On 7/17/18 9:22 PM, Anderson, Amos wrote:
Hi Gromacs users,
I’ve never used gromacs before, so sorry if this question has an obvious answer
somewhere — it seems like the sort I should have been able to find an answer
for…
I want to write a python script to prepare an arbitrary pdb for use with gromacs
(e.g., does these steps http://www.mdtutorials.com/gmx/complex/01_pdb2gmx.html for
the user). The input pdb to my script may have waters, ions, and ligand(s) in it
already. In the tutorial it says "you are going to want to strip out the
crystal waters, PO4, and BME. Note that such a procedure is not universally
appropriate (i.e., the case of a bound active site water molecule).” The wording
maybe implies that other than active site waters and the ligand of interest, I’d
never want to preserve HETATOMs in my input file?
If not, and if I do want to keep them, how do I? Do I just treat all of them
like ligands in the tutorial, e.g., maybe a protocol like this (more precise
for ions I care about)?
* grep HETATOM my.pdb > hetatoms.pdb
HETATM, but yes.
* gmx editconf -f hetatoms.pdb -o hetatoms.gro
* copy/paste hetatoms.gro into my main .gro file (is there
python/utility anywhere for merging .gro files I could leverage?)
Conversion to .gro format is unnecessary; GROMACS handles PDB and other
formats, if you prefer.
* for ions gromacs doesn’t already know about (ions.itp), follow the
instructions described here:
http://www.mdtutorials.com/gmx/complex/02_topology.html
Parametrization servers won't generally deal with monoatomic species. In
a pairwise additive force field, the charge is already fixed and LJ have
to be tuned, typically based on free energy of solvation.
(in other words, I’m puzzled why pdb2gmx is complaining about ions it should
already know about from the built-in ions.itp)
pdb2gmx doesn't know anything about ions.itp, that comes in later when
calling grompp. pdb2gmx only knows about what is defined in the force
field .rtp file(s).
-Justin
--
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Justin A. Lemkul, Ph.D.
Assistant Professor
Virginia Tech Department of Biochemistry
303 Engel Hall
340 West Campus Dr.
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jalem...@vt.edu | (540) 231-3129
http://www.thelemkullab.com
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