Splitting PDB File into Chains and Ligands Without using Tools
  Protein Data Bank (PDB) file format is a representation of a three-dimensional (3D) structure of the protein and ligand data extracted by interpreting the experimental result of high-energy electromagnetic radiation (X-ray) or Nuclear Magnetic Resonance (NMR) through the computational method. The standard PDB file format  was created by RCSB during the 1970s for parsing through software.  The atomic coordinate entries of protein are represented by ATOM  & TER  fields, and ligand by HETATM  field (given in the table below).     Record Type Columns Description  ATOM 1 - 4 "ATOM"  7 - 11 Atom serial number  13 - 16 Atom name  17 Alternate location indicator  18 - 20 Residue name  22 Chain identifier  23 - 26 Residue sequence number  27 Code for insertions of residues  31 - 38 X orthogonal Å coordinate  39 - 46 Y orthogonal Å coordinate  47 - 54 Z orthogonal Å coordinate  55 - 60 Occupancy  61 - 66 Temperature factor  73 - 76 Segment identifier  77 - 78 Element symbo...