Histidine (HIS) can be neutral or positively charged in this range. In this work, we used the CHARMM36m force fields. The titration states for HIS can be HSP (+1), HSD (+0), or HSE (+0). The default is HSP in the tcl script. We copy the Infliximab_mod.pdb to Infliximab_pqr.pdb and change the residue name of all histidine to HIS. Next, we used the pdb2pqr tool to determine the titration states by the following command.