From: zeynab mohamad hoseyni (zmhoseyni_at_yahoo.com)
Date: Tue Feb 18 2014 - 14:30:00 CST
I used the mentioned server to predict the protonation states of Histidine mainly. The server does it according to the Pka values calculated using the ProPka server.
Histidine is one of the polar amino acids who are called titratable amino acids (http://enzyme.ucd.ie/main/index.php/Introduction_to_pKa_calculations).
Note that in the CHARMM topology file the charges assigned to the atoms of each residues are fixed and for example all ARG residues are composed of atoms
with fixed charges and doesn't matter where they are located while in reality the Pka values for the ARG residues placing on the surface of protein (facing waters)
are different from those located in the interior of the protein (http://en.wikipedia.org/wiki/Protein_pKa_calculations). This means that the charge distribution has to
be different for those ARG residues experiencing different environment. PQR contain the charge distribution for the atoms of residues according to the Pka calculation. So I was trying to use those partiol charges in my psf file..
The HIS case is much more delicate as its Pka is closed to the PH of water. So any small changes in the PH could change the protonation state of HIS to be one of HSE,
HSD or HSP. These are all I know...
All the Best,
On Tuesday, February 18, 2014 4:10 PM, MEHRAN MB <mb.mehran1_at_gmail.com> wrote:
On Sun, Feb 16, 2014 at 10:54 AM, zeynab mohamad hoseyni <zmhoseyni_at_yahoo.com> wrote:
>I use pdb2pqr (http://nbcr-222.ucsd.edu/pdb2pqr_1.8/) server to add hydrogen atoms to the protein structure.
I have no experience in pdb2pqr, but it seems it is not designed to add hydrogen atoms
"This server enables a user to convert PDB files into PQR files. PQR files are PDB files where the occupancy and B-factor columns have been replaced by per-atom charge and radius."
The server produces pqr file containing protein coordinates (including the hydrogen atoms) as well as the charges assigned to each atom.
>These charges are different from those provided by topology file
if you could make psf file (probably using AutoPSF plugin) it should gave you pdb file including hydrogen atoms too. So I am not sure why you are using PQR?1?!
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