AMBER Archive (2009)

Subject: RE: [AMBER] database

From: FyD (
Date: Wed Sep 16 2009 - 13:56:16 CDT


> What I am trying to do is build one topology file and one inpcrd
> file containing both ligand (dCTP) and protein.

It is what I guessed ;-)

> I believe I then need to load leaprc.ff03 followed by dCTP2.mol2
> whose atom names have to match those in my protein/ligand PDB file
> (crystal structure)...right?


> The problem I ran into was that using the dCTP2.mol2 atom names
> which are not unique was not working.

Indeed, an atom name has to be unique in a _same_ residue, yes; but an
atom name can be repeated in different residues.

> That is, just calling all phosphates "P" in my protein/ligand PDB
> file (making it the same names as those of the dCTP2.mol2 file)
> fails to work.

P is indeed found three times in dCTP2 but it is "unique" since it is
found in three different residue numbers: i.e. in the numbers 1, 2 &
3. the fact that residues 2 & 3 have the same name does not matter
since they have a different residue number.

In fact, it is exactly the same case than the CA alpha atom in the
ALA-GLY-GLY peptidic sequence.

> So, I guess I need to rename atom names in dCTP2.mol2 and make them
> correspond to those *unique* atom names in my ligand(dCTP)/protein
> file..right?

No I do not think so. This is difficult to say without doing it.
But, I would say that you need to load in LEaP a protein/dCTP2 complex
(in the PDB file format). I would first try the following residue
ATOM protein whatever set of Cartesian coordinates
ATOM etc... ...
ATOM 1 OR P2M x whatever set of Cartesian coordinates
ATOM 2 P P2M x ...
ATOM 3 OP1 P2M x ...
ATOM 4 OP2 P2M x ...
ATOM 5 OP3 P2M x ...
ATOM 6 OR P1 y ...
ATOM 7 P P1 y ...
ATOM 8 OP1 P1 y ...
ATOM 9 OP2 P1 y ...
ATOM 10 OR P1 y ...
ATOM 11 P P1 y ...
ATOM 12 OP1 P1 y ...
ATOM 13 OP2 P1 y ...
ATOM 14 O3' C5 z ...
                  etc for residue 4 until the end of dCTP2

You need to try but I would say that the presence of the TER words
should match the residue number of the mol2 file...

Do not hesitate to ask for more questions her...

regards, Francois

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