The Fab crystal structures can be obtained from Protein Data Bank (PDB). After downloading the PDB file, we need to clean the PDB file to remove water, ions, ligands, and other proteins. We can use PyMOL to select antibody heavy chain and light chain sequences and export their structures. Figure shows an example of the infliximab Fab structure (PDB code: 4G3Y) and how to use PyMOL to export the target structure. We can select the heavy and light chain residues using PyMOL and export the selected structure.