As large structures (containing >62 chains and/or 99999 ATOM lines) cannot be represented in the legacy PDB file format, data are available in the PDB archive as single PDBx/mmCIF files representing the entire structure, 
and as TAR files containing a collection of best effort/minimal files in the PDB file format to support users and software tools that rely solely on the PDB file format. 

In each TAR file, an entire structure is divided into several minimal files. TAR files are available in a separate directory in the PDB FTP archive (ftp://ftp.wwpdb.org/pub/pdb/compatible/pdb_bundle/) 
grouped by the middle two characters of the 4-character PDB ID.

Each TAR file contains the following-

1. Best effort/minimal PDB format files that contain only authorship, citation details and coordinate data under HEADER, AUTHOR, JRNL, CRYST1, SCALEn, ATOM, HETATM records.
The following PDB records are not included in the best effort/minimal files: 
OBSLTE, TITLE, CAVEAT, COMPND, SOURCE, KEYWDS, EXPDTA, REVDAT, SPRSDE, REMARKS, DBREF, SEQADV, SEQRES, MODRES, HET, HETNAM, HETSYN, FORMUL, HELIX, SHEET, SSBOND, LINK, CISPEP, SITE, ORIGXn, MTRIXn, CONECT.

2. An index file with the mapping between the chains present in the large entry and the chains present in the minimal PDB format files.


Example: Truncated best effort/minimal file for the entry 4u50

HEADER    RIBOSOME                                2014-07-24  XXXX
AUTHOR    N.GARREAU DE LOUBRESSE, I.PROKHOROVA, G.YUSUPOVA, M.YUSUPOV
JRNL        AUTH   N.Garreau de Loubresse, I.Prokhorova, W.Holtkamp,
JRNL        AUTH 2 M.V.Rodnina, G.Yusupova, M.Yusupov
JRNL        TITL   Structural basis for the inhibition of the eukaryotic
JRNL        TITL 2 ribosome.
JRNL        REF    Nature                        V. 513   517 2014
JRNL        REFN        NATUAS  UK      1476-4687
JRNL        PMID   25209664
JRNL        DOI    10.1038/nature13737
CRYST1  434.390  285.580  303.060  90.00  98.99  90.00 P 1 21 1      4
SCALE1      0.002302  0.000000  0.000364        0.00000
SCALE2      0.000000  0.003502  0.000000        0.00000
SCALE3      0.000000  0.000000  0.003341        0.00000
ATOM      1  P     U A   1     -88.608  31.952  64.746  1.00 81.64           P
ANISOU    1  P     U A   1     5964  13260  11795   1046   -383  -1793       P
ATOM      2  OP1   U A   1     -88.681  32.341  63.314  1.00 82.66           O
ANISOU    2  OP1   U A   1     6111  13412  11886   1075   -507  -1778       O


Example: Truncated index file for the entry 4u50

New chain ID            Original chain ID

4u50-pdb-bundle1.pdb:
           A                         2
           B                        S0
           C                        S1
           D                        S2
...

An index of all large structure entries (that do not have a standard PDB format file) is updated regularly on the PDB FTP site at ftp://ftp.wwpdb.org/pub/pdb/compatible/pdb_bundle/pdb_bundle_index.txt. 
This list will continue to grow as new large structures are deposited and released.