Hi I am doing a peptide simuation that have CYS but by default pdb2gmx put my CYS as CYSH and i need that CYS deprotonated(and without s-s) i read the rtp files and found CYS1 CYS2 How can i use this residues. i probe change the pdb file (CYS --->CYS1) but pdb2gmx says CYSH :-( What can i do? Thanks Osmany