Thanks so much for all the replies. I am sorry that in my last test run and post one hydrogen atom was overlooked by me. Following your instructions, now I can build the parameters of AdoMet with antechamber successfully. Since AdoMet contains a sulfonium group, I am wondering whether gaff can provide stable parameters for the system now? If not, I am going to combine the parameters for sulfonium group in the supporting material of BioChem 2002,41,7636 with the param99.dat to build a full model used in MD simulation. But I still have some questions in the process of the work and need your great help.
1. Is it a reasonable way by using the parm99.dat instead of the gaff.dat to build a new unit in AMBER? Or should I just use the parameters for sulfonium group in the mentioned paper and the parameters in gaff.dat for the rest of the system? The reason why I want to use parm99.dat is that AdoMet is an combination of MET and part of ADE ( the adenine and the ribose) for which parm99.dat can provide more specific parameters.
2. If the answer in 1 is yes, then the following steps are adopted to finish the job. Firstly, the antechamber was used with the sam.pdb file as the input to get a prep file, sam.prepin. Then the atom types in sam.prepin file were substituted by atom types in parm99.dat and keep the charges calculated by antechamber in the first step unchanged. Finally, the missing parameters relating to the sulfonium group were prepared in a file called sam.frcmod. Is it ok to do so?
3. It seems that the energy expression of torsional interactions in the paper is different with the one used in AMBER10.
Et = V1/2*(1+Cos(phi))+V2/2*(1+Cos(2*phi))+V3/2*(1+Cos(3*phi)) in the paper.
For example, the parameters for SP-CT-CT-CT interaction in the paper is as follows:
----------------
Torsional Interaction (Kcal/mol)
V1/2 V2/2 V3/2
SP ¨C CT ¨C CT ¨C CT -1.6814 1.0698 -0.0001
----------------
Then how to convert the parameters in the paper to the ones used in AMBER10, Vn/2-potential barrier, gamma-phase offset, n-periodicity of the torsion and the number of bond paths?
4. It seems that antechamber produces different charge values for different configurations of AdoMet. Which one should I use?
5. Is there a detailed document for the format and explanation of the amber FF? I am not very clear how to calculate the number of the bond paths in torsion interaction.
Any suggestion is greatly appreciated and thanks so much for your time.
Have a nice day.
-------
Jeffrey
>On Tue, Nov 25, 2008, Jeffrey wrote:
>>
>> Thanks so much for your instruction, David.
>>
>> When running antechamber with all hydrogens, something strage was observed
>> in the output. As in AdoMet, the sulfur atom is a sulfonium resulting in a
>> system with 1 net positive charge. But the output message showed that the
>> net charge was zero...
>
>
>> [c0225 sam]$ antechamber -i sam.pdb -fi pdb -o sam.prepin -fo prepi -c bcc -s 2
>
>If you have a net charge, you need to use the "-nc" flag in antechamber.
>
>> Total number of electrons: 210; net charge: 0
>
>However, since you have 210 electrons in a neutral system, you would have 209
>electrons with a +1 charge. But antechamber can only handle closed shell
>systems with an even number of electrons.
>
>Your SAM structure appears to be missing a proton at the O3' position.
>
>...dac
>
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Received on Fri Dec 05 2008 - 16:43:43 PST
