Hi Tommaso,
I have encountered a similar problem recently, I don't think it involves the glycam06g force field directly, but something with how xleap (didn't try tleap) interprets the force field when sourcing the protein/dna force field. If you look at the output structure of leap, I think you will see that a few of the hydrogen atoms are incorrectly placed. I corrected this by only loading glycam06 parameters and suppressing the the protein force field loading (i.e. xleap -s -f leap.in). This then gave me the correct spatial structure of the carbohydrate. (I have not tried to reproduce this error using gleap or sleap.) However, if this works for you, then I think you will need to include the ions into glycam sourcing (I am pretty sure their parameters are sourced with the protein force field only, but not 100% sure about that).
Cheers,
Karl
----- Original Message -----
From: "tommaso casalini" <tommaso.casalini.mail.polimi.it>
To: amber.ambermd.org
Sent: Friday, February 17, 2012 8:35:00 PM
Subject: [AMBER] Issues with hydrogens using glycam force field in Amber 10
Dear Amber developers and users,
I have a problem with hydrogens, using GLYCAM_06 force field with Amber 10.
Glycam parameters version is Glycam_06g.dat.
I built hyaluronic acid dodecamer thanks to tleap, since I have to
investigate BMP2/HA interactions.
However, performing MD simulations and studying trajectories, I found
these problems:
1) C-H bond stretches a lot even if I apply SHAKE;
2) hydrogen atoms of methyl and hydroxyl groups rotate, it seems that
dihedral force constant is null or something like that.
There are some details:
I built hyaluronic acid with tleap, loading GLYCAM_06 parameters.
The HA chain is a sequence of 3YB and 4ZP units, saturated with OME groups.
I did not load any .frcmod file in order to modify ff parameters.
I performed simulations both in implicit and explicit solvent, but I
can see these issues in both cases.
It is very important for me that hydrogens are described properly,
since hydrogen bonding is an important interaction in the system I am
investigating.
I thank in advance for your help!
Tommaso Casalini, Ph.D Fellow
CFA lab, Politecnico di Milano
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Received on Fri Feb 17 2012 - 17:30:01 PST
