[gmx-users] multiple chain restrain problem

[Albert]

Hello:

  I've got two protein chain in my system. I generate gmx.pdb by pb2gmx, 
and gromacs generate toplogy and restrain file for each chain:

gmx.pdb
  topol_chain_A.itp
topol_chain_B.itp
porschain_A.itp
porschain_B.itp

I noticed that the gmx.pdb doesn't contain any chain information. I am 
going to equilibrate the system first restrain the heavy atoms which can 
be specified by porschain_A.itp and porschain_B.itp. However, in the 
next step I am going to restrain only the backbone of chain A, how can 
we to do this? The chain information in new generated gmx.pdb lost.... 
When I use command:

genrestr -f gmx.pdb -p porsB

it doesn't contains selection for chain....

thank you very much

Albert