1. To retrieve a list of all available PDB entries, use the URL /oca-bin/ocaids?id=ALL.
2. To link to the Atlas page, use /oca-bin/ocashort?id=1ACE. It will retrieve the newest available ID.
3. To retrieve an obsolete entry, add the parameter obs=1 to send-pdb, as in this URL /oca-bin/send-pdb?obs=1&id=1ACE
4. To retrieve a gzip compressed PDB file, use /oca-bin/send-x-pdb?id=4HHB
5. Query OCA and get a list of PDB ids entries related to sclerosis with Zn as Associated group, use /oca-bin/ocaids?di=SCLEROSIS&ht=ZN (see at the bottom the list of valid query tags)

OCA query tags:

ht: Associated group
fa: Query sequence in FASTA format
au: Author, Family name of depositor or author of associated publication 
kw: Keyword, Molecule name, class or family, or related term
tx: Text, Any word in the complete PDB text 
ex: Method of Structure Determination
    values xrd  X-Ray Diffraction
           nmr  NMR
           sxr  Synchrotron X-Ray Diffraction
           edi  Electron Diffraction
           emi  Electron Microscopy
           fdi  Fiber Diffraction
           ndi  Neutron Diffraction
           ftr  Fluorescence Transfer
           mod  Theoretical Model
gn: Gene designation
fu: Function
di: Disease           

OCA valid data modes:
tag m
  ci PDB in mmCIF format
  xm PDB in XML(CML) format
  cc Crystal Cards
  sh PDB Header Only
  fu PDB w/Coordinates
  fa Sequences (FASTA format)
  su Summary