Appendix 7: Order of Records

(This information is repeated from the Introduction.)

All records in a PDB coordinate entry must appear in a defined order. Mandatory record types are present in all entries. When mandatory data are not provided, the record name must appear in the entry with a NULL indicator. Optional items become mandatory when certain conditions exist. Record order and existence are described in the following table:

RECORD TYPE                 EXISTENCE      CONDITIONS IF OPTIONAL                
---------------------------------------------------------------------------------
HEADER                      Mandatory                                            

OBSLTE                      Optional       Mandatory in withdrawn entries.       

TITLE                       Mandatory                                            

CAVEAT                      Optional       Mandatory if structure is deemed      
                                           incorrect by an outside editorial   
                                           board.                               

COMPND                      Mandatory                                            

SOURCE                      Mandatory                                            

KEYWDS                      Mandatory                                            

EXPDTA                      Mandatory                                            

AUTHOR                      Mandatory                                            

REVDAT                      Mandatory                                            

SPRSDE                      Optional       Mandatory if a replacement entry.     

JRNL                        Optional       Mandatory if a publication describes  
                                           the experiment.                     

REMARK 1                    Optional                                             

REMARK 2                    Mandatory                                            

REMARK 3                    Mandatory                                            

REMARK N                    Optional                                           

DBREF                       Optional       Mandatory for each peptide chain with 
                                           a length greater than ten (10)      
                                           residues, and for nucleic acid.      
                                           entries that exist in the Nucleic   
                                           Acid Database (NDB).                 

SEQADV                      Optional       Mandatory if sequence conflict exists.

SEQRES                      Optional       Mandatory if ATOM records exist.      

MODRES                      Optional       Mandatory if modified group exists    
                                           within the coordinates.              

HET                         Optional       Mandatory if non-standard group other 
                                           than water appears in the entry.     

HETNAM                      Optional       Mandatory if non-standard group other 
                                           than water appears in the entry.      

HETSYN                      Optional                                     

FORMUL                      Optional       Mandatory if non-standard group or    
                                           water appears.                       

HELIX                       Optional                      

SHEET                       Optional                       

TURN                        Optional                         

SSBOND                      Optional       Mandatory if disulfide bond is present.

LINK                        Optional                                             

HYDBND                      Optional                                             

SLTBRG                      Optional                                             

CISPEP                      Optional                                             

SITE                        Optional                                             

CRYST1                      Mandatory                                             

ORIGX1 ORIGX2 ORIGX3        Mandatory                                             

SCALE1 SCALE2 SCALE3        Mandatory                                             

MTRIX1 MTRIX2 MTRIX3        Optional       Mandatory if the complete asymmetric   
                                           unit must be generated from the given
                                           coordinates using                    
                                           non-crystallographic symmetry.        

TVECT                       Optional                        

MODEL                       Optional       Mandatory if more than one model    
                                           is present in the entry.              

ATOM                        Optional       Mandatory if standard residues exist.  

SIGATM                      Optional                                              

ANISOU                      Optional                                              

SIGUIJ                      Optional                                              

TER                         Optional       Mandatory if ATOM records exist.       

HETATM                      Optional       Mandatory if non-standard group 
                                           appears.

ENDMDL                      Optional       Mandatory if MODEL appears.            

CONECT                      Optional       Mandatory if non-standard group        
                                           appears.                              

MASTER                      Mandatory                                             

END                         Mandatory                                             

Note that a PDB file existing outside of the PDB official release may contain locally-defined records beginning with "USER". The PDB reserves the right to add new record types (not beginning with "USER"), so programs which read PDB entries should be prepared to read (and ignore) other record types. PDB will follow standard procedures whenever format changes are proposed.

Sections of an Entry

The following table lists the various sections of a PDB coordinate entry and the records comprising them:

SECTION              DESCRIPTION                    RECORD TYPE                   
----------------------------------------------------------------------------------
Title                Summary descriptive remarks    HEADER, OBSLTE, TITLE,        
                                                    CAVEAT, COMPND, SOURCE,       
                                                    KEYWDS, EXPDTA, AUTHOR,       
                                                    REVDAT, SPRSDE, JRNL          

Remark               Bibliography, refinement,      REMARKs 1, 2, 3 and others    
                     annotations                                           

Primary structure    Peptide and/or nucleotide      MODRES, DBREF, SEQADV, SEQRES 
                     sequence and the                                           
                     relationship between the                                
                     PDB sequence and that                                  
                     found in the sequence                                   
                     database(s)                                             

Heterogen            Description of non-standard    HET, HETNAM, HETSYN, FORMUL   
                     groups                                                     

Secondary structure  Description of secondary       HELIX, SHEET, TURN            
                     structure                                                  

Connectivity         Chemical connectivity          SSBOND, LINK, HYDBND,         
annotation                                          SLTBRG, CISPEP                

Miscellaneous        Features within the            SITE                   
features             macromolecule                                              

Crystallographic     Description of the             CRYST1                        
                     crystallographic cell                                      

Coordinate           Coordinate transformation      ORIGXn, SCALEn, MTRIXn, TVECT 
transformation       operators                                                  

Coordinate           Atomic coordinate data         MODEL, ATOM, SIGATM, ANISOU,  
                                                    SIGUIJ, TER, HETATM, ENDMDL   

Connectivity         Chemical connectivity          CONECT

Bookkeeping          Summary information,           MASTER, END                   
                     end-of-file marker