> it a
> > > problem with force field? . If so ( i.e., if there is any problem with
> > > ligand FF parameters), the observed conformational changes should
> happen in
> > > the initial stage of the simulation rather than at the end of ~1ns
> > > equilibration.
> > >
> > >
> > > Can anyone help me to figure out what went wrong with my simulation.
> > >
> > >
> > > I have attached three snapshot of the ligand (crystal structure, QM
> > > optimized, after equilibration respectively), for your reference.
> > >
> > >
> > >
> > > Thanks in advance
> > >
> > >
> > > Sincerely
> > > Aneesh
> > >
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Received on Tue Jan 29 2013 - 23:30:03 PST
