Cath Domain PDB (or DomPDB) files are text files that contain just the PDB ATOM records that correspond to the residues of a particular CATH domain. These are useful as they can provide the input for protein structure viewers to examine individual CATH domains, or by structure comparison algorithms to compare domains.

http://data.cathdb.info/v3_2_0/dompdb/1cukA01

ATOM      1  N   MET     1      -7.750  -4.498 -20.265  1.00 21.82
ATOM      2  CA  MET     1      -7.178  -5.177 -19.122  1.00 18.39
ATOM      3  C   MET     1      -7.857  -4.686 -17.798  1.00 20.00
ATOM      4  O   MET     1      -8.202  -5.472 -16.932  1.00 18.10
...