A series of PDB related databases for everyday needs.
Wouter G Touw, Coos Baakman, Jon Black, Tim AH te Beek, E Krieger, Robbie P Joosten, Gert Vriend.
Nucleic Acids Research 2015 January; 43(Database issue): D364-D368.

Dictionary of protein secondary structure: pattern recognition of hydrogen-bonded and geometrical features.
Kabsch W, Sander C,
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PMID: 6667333; UI: 84128824. 
