Re: [AMBER] Error in ligand paramterisation in tleap

From: Dr. Anselm Horn via AMBER <amber.ambermd.org>
Date: Fri, 9 Aug 2024 13:43:18 +0200

Simran,

it is not clear what exactly you did, since you did not include the
actual input pdb file of the complex nor the ligand library you created.
Your error description "trying to edit the atom types used in amber but
it is failing" does not allow for specific pieces of advice.

Force field parameterization is an advanced topic; often problems arise
from some unfamiliarity with the methodological background. Maybe the
tutorials on the Amber website as well as the manual provide you with a
sound starting point.
And perhaps there are already force field parameters available for your
ligand? Or a chemically similar ligand has been parameterized, and you
could build on that knowledge?

>From a practical point of view:
tleap.out tells us that you defined a ligand via ligand.prepi and
created additional parameters in ligand.frcmod, presumably using the
parm14SB force field. However, your ligand definition in the prepi file
does not match the ligand definition in the pdb input file (different
unit name/different atom names?)
tleap_1.out tells us that you defined a ligand via ligand.prepi and
created additional parameters in ligand.frcmod, presumably using the
gaff force field. However, your ligand definition in the prepi file does
not match the ligand definition in the pdb input file (different atom
names); maybe you mixed up atom names and atom types.

-> Your ligand in the input pdb file must have the same residue name and
atom names as in the prepi file, where the ligand is defined. Otherwise
this part of the input cannot be assigned any force field parameters,
and thus the save command fails. All this in turn depends on the force
field you choose to describe the ligand, and thus on the atom types you
assign to the ligand atoms and the parameters you use for the molecular
description.

Good luck,

Anselm

Bioinformatik | NHR.FAU
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Germany



Am 09.08.2024 um 12:23 schrieb Simran Modi via AMBER:
> Greetings,
> I am trying to simulate the protein ligand complex. I am getting errors in building complex in tleap i.e. recognition of atom types. I have been manually trying to edit the atom types used in amber but it is failing. I am hereby attaching the complex along with he error files. Please let me know the solution.
>
> Regards,
> Simran Modi
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Received on Fri Aug 09 2024 - 05:00:02 PDT
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