Florian,
I had the same problem and I couldnt get everything to work internally
in pymol. I never got pymol to write the *.pqr files. I couldn't
figure it out. However, you can give your pdb to the PDB2PQR server:
http://agave.wustl.edu/pdb2pqr/server.html
Strip the waters/ligands and load in your pdb. Choose that you want to
create an APBS input file. You get 2 files: *.pqr and *.in.  Rename
without .txt extension (if the output has them. My mac put them on).
You can load input pdb (the one with waters/ligands stripped).  Change
the temp file locations (temp.pqr, *.pdb, and APBS input file). Don't
change the "pymol generated dx".  Under main, choose "use another
pqr".  Choose "externally generated" pqr and browse for your x.pqr.
Click "set grid". Click "run APBS".  That will spit out a
"pymol-generated.dx". In pymol type load_dx [file].dx. In APBS window,
go to the visualization tab and choose "show mol. surface".  Change
levels and update.
Perhaps not the best way to get this to work, but it will give you a
surface to look at. Good luck,
Eric



On 11/22/06, Florian Schmitzberger <florian.schmitzber...@ki.se> wrote:
Dear All,

I am having a small problem using the apbs plugin in pymol on my pdb (I am
using fink installed pymol and apbs versions on Mac OSX 10.4.8).

When I try to run apbs I received the following message:

"Unable to assign parameters for 100 atoms in the selection unassigned.
Please either remove these unassigned atoms and re-start ..."

In principle, I think I understand the problem is that pdb2pqr cannot assign
charges to certain atoms, in my case posttranslationally modified cysteine
residues.

My question would be what the best way to fare with those atoms is. Since
the modification introduces an acidic patch, if possible I would like to
leave the atoms in (rather than remove them) when calculating surface charge
representation, as this could be informative.

So perhaps my question boils down to what the optimal way to manually assign
reasonable charges (in the pqr-file) for this oxidised cysteine (sulfinic
acid; O-S=O) is.

I also noticed that I get the same error message with residues where
side-chain atoms have been removed (such as surface lysines), while leaving
the original residue name. But then I suppose there is no way around this.

Thank you very much in advance for any comments!

Best regards,

Florian

--------------------------------------------
Florian Schmitzberger
Medical Biochemistry and Biophysics
Karolinska Institute
Scheeles vaeg 2
SE-171 77 Stockholm, Sweden
Tel: +46-8-524-86875




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