I'm learning to use the GOLD software for molecular docking, and was trying to dock colchicine at the 1SA0 binding site. One of the most important interactions is the hydrogen bond between CYS241 and one of the oxygens of a methoxy group of the ligand.

So I was trying to set up the HBond constraint on the hydrogen atom ("HG" I do not know what atom type is that) of thiol group so that could be a donator, but there's nothing I can do to make it work. Here is the error message:

Fatal error:

Illegal mapping constraint: protein hydrogen HG (id 11645) is not donable, or not accessible to the ligand

I know that this Hbond exists, because it is described in the PDB page, and in this review .

For the preparation of the protein, first I downloaded the PDB, removed all the chains except for "A" and "B", added the missing side chains with WATH IF web server, then, because I was learning molecular dynamics in GROMACS, I decided run an MD to minimize the protein and correct the position of the added atoms. I do not know if this gets in the way, because of the attribution of atom types (type not recognized by GOLD), or somethig else.