Another possibility is to use a force field which has already been
developed for small molecules that makes it easier to parameterize.
One example is the Generalized Amber Force Field for small molecules,
which can be used with the AMBER protein force fields (which, I might
add, have been ported to GROMACS by the Pande group). I use these
together in GROMACS for ligand binding simulations (and free energy
calculations) and have been reasonable successful in some model
systems. You can get some preprints explaining how I do it from my web
site, if you want. http://www.dillgroup.ucsf.edu/~dmobley/
David
On 4/12/07, Mark Abraham <[EMAIL PROTECTED]> wrote:
pkmukher wrote:
> Dr Spoel,
>
> Thanks for your suggestions. Actually i would be using the
> GROMOS96 force field(option 0 in pdb2gmx GROMOS96 43a1).I am
> new to the GROMACS package.I wish to simulate a
> ligand-protein system and had been using the drug-enzyme
> tutorial available for this purpose. In the tutorial they
> use the PRODRG2 server to generate the ligand structure
> files. I find that the charges were calculated for a
> structure with only polar hydrogens present. This is then
> used to form the ligand-protein complex and solvation,
> neutralization etc.I was wondering
>
> 1) which ligand file should i use to generate my gaussian
> inputs. one with all the hydrogens or one with just the
> polar hydrogens.
Well the latter won't get you very far.
> 2) I presume that for the gaussian calculation I have to
> submit an all hydrogen structure. In that case how do I
> refit the charges onto the polar hydrogen only structure
> which i will use for the generataion of the ligand-protein
> complex(as per the tutorial)
Not a simple question. Force field extension is a dark art and very easy
to do badly. You can search the mailing list for advice people have
given before on this topic, but it's mostly been me and Tsjerk, and we
mostly tell people they are crazy to start their MD experience
parameterizing an extension for a force field. That doesn't seem to stem
the flow of (under)graduate students being set tasks that are likely to
be beyond their capacity to do without expert supervision - and if they
had that they wouldn't need to ask basic questions about parametrization
on a mailing list. Nonetheless, you must read up on how the rest of the
force field was developed in order to come up with an even vaguely
reasonable strategy for extending it.
> 3) Do you think that the current forcefield is good for
> simulation of ligand-protein complexes.
You should find some relevant literature and read it yourself :-)
Mark
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