Res ‘HIS’ is converted into ‘X’ after protonation – User discussions

GROMACS version:2022.2
GROMACS modification: Yes/No
@jalemkul
I am using CHARMM36-mar2019 for Protein-Protein MD simulation.
For the protonation of ‘HIS’ I am converting pdb into pqr using **pdb2pqr30** at pH=7.
Next I’m assigning charges manually using command pdb2gmx -f xyz.pdb -o xyz.gro -water tip3p -ignh -merge all -ff charmm36-mar2019 -his.
xyz.gro has HISD and HISE Residues which is obvious.

Problem:
Upon visualizing .gro or MD movie, it shows ‘X’ instead of ‘HIS’. Is it okay to go with the MD simulation? Does this impact the simulation?

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