def _build_atom_unique_id(atom_line):
    """Returns a unique identifying tuple from an ATOM line"""

    # unique_id: (name, altloc, resi, insert, chain, segid)
    unique_id = (atom_line[12:16],
                 atom_line[16],
                 int(atom_line[22:26]),
                 atom_line[26], atom_line[21],
                 atom_line[72:76].strip())

    return unique_id