Residues interacting with a specific ligand in a set of pdb structures

Question

[db42]

Dear all, I have a set of PDB structure. They all have a specific ligand. I want to know which residue in each structure interact with that ligand. For a single structure, I can use pdbsum ( for example here: http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetLigInt.pl?pdb=3au9&ligtype=01&ligno=01). Or I can also use Discovery Studio but for a single structure. What if I want to do it in batch? Thank you for your help