[gmx-users] Regarding engineered residue topology

[Justin Lemkul]

On 7/27/15 1:21 AM, Venkat Reddy wrote:
> Dear Justin,
> Thank you for the prompt reply. I have checked the topology file once again
> and confirmed the dihedral (CB2-CA-CB1-HB11) thats creating problem. The
> Aib parameters are indeed available for OPLS-AA ff. But I couldn't locate
> the dihedral parameters for the above mentioned dihedral angle in
> ffbonded.itp file. However I found dihedral parameters for X-CA-CB-X. So,
> can I use X-CA-CB-X parameters for CB2-CA-CB1-HB11 dihedral?
>

You're confusing atom names and atom types.  The names are totally irrelevant 
for parameter assignment.  The CB2-C1-CB1-HB11 dihedral has a sequence of 
nonbonded types of opls_135-opls_225B-opls_135-opls_140, which have bonded types 
(see second column of ffnonbonded.itp) of CT-CT_2-CT-HC.  So the parameters you 
need are for CT-CT_2-CT-HC, which are indeed not in ffbonded.itp.

-Justin

> On Mon, Jul 27, 2015 at 5:46 AM, Justin Lemkul <jalemkul at vt.edu> wrote:
>
>>
>>
>> On 7/24/15 9:20 AM, Venkat Reddy wrote:
>>
>>> Dear all,
>>> I am trying to simulate a peptide with engineered residues like Aib (alpha
>>> amino-isobutyric acid). I am trying to use OPLS-aa forcefield. Though
>>> everything went well initially during topology generation, grompp showed
>>> the following error.
>>>
>>> ERROR 1 [file topol.top, line 2316]:
>>>     No default Ryckaert-Bell. types
>>> ERROR 2 [file topol.top, line 2317]:
>>>     No default Ryckaert-Bell. types
>>> ERROR 3 [file topol.top, line 2318]:
>>>     No default Ryckaert-Bell. types
>>> ERROR 4 [file topol.top, line 2325]:
>>>     No default Ryckaert-Bell. types
>>> ERROR 5 [file topol.top, line 2326]:
>>>     No default Ryckaert-Bell. types
>>> ERROR 6 [file topol.top, line 2327]:
>>>     No default Ryckaert-Bell. types
>>>
>>> The cross-check with topolo.top identified the dihedral CB2-CA-CB1-HB11 is
>>> throwing the error. My question is, even though the parameters for Aib are
>>> available in OPLS ff, why I am getting this error?
>>>
>>>
>> grompp doesn't lie.  Either you're looking at the wrong lines or you're
>> looking at the wrong parameters.  Some residues are constructed for
>> convenience but if they're not "official" then there may be problems.
>>
>> -Justin
>>
>> --
>> ==================================================
>>
>> Justin A. Lemkul, Ph.D.
>> Ruth L. Kirschstein NRSA Postdoctoral Fellow
>>
>> Department of Pharmaceutical Sciences
>> School of Pharmacy
>> Health Sciences Facility II, Room 629
>> University of Maryland, Baltimore
>> 20 Penn St.
>> Baltimore, MD 21201
>>
>> jalemkul at outerbanks.umaryland.edu | (410) 706-7441
>> http://mackerell.umaryland.edu/~jalemkul
>>
>> ==================================================
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>
>
>

-- 
==================================================

Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441
http://mackerell.umaryland.edu/~jalemkul

==================================================