Sajad Ahrari wrote:
tnx for your help Justin!
but shouldn't the topology of S atom be described for gromacs? unless gromacs may know P atom with the same topology as S. although they may not be the same!?

You're talking about two separate issues - atom types and parameters for molecules. Yes, most (all?) force fields describe both P and S atoms, but I guarantee none of them have (by default) parameters for some species named "d" that represents ADP-SO4. You cannot assign parameters from P blindly to S and hope for the best. That sounds fundamentally wrong to me.

In your original message, it sounded like you wanted to change ADP-SO4 into ATP, but perhaps I misunderstood what you intended. No force field will be able to assign parameters to ADP-SO4, even though the force field may recognize individual atoms, it cannot construct a topology for any arbitrary molecules.

If you need to simulation this ADP-SO4 species, you're in for the long road of parameterization:

http://www.gromacs.org/Documentation/How-tos/Parameterization

Otherwise, change the S atom to P and name the molecule ATP so it will be recognized by whatever force field you choose, after you have verified that the force field can indeed recognize such a species. Otherwise, you're stuck doing parameterization for ATP, too.

-Justin

regards
sajad

------------------------------------------------------------------------
*From:* Justin A. Lemkul <[email protected]>
*To:* Discussion list for GROMACS users <[email protected]>
*Sent:* Sat, April 23, 2011 5:54:58 AM
*Subject:* Re: [gmx-users] dealing with ATP



Sajad Ahrari wrote:
 > Dear users
> i am working with a protein witch holds a hetero-atom in it's pdb structure. the hetero-atom is named "d" and stands for "ADP+SO4" (in fact the third phosphate of ATP is being substituted with SO4). i wanted to know if gromacs holds a feature to change "d" into ATP? and if so do

No, but you can use a text editor to replace the S atom with P.

 > i need to introduce ATP for Gromacs or it is known for the program?

Some force fields support ATP, some do not. Check the .rtp files and see what you find.

-Justin

 > i do appreciate your help!
 > sajad
 >

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

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu <http://vt.edu/> | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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